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 Prepress No. 1 and 2

Prepress No. 1 and 2

Symbol Description
1 Suction Strainer
This strainer is located beneath the fluid level. The strainer will filter
the large particles of contamination to the pump. If the strainer were
to become contaminated then the pump would cavitate. The pump
will have a high pitched whining sound when cavitating. Some
strainers have a built-in 2 or 3 PSI check valve. If this is the case, the
pump will not develop the high pitched whining sound. When the
vacuum pressure in the suction line reaches the rating of the check
valve spring, dirty oil will be directed to the pump. The strainer should
be removed from the reservoir on a regular basis and cleaned. The
strainer can be cleaned by blowing air from the inside out.

2 Pump
This 20 GPM, variable displacement, externally drained, pressure
compensating piston pump supplies a volume of oil to the prepress.
The pump will deliver maximum flow whenever pressure in the
system is below the setting of the compensator. When the pressure
reaches the compensator setting, the pump will de-stroke to deliver
only the amount of oil necessary to maintain the compensator setting
in the line. The compensator
pressure setting for this pump was
not specified. Please refer to our
Maintenance Basic Hydraulic
Troubleshooting manual, Hydraulic
Pumps section, for the procedure
for setting the pump compensator. If
the compensator is set too low, the
compression pressure will be low. A
setting that is too high will result in
shock and perhaps damage to the
machine.
2 Pump

Troubleshooting Press Hydraulics Page 1

Prepress No. 1 and 2

The compensator valve can fail either open or closed. If the valve fails
open, the pump will be de-stroked to a near 0 GPM flow rate and the
pressure at the outlet port will be very low. If the valve fails closed, the
pump will never de-stroke and will deliver maximum flow at all times.
Whenever the full pump volume is not being used in the machine,
pressure will build to the No. 2A relief valve setting and return to tank
at high pressure generating heat. If either problem exists, turn the
pump off and make sure the pressure at the outlet port is 0 PSI.
Remove the compensator from the pump and take it apart. Inspect
the hollow orifices in the valve spool for contamination. Make sure
that there is no trash inside the compensator housing. Verify that the
spring is not bent, broken or rusted. Re-assemble the compensator
and attempt to reset the spring to the proper setting.

Oil that bypasses internally across the tight tolerances in the pump
will drain back to tank through the case drain to keep pressure from
building against the shaft seal. As the pump wears, these tolerances
become greater, resulting in higher case flow. Thus case flow will
increase as the pump becomes more worn. The most effective way
to track pump wear is by measuring the amount of case flow. When
the pump is relatively new, case flow should be approximately 1 – 3%
of the total output, or about .2 – .6 GPM. If case flow increases to as
much as 10% of the total pump volume, the pump should be
replaced. The case drain line can be removed and ported into a 5
gallon bucket to check the flow rate. A flow meter can be installed in
the case drain line for convenient regular measurement of case flow.

2A Relief Valve
This valve is used as an extreme safety device in the system. In the
event the pump compensator was to fail closed, the valve would open
dumping any excess volume through the valve spool and back to the
tank. The tank line of this valve will be hot if this were to occur. It is
important that this valve be set above the setting of the compensator.
The recommended setting of this relief valve is 250-300 PSI above
the setting of the compensator. Please refer to our Maintenance
Basic Hydraulic Troubleshooting manual, Hydraulic Pumps section

Page 2 Troubleshooting Press Hydraulics

 Prepress No. 1 and 2

for properly setting the relief valve and pump compensator. If the
relief valve is set below the compensator, then the pump will deliver
maximum volume at all times. This means that any oil that the pump
is delivering that the system does not require will return to tank
through the relief valve spool. Heat will once again be generated
when this occurs. If this valve were to fail in the open position, then
the circuit would operate very slowly or not at all.

2A Relief Valve

2B Check Valve
The purpose of this check valve is to provide a backpressure of
approximately 65 PSI, which is necessary for shifting the No. 6 main
spool once either of the pilot valve solenoids is energized. If this
check were to fail open because of trash or a broken spring, then
adequate pressure would not build to shift the No. 6 valve.

Troubleshooting Press Hydraulics Page 3

Prepress No. 1 and 2

3 Return Filter
The oil that exhausts out of the No. 6 directional valve’s tank line is
ported through this filter before returning back to the tank. The
element’s condition should be checked regularly if provided with a
visual indicator. The element should also be set up to be changed on
a regular basis. This schedule can be established by an oil analysis
program. If the element plugs up and the inlet pressure reaches the
internal check valve’s setting (25 PSI), dirty oil will bypass the
element.

3 Return Filter

3A Heat Exchanger
The oil that exhausts out of the No. 6 directional valve’s tank line is
ported through tubes inside the shell of this heat exchanger before
returning to tank. The water flow is ported through tubes in the
opposite direction. The heat in the oil is transferred from the oil to the
water. To achieve the most efficient heat transfer, the water flow
should be 25% of the oil flow. The water flow can be controlled by
manual valves, a water modulating valve or an electrical solenoid
valve.

Page 4 Troubleshooting Press Hydraulics

 Prepress No. 1 and 2

Circulating hot wash oil or light distillate through the tube side or shell
side will usually effectively remove sludge or similar soft deposits.
Soft salt deposits may be washed out by circulating hot fresh water.
Some cleaning compounds such as “Oakite” or Dowell” may be
effective in removing more stubborn deposits.

3A Heat Exchanger

6 Directional Valve
To close the prepress, a voltage is applied to the “A” coil on the pilot
valve. Pilot pressure is directed internally into one side of the main
spool. The main spool then shifts into the “straight arrows” position.
Flow from the pump flows through the “P” and “A” ports then into the
full piston side of the jack ram. The oil in the rod side is forced out and
returns to the tank through the No. 8 flow control valve and the “B”
and “T” ports of this valve. The valve is maintained in the “A” position
in the “close prefills”, “pressurize main rams” and “compression”
cycles. Both solenoids are de-energized in the “decompression”
cycle.

Troubleshooting Press Hydraulics Page 5

Prepress No. 1 and 2

To open the prepress, a voltage is applied to the “B” coil on the pilot
valve. Pilot pressure is directed internally into one side of the main
spool. The main spool then shifts into the “crossed arrows” position.
Flow from the pump flows through the “P” and “B” ports then into the
rod side of the jack ram. The oil in the full piston side is forced out and
returns to the tank through the “A” and “T” ports.

This valve is a tandem center, three position, four way, double

solenoid, externally piloted, internally drained, spring centered
directional control. When replacing the valve, make sure the part
numbers match exactly as one letter or one number may mean that
the new valve has a different piloting and draining arrangement or a
different spool.

6 Directional Valve

Page 6 Troubleshooting Press Hydraulics

 Prepress No. 1 and 2

7 Directional Valve
This valve is mechanically actuated by the platen if a short stack or no
stack is in the prepress. The valve shifts open when actuated,
allowing the pump flow to vent back to the tank. Pressure will not
build up when this occurs. This is a normally closed, two position, two
way, mechanically actuated, spring return directional valve.

7 Directional Valve

8 Flow Control
This valve controls the speed at which the prepress closes. Care
should be taken not to close the valve too much, as this will create a
backpressure at the inlet of the jack ram. If the No. 10 check valve
setting (100 PSI) is reached before the platen contacts the stack of
veneer, the check valve will open, directing pilot pressure to close the
No. 13 prefill valves. Pressure will then continue building until the No.
9 sequence valve setting is reached. The pump flow will then begin
filling the main rams too soon. A very slow compression would be the
result. When opening the prepress, the oil will flow through the
internal bypass check valve.

Troubleshooting Press Hydraulics Page 7

Prepress No. 1 and 2

9 Sequence Valve
This valve must be set above the pressure required to close the
prepress. When the setting of the sequence valve is reached, the
pump flow is directed through the valve to pressurize the main rams.
If the valve sticks open, the pump volume will flow into the rams and
return to tank through the No. 13 prefill valves.

9 Sequence Valve & 12 Pilot Operated Check Valve

10 Check Valve
Once the platen
contacts the veneer,
pressure will build to
the setting of the
spring, 100 PSI. The
valve then opens,
directing pressurized
fluid to shift the prefill
valves closed.

10 Check Valve

Page 8 Troubleshooting Press Hydraulics

 Prepress No. 1 and 2

11 Check Valve
The No. 6 directional valve will de-energize when the compression
timer elapses. Pressurized fluid in the main rams will then bleed
through this check valve and back to tank through the “P” and “T”
ports of the directional valve main spool.

12 Pilot Operated Check Valve

When the No. 6 directional valve is energized in the “B” position to
open the prepress, pilot pressure is also directed to shift this check
valve open. Pressurized pilot fluid to the No. 13 prefill valves is ported
back to tank through this pilot operated check valve. The prefill valves
will then shift open connecting the oil in the main rams back to the
reservoir. If this check valve sticks open, the pilot pressure will not
build to close the prefill valves. The prepress will not go into the
compression mode if this occurs.

13 Prefill Valves
When closing the prepress, the prefill
valves are open allowing oil flow from
the reservoir to the main rams. When
the platen contacts the stack, the
pressure will build first to the No. 10
check valve setting, then to the No. 9
sequence valve setting. The No. 10
valve will then open, directing pilot
pressure to close the prefill valves.
When the No. 6 directional valve 13 Prefill Valve
energizes in the “B” position to open the
prepress, the No. 12 pilot operated check valve shifts open. Pilot
pressure in the prefill valve pilot lines is bled to tank through the No.
12 check valve. The prefill valves again shift open, hydraulically
connecting the main rams to the reservoir. As the prepress opens, oil
in the main rams returns to tank through the prefill valves. If a prefill
valve fails, pressure in the rams may build slowly or not at all.

Troubleshooting Press Hydraulics Page 9

Prepress No. 1 and 2

14 Pressure Switch
This switch is used to send a signal to start the compression timer.

Check Valves

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 Prepress No. 1 and 2

Troubleshooting Press Hydraulics Page 11

Prepress No. 1 and 2

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 Prepress No. 1 and 2

Troubleshooting Press Hydraulics Page 13

Prepress No. 1 and 2

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 Prepress No. 1 and 2

Troubleshooting Press Hydraulics Page 15

Prepress No. 1 and 2

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 Prepress No. 1 and 2

Troubleshooting Press Hydraulics Page 17

Prepress No. 3

Prepress No. 3
Symbol Description
1 Suction Strainer
This strainer is located beneath the fluid level. The strainer will filter
the large particles of contamination to the pump. If the strainer were
to become contaminated then the pump would cavitate. The pump
will have a high pitched whining sound when cavitating. Some
strainers have a built-in 2 or 3 PSI check valve. If this is the case, the
pump will not develop the high pitched whining sound. When the
vacuum pressure in the suction line reaches the rating of the check
valve spring, dirty oil will be directed to the pump. The strainer should
be removed from the reservoir on a regular basis and cleaned. The
strainer can be cleaned by blowing air from the inside out.

2 Pump
This 20 GPM, variable displacement, externally drained, pressure
compensating piston pump supplies a volume of oil to the prepress.
The pump will deliver maximum flow whenever pressure in the
system is below the setting of the compensator. When the pressure
reaches the compensator setting, the pump will de-stroke to deliver
only the amount of oil necessary to maintain the compensator setting
in the line. The compensator pressure setting for this pump was not
specified. Please refer to our Maintenance Basic Hydraulic
Troubleshooting manual, Hydraulic Pumps section, for the
procedure for setting the pump compensator. If the compensator is
set too low, the compression pressure will be low. A setting that is too
high will result in shock and perhaps damage to the machine.

The compensator valve can fail either open or closed. If the valve fails
open, the pump will be de-stroked to a near 0 GPM flow rate and the
pressure at the outlet port will be very low. If the valve fails closed, the
pump will never de-stroke and will deliver maximum flow at all times.
Whenever the full pump volume is not being used in the machine,
pressure will build to the No. 2A relief valve setting and return to tank

Page 18 Troubleshooting Press Hydraulics

 Prepress No. 3

at high pressure generating heat. If either problem exists, turn the

pump off and make sure the pressure at the outlet port is 0 PSI.
Remove the compensator from the pump and take it apart. Inspect
the hollow orifices in the valve spool for contamination. Make sure
that there is no trash inside the compensator housing. Verify that the
spring is not bent, broken or rusted. Re-assemble the compensator
and attempt to reset the spring to the proper setting.

Oil that bypasses internally across the tight tolerances in the pump
will drain back to tank through the case drain to keep pressure from
building against the shaft seal. As the pump wears, these tolerances
become greater, resulting in higher case flow. Thus case flow will
increase as the pump becomes more worn. The most effective way
to track pump wear is by measuring the amount of case flow. When
the pump is relatively new, case flow should be approximately 1 – 3%
of the total output, or about .2 – .6 GPM. If case flow increases to as
much as 10% of the total pump volume, the pump should be
replaced. The case drain line can be removed and ported into a 5
gallon bucket to check the flow rate. A flow meter can be installed in
the case drain line for convenient regular measurement of case flow.

2 Pump

Troubleshooting Press Hydraulics Page 19

Prepress No. 3

2A Relief Valve
This valve is used as an extreme safety device in the system. In the
event the pump compensator was to fail closed, the valve would open
dumping any excess volume through the valve spool and back to the
tank. The tank line of this valve will be hot if this were to occur. It is
important that this valve be set above the setting of the compensator.
The recommended setting of this relief valve is 250-300 PSI above
the setting of the compensator. Please refer to our Maintenance
Basic Hydraulic Troubleshooting manual, Hydraulic Pumps section
for properly setting the relief valve and pump compensator. If the
relief valve is set below the compensator, then the pump will deliver
maximum volume at all times. This means that any oil that the pump
is delivering that the system does not require will return to tank
through the relief valve spool. Heat will once again be generated
when this occurs. If this valve were to fail in the open position, then
the circuit would operate very slowly or not at all.

2A Relief Valve

Page 20 Troubleshooting Press Hydraulics

 Prepress No. 3

2B Check Valve
The purpose of this check valve is to provide a backpressure of
approximately 65 PSI, which is necessary for shifting the No. 6 main
spool once either of the pilot valve solenoids is energized. If this
check were to fail open because of trash or a broken spring, then
adequate pressure would not build to shift the No. 6 valve.

3 Return Filter
The oil that exhausts out of the No. 6 directional valve’s tank line is
ported through this filter before returning back to the tank. The
element’s condition should be checked regularly if provided with a
visual indicator. The element should also be set up to be changed on
a regular basis. This schedule can be established by an oil analysis
program. If the element plugs up and the inlet pressure reaches the
internal check valve’s setting (25 PSI), dirty oil will bypass the
element.

3 Return Filter

Troubleshooting Press Hydraulics Page 21

Prepress No. 3

3A Heat Exchanger
The oil that exhausts out of the No. 6 directional valve’s tank line is
ported through tubes inside the shell of this heat exchanger before
returning to tank. The water flow is ported through tubes in the
opposite direction. The heat in the oil is transferred from the oil to the
water. To achieve the most efficient heat transfer, the water flow
should be 25% of the oil flow. The water flow can be controlled by
manual valves, a water modulating valve or an electrical solenoid
valve.

Circulating hot wash oil or light distillate through the tube side or shell
side will usually effectively remove sludge or similar soft deposits.
Soft salt deposits may be washed out by circulating hot fresh water.
Some cleaning compounds such as “Oakite” or Dowell” may be
effective in removing more stubborn deposits.

3A Heat Exchanger

Page 22 Troubleshooting Press Hydraulics

 Prepress No. 3

6 Directional Valve
To close the prepress, a voltage is applied to the “A” coil on the pilot
valve. Pilot pressure is directed internally into one side of the main
spool. The main spool then shifts into the “straight arrows” position.
Flow from the pump flows through the “P” and “A” ports then into the
full piston side of the jack ram. The oil in the rod side is forced out and
returns to the tank through the No. 8 flow control valve and the “B”
and “T” ports of this valve. The valve is maintained in the “A” position
in the “close prefills”, “pressurize main rams” and “compression”
cycles. Both solenoids are de-energized in the “decompression”
cycle.

To open the prepress, a

voltage is applied to the “B”
coil on the pilot valve. Pilot
pressure is directed internally
into one side of the main spool.
The main spool then shifts into
the “crossed arrows” position.
Flow from the pump flows
through the “P” and “B” ports
then into the rod side of the
jack ram. The oil in the full
piston side is forced out and
returns to the tank through the
6 Directional Valve
“A” and “T” ports.

This valve is a tandem center, three position, four way, double

solenoid, externally piloted, internally drained, spring centered
directional control. When replacing the valve, make sure the part
numbers match exactly as one letter or one number may mean that
the new valve has a different piloting and draining arrangement or a
different spool.

Troubleshooting Press Hydraulics Page 23

Prepress No. 3

7 Directional Valve
This valve is mechanically actuated by the platen if a short stack or no
stack is in the prepress. The valve shifts open when actuated,
allowing the pump flow to vent back to the tank. Pressure will not
build up when this occurs. This is a normally closed, two position, two
way, mechanically actuated, spring return directional valve.

7 Directional Valve

8 Flow Control
This valve controls the speed at which the prepress closes. Care
should be taken not to close the valve too much, as this will create a
backpressure at the inlet of the jack ram. If the No. 10 check valve
setting (100 PSI) is reached before the platen contacts the stack of
veneer, the check valve will open, directing pilot pressure to close the
No. 13 prefill valves. Pressure will then continue building until the No.
9 sequence valve setting is reached. The pump flow will then begin
filling the main rams too soon. A very slow compression would be the
result. When opening the prepress, the oil will flow through the
internal bypass check valve.

Page 24 Troubleshooting Press Hydraulics

 Prepress No. 3

9 Sequence Valve
This valve must be set above the pressure required to close the
prepress. When the setting of the sequence valve is reached, the
pump flow is directed through the valve to pressurize the main rams.
If the valve sticks open, the pump volume will flow into the rams and
return to tank through the No. 13 prefill valves.

9 Sequence Valve & 12 Pilot Operated Check Valve

10 Check Valve
Once the platen contacts
the veneer, pressure will
build to the setting of the
spring, 100 PSI. The valve
then opens, directing
pressurized fluid to shift
the prefill valves closed.

10 Check Valve

Troubleshooting Press Hydraulics Page 25

Prepress No. 3

11 Check Valve
The No. 6 directional valve will de-energize when the compression
timer elapses. Pressurized fluid in the main rams will then bleed
through this check valve and back to tank through the “P” and “T”
ports of the directional valve main spool.

12 Pilot Operated Check Valve

When the No. 6 directional valve is energized in the “B” position to
open the prepress, pilot pressure is also directed to shift this check
valve open. Pressurized pilot fluid to the No. 13 prefill valves is ported
back to tank through this pilot operated check valve. The prefill valves
will then shift open connecting the oil in the main rams back to the
reservoir. If this check valve sticks open, the pilot pressure will not
build to close the prefill valves. The prepress will not go into the
compression mode if this occurs.

13 Prefill Valves
When closing the prepress, the
prefill valves are open allowing oil
flow from the reservoir to the main
rams. When the platen contacts
the stack, the pressure will build
first to the No. 10 check valve
setting, then to the No. 9 sequence
valve setting. The No. 10 valve will
then open, directing pilot pressure
to close the prefill valves. When the
No. 6 directional valve energizes in 13 Prefill Valves
the “B” position to open the
prepress, the No. 12 pilot operated check valve shifts open. Pilot
pressure in the prefill valve pilot lines is bled to tank through the No.
12 check valve. The prefill valves again shift open, hydraulically
connecting the main rams to the reservoir. As the prepress opens, oil
in the main rams returns to tank through the prefill valves. If a prefill
valve fails, pressure in the rams may build slowly or not at all.

Page 26 Troubleshooting Press Hydraulics

 Prepress No. 3

14 Pressure Switch
This switch is used to send a signal to start the compression timer.

Check Valves

Troubleshooting Press Hydraulics Page 27

Prepress No. 3

Page 28 Troubleshooting Press Hydraulics

 Prepress No. 3

Troubleshooting Press Hydraulics Page 29

Prepress No. 3

Page 30 Troubleshooting Press Hydraulics

 Prepress No. 3

Troubleshooting Press Hydraulics Page 31

Prepress No. 3

Page 32 Troubleshooting Press Hydraulics

 Prepress No. 3

Troubleshooting Press Hydraulics Page 33

Prepress No. 3

Page 34 Troubleshooting Press Hydraulics

 Hot Presses No. 1 & 2

Hot Presses No. 1 & 2

Symbol Description
FM Flow Meter
This flow meter will indicate the water flow rate through the No. 26
heat exchanger.

NC Hand Valve
This valve may be opened when necessary to dump the No. 2 pump
volume to tank.

PT Pressure Transducer
This transducer converts the pressure in the main rams into a
proportional milliamp signal. A 4-20 mA signal is normally used to
indicate the pressure. As of the writing of this manual, no electrical
information was given for the function of PT. The transducer may
perform the same function as the No. 30 pressure switch or give a
warning if the pressure is below a preset pressure indicating a
low-pressure condition exists during the “compression” cycle.

PT Pressure Transducer

Troubleshooting Press Hydraulics Page 35

Hot Presses No. 1 & 2

SP Pump
The purpose of the pump is to port any bypassing past the ram seals
back to the reservoir.

1 Pump
This is a fixed displacement, piston
type, high volume pump. The pump
volume is dumped back to tank at low
pressure through the No. 5 directional
valve when in the Idle Mode. When
the Press Close cycle is initiated, the
solenoid is energized directing pilot
pressure to shift the No. 5 main spool
closed. The pump volume combines 1 Pump
with the No. 2 pump flow and is ported
into the jack rams. The pump will continue to deliver oil to the system
until the solenoid on valve No. 5 is de-energized. A pressure switch is
usually actuated to de-energize the solenoid. At that time the No. 5
spool will spring return to the open position. The pump volume once
again returns to tank at low pressure.

One check that can be made to verify that the pump is badly worn is to
remove the eyebolt from the top of the housing. If oil is pouring out of
the hole then the pump is excessively bypassing. Another check that
can be made is the electric motor current. When the pump is
bypassing a lower current reading will be indicated. The third check
that can be made is to open the NC hand valve connected in the No. 2
pump outlet line. Manually or electrically actuate the “A” solenoid on
the no. 4 valve and the no. 5 pilot valve. The no. 1 pump volume will
then flow into the jack rams. Record the amount of time that it takes
the jack rams to move a specific distance or to close the press. An
initial test should be made to establish a reference. Make sure there
is no oil flowing through the No. 1A or No. 5 valves when this test is
made. This can be checked by checking the temperature of the No.
1A and No. 5 valves’ tank lines as the press closes. The tank lines
should not increase in heat in this mode.

Page 36 Troubleshooting Press Hydraulics

 Hot Presses No. 1 & 2

1A Relief Valve
This valve limits the maximum pressure to the No. 1 high volume
pump. The valve should be set at least 200 PSI above the pressure
that the pump unloads. The No. 1 pump will pressurize the rams until
the No. 5 solenoid is de-energized. The pressure that the solenoid
de-energizes is the maximum pressure in the No. 1 pump line.

If this valve were to stick partially or fully open then the press would
close slower than normal. The valve is located on the No. 1 high
volume pump.

1A Relief Valve

2 Pump
This is a variable displacement, externally drained, remote pressure
compensating type piston pump. The pump will deliver maximum
volume to the press until the No. 7 valve setting is reached. The No. 7
remote relief valve will then shift open and direct oil to the
compensator piston inside the pump. The compensator will move
the internal slideblock which reduces the pump’s volume. The pump
will then deliver only enough oil to maintain the No. 7 setting when
compensating.

Troubleshooting Press Hydraulics Page 37

Hot Presses No. 1 & 2

A stroke indicator on the pump will visually indicate the amount the
pump is stroked. A dial indicator or scale can measure the stroke
indicator movement. When the pin is pulled all the way in, the pump is
delivering maximum volume. When the center groove is aligned with
the pump housing, the pump is delivering a near 0 GPM flow rate.

Another check that can be made is to close the press with this pump
only and record the amount of time until mat contact. This test should
be made initially when the pump is new or operating properly to
establish a reference. Another test to make is to record the motor
current when closing the press. The electric motor will only “pull”
enough electrical current to drive the pump. If the pump is
excessively worn and is bypassing then the electrical current will be
at a lower level. The eyebolt on top of the pump can be removed to
determine if the pump is badly worn. If a constant flow is observed
then the pump is excessively bypassing. The manual volume stop
located on the pressure compensator side of the pump should be set
to allow maximum volume out of the pump when making the above
tests. Turning the adjustment counter clockwise permits the pump
volume to increase if set below maximum. The volume stop on the
opposite side of the housing is preset to prevent the pump from
delivering oil to the “B” port. Since the “B” port on the pump is
plugged, this stop should not be adjusted.

2 Pump “A” Side 2 Pump “B” Side

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 Hot Presses No. 1 & 2

2A Relief Valve
The valve is mounted on the side of the No. 2 pump and is used to
limit the maximum pressure when the press is closing. The valve is
preset by Oilgear to 3000 PSI. Normally oil should not flow over this
relief valve. This valve must be set above the No. 7 remote
compensator valve setting. If this valve fails open, then the closing
and compression of the rams may be slower or maximum pressure
may not be reached. The valve can be removed from the housing
and checked for trash or wear.

2B Pump
This 7.23 GPM, fixed displacement, gear type pump is mounted
inside the No. 2 housing. The pump performs three functions in the
system:

1) Supplies pilot fluid to all of the hydraulic piloted valves (Nos.

4, 5, and 6). Pilot pressure to the valves will be at the No. 2C
relief valve setting. The pilot oil is directed out of port No. 27 on
the pump (see “D pump stroked to A port” picture for port
connections).

2) Supplies additional pump flow to the suction of the No. 2

main pump. In the compression modes, the gear pump will
deliver more volume than the No. 2 pump requires. The excess
oil will return to tank through the No. 2E relief valve.

3) Supplies oil from port 12 through a filter and heat exchanger

for cooling the oil and returning through port 25 prior to being
directed to the suction port of the No. 2 main pump (see “D
pump stroked to A port” picture for port connections).

To check this pump, insert a tee in the pilot pressure line. In the
bottom of the tee connect a needle valve and a hose. Run the hose
into a container of known size. Fully open the needle valve then turn

Troubleshooting Press Hydraulics Page 39

Hot Presses No. 1 & 2

the no. 2 and 2B pump on. Turn the needle valve handle CW until the
pilot pressure gauge reads 50 PSI. Approximately 7 ¼ GPM should
flow into the bucket in one minute’s time. If a flow rate significantly
below this is recorded then the pump is most likely bad.

2C Relief Valve
The setting (85 PSI) of this valve determines the pilot pressure to shift
the Nos. 4, 5, and 6 valves. The valve is located on the front of the
main pump and is a hex head cartridge type valve. This valve
commonly gets contaminated which results in a low pilot pressure.
The valve can be removed and checked if this condition were to
occur.

2D Check Valve
This valve permits free flow from the reservoir to the pump when the
No. 2 pump requires more volume than supplied by pump No. 2B.
When in compression the No. 2 pump is compensating and only
requires a low volume. The check valve will then block the No. 2B
pump flow back to the reservoir, forcing the gear pump oil into the
pump suction. The excess volume supplied by the No. 2B pump will
dump over the No. 2E relief valve. The check valve is mounted in a
block on the bottom of the No. 2 pump.

2E Relief Valve
The setting of this valve (35 PSI) determines the pressure on the
suction side of the No. 2 pump. When the No. 2 pump requires less
oil than the No. 2B pump delivers, the excess oil will dump over this
relief valve. The valve is mounted in the same block as the No. 2D
check valve, which is located on the underside of the No. 2 pump.

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 Hot Presses No. 1 & 2

2F Relief Valve
This valve limits the pressure to the pump compensator piston. The
valve setting is approximately 170 PSI. If the valve fails open then the
pump will deliver maximum volume at all times. The excess pump
volume would return to tank through the No. 2A relief valve. This will
cause the system to eventually overheat. The valve is located in a
block on the side of the compensator housing. The housing can be
removed and the valve checked for contamination and bad springs.

3 Prefill (Surge) Valve

The prefill valve is a large valve mounted in the press pit. The valve
spool is shifted by a hydraulic actuator. When the press is closing the
valve hydraulically connects the four main rams to the reservoir. As
the pumps supply fluid to the jack rams when closing the press oil free
flows or “prefills” the main rams. When the press reaches the top and
the pressure builds to the No. 3B valve setting, oil is ported to the full
piston side of the prefill valve actuator. As the actuator extends, the
prefill valve spool is shifted. Once shifted, the spool directs high
pressure fluid from the pumps to pressurize the four main rams.

The spool will remain shifted until the decompression mode. The “B”
solenoid on the No. 4 directional valve energizes in Decompression
directing the pump flow to the rod side of the actuator. Pressure in the
full piston side is gradually bled down through the No. 3C needle
valve. Initially the actuator will remain extended because the
pressure on the full piston side acts on a greater square inch area
(Force = PSI x Area). When the pressure on the full piston side
bleeds down so that more force is developed on the rod side, the
actuator will retract. The fluid in the main rams is once again
hydraulically connected to the reservoir by the valve spool.

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Hot Presses No. 1 & 2

3A Flow Control
This valve is piped off of the surge valve, which is located in the press
pit. The purpose of the valve is to slow the No. 3 actuator piston down
before it fully bottoms out. This prevents the piston from slamming.
Oil will free flow through the internal check valve when initially
retracting the actuator.

3B Sequence Valve
This valve should be set to shift open when the last platen reaches
the top. When the valve opens, pressurized fluid is ported to shift the
prefill (surge) valve actuator. The prefill valve shifts and hydraulically
connects the pumps to pressurize the inner rams. If the valve is
thought to be faulty and not shifting, the No. 20A manual valve can be
opened to bypass it. The sequence valve is located on the prefill
valve itself. If the valve sticks in the open position then the prefill valve
will be shifted before the jack rams reach the top. This will cause the
press to close very slowly.

3C Needle Valve
The setting of this valve determines the retract speed of the prefill
valve actuator when the cylinder piston blocks port No. 7 (The
connection in the middle of the actuator barrel). The adjustment
should be set so the valve opens smoothly to reduce the shock in the
system when opening the prefill valve. The valve is located on the
prefill valve itself.

3D Check Valve
This check valve prevents oil from flowing into the prefill valve
actuator when the system pressure is below the No. 3B setting.
When opening the prefill valve after Decompression, the check
permits free flow out of the full piston side of the actuator, through the
needle valve, and back to tank.

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 Hot Presses No. 1 & 2

4 Directional Valve
In the Idle Mode, both solenoids are de-energized maintaining the
valve spool in the “reverse float” position. Flow from the No. 2 high
pressure pump is directed back to tank through the valve spool. The
oil will recirculate through the spool and back to tank through the “P”
to “T” ports of this directional valve.

To close the press, the “A” solenoid is energized. Pilot pressure from
the No. 2B pump is ported to shift the main spool into the “A” position.
Oil is then directed through the “P” to “A” ports of the valve and to the
jack rams. The valve solenoid will remain energized until the 2nd nd

Stage Compression timer elapses. When the “B” solenoid energizes

to start the Decompression Mode, pilot pressure from the No. 2B
gear pump shifts the spool into the “B” position. The pump flow is
ported to the rod side of the No. 3 prefill valve actuator when in the “B”
position. No. 4 is a three position, four way, solenoid controlled,
externally piloted and drained, spring centered, directional valve.

4 Directional Valve

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Hot Presses No. 1 & 2

5 Directional Valve
In the Idle Mode of operation the
solenoid is de-energized
permitting the No. 1 pump
volume to return to tank at low
pressure. When the Close cycle
is initiated, the solenoid
energizes directing pilot
pressure from the No. 2B pump
to shift the main spool closed.
The speed that the spool shifts
is determined by the No. 23B
needle valve setting. The No. 1 5 Directional Valve
pump will then deliver oil to the
jack rams. When the last platen
reaches the top, the solenoid is de-energized. A pressure switch may
be used to de-energize the coil. The No. 5 main spool returns back to
the open position again dumping the No. 1 pump volume. No. 5 is a
normally open, two position, two way, solenoid controlled, spring
return, externally hydraulically piloted and drained directional valve.

6 Directional Valve
When the high compression timer elapses, the pilot solenoid on this
valve energizes. Pilot pressure is then directed to shift the main
spool into the open position. Pressure from the rams is directed to
the No. 8 remote compensator
valve. The No. 2 pump will now
only supply enough oil to maintain
the valve’s pressure setting. No.
6 is a normally closed, two
position, two way, single solenoid
controlled, externally piloted and
drained, spring return, directional
valve.

6 Directional Valve

Page 44 Troubleshooting Press Hydraulics

 Hot Presses No. 1 & 2

7 Remote Compensator Valve

The No. 2 pump will deliver maximum volume to the press rams until
the No. 7 valve setting is reached. At that time the valve shifts open
and directs pressurized fluid to the pump compensator. The No. 2
pump will then de-stroke and deliver only enough oil to maintain the
No. 7 valve setting. The setting of this valve determines the High
Compression pressure. If this valve were to fail open then a low
pressure (170 PSI) will be indicated once the prefill valve shifts.

7 & 8 Remote Compensator Valves

8 Remote Compensator Valve

The setting of this valve determines the low compression pressure of
the press. When the high pressure timer elapses, the No. 6 solenoid
energizes to direct pressure in the rams to the valve. The pump will
now only deliver enough oil to maintain the spring setting of the valve.

Troubleshooting Press Hydraulics Page 45

Hot Presses No. 1 & 2

9 Pressure Reducing Valve

The purpose of this valve is to
provide for a constant opening
speed of the press. The pressure
on both sides of the No. 16A flow
control is sensed on opposite
sides of the reducing valve spool.
The valve will maintain a constant
pressure drop across the No. 16A
flow control. Flow through the flow
control will be the same regardless
of the pressure exerted by the
9 Pressure Reducing Valve
weight of the press. As the platens
drop off when the press opens, the
pressure exerted by the weight of the press will change. The valve
spool will shift in response to the pressure changes maintaining a
constant flow through No. 16A.

10 Relief Valve
When in the Decompression
Mode, this relief valve setting
determines the pressure to the
rod side of the prefill valve
actuator. When the No. 4 “B”
solenoid energizes to start
Decompression, the actuator will
not immediately retract because
of the pressure on the full piston
side of the cylinder. The pressure
on the full piston side will 10 Relief Valve
gradually bleed down through the
Nos. 3C, 3D, 23A and 4 valves.
When the hydraulic force on the rod side of the actuator is greater
than on the full piston side, the actuator will retract. The relief valve
must shift closed in order to retract the actuator.

Page 46 Troubleshooting Press Hydraulics

 Hot Presses No. 1 & 2

11 Check Valve
This valve permits free flow in one direction when decompressing but
blocks the flow in the opposite direction when closing the press.

Valves 11 & 24

12A Check Valve

This valve permits free flow to the No. 3 prefill and No. 3B sequence
valves. It will block the oil flow in the reverse direction.

12B Check Valve

This valve permits free flow from the pump to the jack rams when
closing the press. The valve will block the oil in the reverse direction
when the press is opening, which forces the oil through the No. 9 and
16A valves.

12A, 12B & 23A

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Hot Presses No. 1 & 2

14 Filter
The excess No. 2 pump volume not required for pilot pressure will
flow through the No. 2C relief valve. The oil is then directed through
this filter element, the heat exchanger and into the No. 2 pump
suction. The element condition should be checked regularly and
changed as necessary.

14 Filter

16A Needle Valve

The setting of this valve determines the lowering speed of the press.
The oil in the jack rams will flow through this valve before returning to
the tank through the No. 4 directional valve. Rotating the adjustment
clockwise reduces the opening speed of the press. If this valve were
to become contaminated then the press would open at a slower
speed. Many times this problem can be solved by rotating the valve
adjustment counterclockwise, 2 – 3 turns. Always set the valve back
to its original setting.

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 Hot Presses No. 1 & 2

16B Manual Valve

During the normal operation of
the press cycle, this valve is in
the closed condition. When
necessary to manually open the
press, this valve should be
open. The oil in the jack rams
and main rams will return to tank
through this manual valve.
While the press is operating
under normal conditions, the
tank line of this valve should be
cold or cool.
16B Manual Valve
17 Needle Valve
When the No. 4B solenoid is
energized in decompression,
the No. 9 pressure reducing
valve will start shifting toward
the closed position. The rate
that it shifts partially closed is
controlled by this needle valve.
If this needle valve were to plug
up with contamination then the
lowering speed of the press
may be affected. The press
would gradually slow down as it
reaches bottom if this valve
were contaminated. The valve
should be adjusted so that the 17 Needle Valve
press does not “jump” when the
decompression cycle begins.

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Hot Presses No. 1 & 2

18A Manual Valve

This valve is used to bleed the air out of the main rams after
performing maintenance. By opening this valve a flow path will exist
from the oil in the main rams through the No. 25 sight glass and back
to tank. When air is in the oil foaming will be seen. Once the air is
bled out the oil color will return to a light brown. At that time this valve
should be closed.

18A, 18B & 25

18B Manual Valve

This valve is used to bleed the air out of the jack rams after
performing maintenance. By opening this valve a flow path will exist
from the oil in the main rams through the No. 25 sight glass and back
to tank. When air is in the oil foaming will be seen. Once the air is
bled out the oil color will return to a light brown. At that time this valve
should be closed.

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 Hot Presses No. 1 & 2

19 Manual Valve
This valve is used to isolate the pressure gauge. The No. 28 gauge is
located on the operator’s console. When necessary to remove and
replace the gauge this hand valve should be closed.

20A Manual Valve

During normal operation of the press, this valve is in the closed
position. The purpose of the valve is to provide a bypass around the
No. 3B sequence valve when necessary to shift the prefill valve
spool. This may be used to shift the prefill after replacing the ram
seals or when troubleshooting the No. 3B valve. If the No. 3B valve
were to stick closed then the prefill valve would not shift and the main
rams will not pressurize. By opening this valve, it allows the oil to flow
into the full piston side of the prefill valve actuator permitting it to shift
into the closed position.

20B Manual Valve

This valve is used when necessary to drain the oil out of the main
rams. A hose or pipe should be connected to this valve and run into a
container or back into the reservoir.

21 Manual Valve
This valve is located near the bottom of the reservoir. This valve can
be used when necessary to drain the oil out of the tank.

22 Check Valve
This check valve is used to block flow from the reservoir to the No. 4
directional valve when necessary to change the valve.

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Hot Presses No. 1 & 2

23A Needle Valve

The setting of this valve (and valve No. 24) determines the rate at
which the press decompresses. The oil in the full piston side of the
prefill valve actuator and the oil in the main rams will bleed through
this needle valve before returning back to the tank. If the press takes
too long in decompression, this valve may be contaminated. Many
times by rotating the adjustment 2 – 3 turns counterclockwise, the
trash will be blown through the valve.

23B Needle Valve

This valve functions as a “pilot choke” and controls the rate at which
the No. 5 directional valve spool shifts closed.

23C Needle Valve

This valve functions as a “pilot choke” and controls the rate at which
the No. 6 directional valve spool shifts open.

24 Needle Valve
This valve (along with No. 23A) is used to meter the oil out of the main
rams in the decompression cycle. The setting of these two valves
controls the rate at which the rams decompress. If the press takes
too long in the decompression cycle then either No. 23A or 24 may be
contaminated. By manually rotating the adjustment
counterclockwise, 2 – 3 turns the pressure will many times blow the
trash through the valves. Be certain to reset the valves to its original
setting.

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 Hot Presses No. 1 & 2

25 Sight Glass
When necessary to bleed oil out of the main and jack rams, the No.
18A and 18B manual valves will be open. Oil in the rams is then
ported through this sight glass. The oil color will be foamy when air is
present. Once the color returns to a light brown, this means that the
air has been bled out of the rams. The No. 18A and 18B manual valve
should be closed after bleeding the air out of the rams.

26 Cooler
The No. 2B gear pump volume is ported through this water cooler
prior to entering the No. 2 pump suction. There should be a 10 – 15
0 0

difference between the inlet and outlet water lines when the cooler is
operating properly.

26 Cooler

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Hot Presses No. 1 & 2

27 Fixed Orifice
This is sometimes called a gauge saver or snubber. Its purpose is to
protect the pressure gauge from pressure spikes.

28 Gauge
This gauge is located on the operator’s console. It will only read
pressure once the No. 3 prefill valve spool is shifted.

29 Press Recorder
The pressure in the main rams will be indicated on the graph of this
recorder.

30 Pressure Switch
This switch may be used for one of two purposes. The first is to
de-energize the No. 5 solenoid valve when the setting is reached.
This would permit the No. 1 pump volume to flow back to tank through
the No. 5 valve at low pressure. The switch may also be used to start
the high pressure timer once its setting is reached.

30 Pressure Switch

Page 54 Troubleshooting Press Hydraulics

 Hot Presses No. 1 & 2

1 Pump Isolation Check Valve

Hot Press 1 & 2 Surge Valve

Troubleshooting Press Hydraulics Page 55

Hot Presses No. 1 & 2

C Pump

C Pump Cutaway

Page 56 Troubleshooting Press Hydraulics

 Hot Presses No. 1 & 2

D Pump Remote Compensator Control

Troubleshooting Press Hydraulics Page 57

Hot Presses No. 1 & 2

D Pump Stroked to “A” Port

Page 58 Troubleshooting Press Hydraulics

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Troubleshooting Press Hydraulics Page 67
 Hot Press No. 3

Hot Press No. 3

Symbol Description
FM Flow Meter
This flow meter will indicate the water flow rate through the No. 26
heat exchanger.

PT Pressure Transducer
This transducer converts the pressure in the main rams into a
proportional milliamp signal. A 4-20 mA signal is normally used to
indicate the pressure. As of the writing of this manual, no electrical
information was given for the function of PT. The transducer may
perform the same function as the No. 30 pressure switch or give a
warning if the pressure is below a preset pressure indicating a
low-pressure condition exists during the “compression” cycle.

PT Pressure Transducer

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Hot Press No. 3

SP Pump
The purpose of this pump is to port any bypassing past the ram seals
back to the reservoir.

1 Pump
This is a fixed displacement, piston type, high volume pump. The
pump volume is dumped back to tank at low pressure through the No.
5 directional valve when in the Idle Mode. When the Press Close
cycle is initiated, the solenoid is energized directing pilot pressure to
shift the No. 5 main spool closed. The pump volume combines with
the No. 2 pump flow and is ported into the jack rams. The pump will
continue to deliver oil to the system until the solenoid on valve No. 5 is
de-energized. A pressure switch is usually actuated to de-energize
the solenoid. At that time the No. 5 spool will spring return to the open
position. The pump volume once again returns to tank at low
pressure.

One check that can be made to verify that the pump is badly worn is to
remove the eyebolt from the top of the housing. If oil is pouring out of
the hole then the pump is excessively bypassing. Another check that
can be made is the electric motor current. When the pump is
bypassing a lower current reading will be indicated. The third check
that can be made is to open the NC hand valve connected in the No. 2
pump outlet line. Manually or electrically actuate the “A” solenoid on
the no. 4 valve and the no. 5 pilot valve. The no. 1 pump volume will
then flow into the jack rams. Record the amount of time that it takes
the jack rams to move a specific distance or to close the press. An
initial test should be made to establish a reference. Make sure there
is no oil flowing through the No. 1A or No. 5 valves when this test is
made. This can be checked by checking the temperature of the No.
1A and No. 5 valves’ tank lines as the press closes. The tank lines
should not increase in heat in this mode.

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 Hot Press No. 3

1A Relief Valve
This valve limits the maximum pressure to the No. 1 high volume
pump. The valve should be set at least 200 PSI above the pressure
that the pump unloads. The No. 1 pump will pressurize the rams until
the No. 5 solenoid is de-energized. The pressure that the solenoid
de-energizes is the maximum pressure in the No. 1 pump line.

If this valve were to stick partially or fully open then the press would
close slower than normal. The valve is located on the No. 1 high
volume pump.

1A Relief Valve

2 Pump
This is a variable displacement, externally drained, remote pressure
compensating type piston pump. The pump will deliver maximum
volume to the press until the No. 7 valve setting is reached. The No. 7
remote relief valve will then shift open and direct oil to the
compensator piston inside the pump. The compensator will move
the internal slideblock which reduces the pump’s volume. The pump
will then deliver only enough oil to maintain the No. 7 setting when
compensating.

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Hot Press No. 3

A stroke indicator on the pump will visually indicate the amount the
pump is stroked. A dial indicator or scale can measure the stroke
indicator movement. When the pin is pulled all the way in, the pump is
delivering maximum volume. When the center groove is aligned with
the pump housing, the pump is delivering a near 0 GPM flow rate.

Another check that can be made is to close the press with this pump
only and record the amount of time until mat contact. This test should
be made initially when the pump is new or operating properly to
establish a reference. Another test to make is to record the motor
current when closing the press. The electric motor will only “pull”
enough electrical current to drive the pump. If the pump is
excessively worn and is bypassing then the electrical current will be
at a lower level. The eyebolt on top of the pump can be removed to
determine if the pump is badly worn. If a constant flow is observed
then the pump is excessively bypassing. The manual volume stop
located on the pressure compensator side of the pump should be set
to allow maximum volume out of the pump when making the above
tests. Turning the adjustment counter clockwise permits the pump
volume to increase if set below maximum. The volume stop on the
opposite side of the housing is preset to prevent the pump from
delivering oil to the “B” port. Since the “B” port on the pump is
plugged, this stop should not be adjusted.

2 Pump “A” Side 2 Pump “B” Side

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 Hot Press No. 3

2A Relief Valve
The valve is mounted on the side of the No. 2 pump and is used to
limit the maximum pressure when the press is closing. The valve is
preset by Oilgear to 3000 PSI. Normally oil should not flow over this
relief valve. This valve must be set above the No. 7 remote
compensator valve setting. If this valve fails open, then the closing
and compression of the rams may be slower or maximum pressure
may not be reached. The valve can be removed from the housing
and checked for trash or wear.

2B Pump
This 7.23 GPM, fixed displacement, gear type pump is mounted
inside the No. 2 housing. The pump performs three functions in the
system:

1) Supplies pilot fluid to all of the hydraulic piloted valves (Nos. 4, 5,

and 6). Pilot pressure to the valves will be at the No. 2C relief valve
setting. The pilot oil is directed out of port No. 27 on the pump (see
“D pump stroked to A port” picture for port connections).

2) Supplies additional pump flow to the suction of the No. 2 main

pump. In the compression modes, the gear pump will deliver more
volume than the No. 2 pump requires. The excess oil will return to
tank through the No. 2E relief valve.

3) Supplies oil from port 12 through a filter and heat exchanger for
cooling the oil and returning through port 25 prior to being directed
to the suction port of the No. 2 main pump (see “D pump stroked to
A port” picture for port connections).

To check this pump, insert a tee in the pilot pressure line. In the
bottom of the tee connect a needle valve and a hose. Run the hose
into a container of known size. Fully open the needle valve then turn
the no. 2 and 2B pump on. Turn the needle valve handle CW until the

Troubleshooting Press Hydraulics Page 72

Hot Press No. 3

pilot pressure gauge reads 50 PSI. Approximately 7 ¼ GPM should

flow into the bucket in one minute’s time. If a flow rate significantly
below this is recorded then the pump is most likely bad.

2C Relief Valve
The setting (85 PSI) of this valve determines the pilot pressure to shift
the Nos. 4, 5, and 6 valves. The valve is located on the front of the
main pump and is a hex head cartridge type valve. This valve
commonly gets contaminated which results in a low pilot pressure.
The valve can be removed and checked if this condition were to
occur.

2D Check Valve
This valve permits free flow from the reservoir to the pump when the
No. 2 pump requires more volume than supplied by pump No. 2B.
When in compression the No. 2 pump is compensating and only
requires a low volume. The check valve will then block the No. 2B
pump flow back to the reservoir, forcing the gear pump oil into the
pump suction. The excess volume supplied by the No. 2B pump will
dump over the No. 2E relief valve. The check valve is mounted in a
block on the bottom of the No. 2 pump.

2E Relief Valve
The setting of this valve (35 PSI) determines the pressure on the
suction side of the No. 2 pump. When the No. 2 pump requires less
oil than the No. 2B pump delivers, the excess oil will dump over this
relief valve. The valve is mounted in the same block as the No. 2D
check valve, which is located on the underside of the No. 2 pump.

2F Relief Valve
This valve limits the pressure to the pump compensator piston. The
valve setting is approximately 170 PSI. If the valve fails open then the
pump will deliver maximum volume at all times. The excess pump
volume would return to tank through the No. 2A relief valve. This will

Page 73 Troubleshooting Press Hydraulics

 Hot Press No. 3

cause the system to eventually overheat. The valve is located in a

block on the side of the compensator housing. The housing can be
removed and the valve checked for contamination and bad springs.

3 Prefill (Surge) Valve

The surge valve is a large valve mounted in the press pit. The valve
spool is shifted by a hydraulic actuator. When the press is closing the
valve hydraulically connects the four main rams to the reservoir. As
the pumps supply fluid to the outside rams when closing the press oil
free flows or “prefills” the main rams. When the press reaches the top
and the pressure builds to the No. 3B valve setting, oil is ported to the
full piston side of the prefill valve actuator. As the actuator extends,
the prefill valve spool is shifted. Once shifted, the spool directs fluid
to pressurize the four main rams.

The spool will remain shifted until the decompression mode. The “B”
solenoid on the No. 4 directional valve energizes in Decompression
directing the pump flow to the rod side of the actuator. Pressure in the
full piston side is gradually bled down through the No. 3C needle
valve. Initially the actuator will remain extended because the
pressure on the full piston side acts on a greater square inch area
(Force = PSI x Area). When the pressure on the full piston side
bleeds down so that more force is developed on the rod side, the
actuator will retract. The fluid in the main rams is once again
hydraulically connected to the reservoir by the valve spool.

3A Flow Control
This valve is piped off of the surge valve, which is located in the press
pit. The purpose of the valve is to slow the No. 3 actuator piston down
before it fully bottoms out. This prevents the piston from slamming.
Oil will free flow through the internal check valve when initially
retracting the actuator.

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3B Sequence Valve
This valve should be set to shift open when the last platen reaches
the top. When the valve opens, pressurized fluid is ported to the
prefill valve actuator. The prefill valve shifts and hydraulically
connects the pumps to pressurize the inner rams.

3C Flow Control
The setting of this valve determines the retract speed of the prefill
valve actuator. The adjustment should be set so the valve opens
smoothly to reduce the shock in the system when opening the prefill
valve.

3D Check Valve
As the prefill valve actuator retracts, oil is directed through the No. 3C
needle valve to control its speed. This check valve will allow the flow
to bypass the No. 3B sequence valve at this time. It will block the flow
through No. 3C when the prefill valve actuator extends, forcing it to
travel only through the No. 3B sequence valve. If this check valve
should fail open, the prefill valve will shift before pressure has built to
the No. 3B sequence valve setting and slow the operation of the
press.

4 Directional Valve
In the Idle Mode, both solenoids are de-energized. Internal springs
hold the valve spool shifted into the “tandem center” position. Flow
from the No. 2 high pressure pump is directed back to tank through
the valve spool. The oil will re-circulate through the spool and back to
tank through the “P” to “T” ports of this directional valve.

To close the press, the “A” solenoid is energized. Pilot pressure from
the No. 2B pump is ported to shift the main spool into the “A” position.
Oil is then directed through the “P” and “A” ports of the valve to the
jack rams. The valve solenoid will remain energized until the 2nd nd

Stage Compression timer elapses. When the “B” solenoid energizes

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 Hot Press No. 3

to start the Decompression

Mode, pilot pressure from the
No. 2B gear pump shifts the
spool into the “B” position.
The pump flow is ported to
the rod side of the No. 2 prefill
valve actuator when in the “B”
position. No. 4 is a three
position, four way, tandem
center, solenoid controlled,
externally piloted and
drained, spring centered,
directional valve.
4 Directional Valve

5 Directional Valve
In the Idle Mode of operation
the solenoid is de-energized
permitting the No. 1 pump
volume to return to tank at
low pressure. When the
Close cycle is initiated, the
solenoid energizes directing
pilot pressure from the No.
2B pump to shift the main
spool closed. The speed that
the spool shifts is determined
by the “pilot choke” located
between the pilot valve and 5 Directional Valve
main spool. The No. 1 pump
will then deliver oil to the jack rams. The No. 30 pressure switch is
used to de-energize the coil. The No. 5 main spool returns back to
the open position again dumping the No. 1 pump volume. No. 5 is a
normally open, two position, two way, solenoid controlled, spring
return, externally hydraulically piloted and drained directional valve.

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6 Directional Valve
When the high compression timer elapses, the pilot solenoid on this
valve energizes. Pilot pressure is then directed to shift the main
spool into the open position. Pressure from the rams is directed to
the No. 8 remote compensator valve. The No. 2 pump will now only
supply enough oil to maintain the valve’s pressure setting. No. 6 is a
normally closed, two position, two way, single solenoid controlled,
externally piloted and drained, spring return, directional valve.

6 Directional Valve

7 Remote Compensator Valve

The No. 2 pump will deliver maximum volume to the press rams until
the No. 7 valve setting is reached. At that time the valve shifts open
and directs pressurized fluid to the pump compensator. The No. 2
pump will then de-stroke and deliver only enough oil to maintain the
No. 7 valve setting. The setting of this valve determines the High
Compression pressure. If this valve were to fail open then a low
pressure (170 PSI) will be indicated once the prefill valve shifts.

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8 Remote Compensator Valve

The setting of this valve determines the low compression pressure of
the press. When the high pressure timer elapses, the No. 6 solenoid
energizes to direct pressure in the rams to the valve. The pump will
now only deliver enough oil to maintain the spring setting of the valve.

7 & 8 Remote Compensator Valves

9 Pressure Reducing Valve

The purpose of this valve is to provide for a constant opening speed
of the press. The pressure on both sides of the No. 16A fixed orifice is
sensed on opposite sides of the reducing valve spool. The valve will
maintain a constant pressure drop across the No. 16A fixed orifice.
Flow through the fixed orifice will be the same regardless of the
pressure exerted by the weight of the press. As the platens drop off
when the press opens, the pressure exerted by the weight of the
press will change. The valve spool will shift in response to the
pressure changes maintaining a constant flow through No. 16A.

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10 Relief Valve
When in the Decompression Mode, this relief valve setting
determines the pressure to the rod side of the prefill valve actuator.
1000 PSI is the recommended setting. When the No. 4 “B” solenoid
energizes to start Decompression, the actuator will not immediately
retract because of the pressure on the full piston side of the cylinder.
The pressure on the full piston side will gradually bleed down through
the Nos. 3D, 3C and 4 valves. When the hydraulic force on the rod
side of the actuator is greater than on the full piston side, the actuator
will retract. The relief valve must shift closed in order to retract the
actuator.

11 Check Valve
When in the decompression mode, the oil in the rams bleeds down
through the No. 24 needle valve then through this check valve and
back to tank through the No. 4 directional valve spool. This check
valve allows free flow in one direction, but blocks the oil flow in the
opposite direction.

11A Check Valve

In the compression modes of operation, this check valve will open
and hydraulically connect the main rams with the jack rams.

12B Check Valve

This valve permits free flow from the pumps to the jack rams when
closing the press. The valve will block the oil in the reverse direction
when the press is opening, which forces the oil through the Nos.
9,11,17 & 24 valves.

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14 Filter
This element filters the No. 2B pump volume prior to entering the No.
26 heat exchanger and the No. 2 pump suction port. When operating
at high pressure, normal pump wear can generate enough
contamination to damage downstream components. This filter
should be checked and changed on a scheduled basis. If not already
in place, such a filter schedule can be determined based on the
results of regular oil sampling and analysis. Although not shown on
the schematic, some pressure filters have an internal check valve to
allow the oil to bypass when the element becomes contaminated.

FM, 14 & 26

16A Fixed Orifice

The orifice size of this valve determines the lowering speed of the
press. The oil in the jack rams will flow through this valve before
returning to the tank through the No. 4 directional valve. If this valve
were to become contaminated then the press would open at a slower
speed.

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16B Hand Valve

This valve may be opened when necessary to provide a faster
decompression rate. The valve is closed during normal operation.

18A Manual Valve

This valve is kept closed during normal operation. It is opened
whenever it is necessary to manually drain oil from the main rams,
such as to bleed air from them.

18B Manual Valve

This valve is kept closed during normal operation. It is opened
whenever it is necessary to manually drain oil from the jack rams,
such as to bleed air from them.

18A, 18B & 25

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18C Manual Valve

This valve is kept closed during normal operation. It is opened to
drain oil from the rams whenever it is necessary to manually lower the
press.

18C Manual Valve

19 Manual Valve
This valve should be kept closed during normal operation and
opened whenever necessary to read the gauge. This protects the
gauge from shock in the system.

20B Hand Valve

This hand valve is used when necessary to drain the oil out of the
main rams. A hose or pipe should be connected to this valve and run
into a container or back into the reservoir.

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24 Needle Valve
This valve is used to meter the oil out of the main rams in the
decompression cycle. The setting of this valve controls the rate at
which the rams decompress. If the press takes too long in the
decompression cycle then the valve may be contaminated. By
manually rotating the adjustment counterclockwise 2 – 3 turns, the
flow will many times blow the trash through the valve. Be certain to
reset the valve to its original setting.

25 Sight Glass
When necessary to bleed oil out of the main rams and jack rams, the
manual valves upstream of the sight glass will be open. Oil in the
rams is then ported through this sight glass. The oil color will be a
milky white when air is present. Once the color returns to a light
brown, this means that the air has been bled out of the rams. The
manual valves should be closed after bleeding the air out of the rams.

26 Heat Exchanger
The 2B gear pump volume is ported through this cooler prior to
entering the No. 2 pump suction port. The oil is ported through tubes
inside the shell. The water flow is ported through tubes in the
opposite direction. The heat in the oil is transferred from the oil to the
water. To achieve the most efficient heat transfer, the water flow
should be 25% of the oil flow. The water flow can be controlled by
manual valves, a water modulating valve or an electrical solenoid
valve. Circulating hot wash oil or light distillate through the tube side
or shell side will usually effectively remove sludge or similar soft
deposits. Soft salt deposits may be washed out by circulating hot
fresh water. Some cleaning compounds such as “Oakite” or Dowell”
may be effective in removing more stubborn deposits.

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27 Fixed Orifice
This fixed orifice functions as a pressure snubber for the No. 28
pressure gauge.

28 Pressure Gauge
When the No. 19 hand valve is open, this gauge will indicate the
pressure in the main rams and jack rams while in the compression
modes of operation.

29 Press Recorder
The pressure in the main rams will be indicated on the graph of this
recorder.

30 Pressure Switch
This switch may be used for one of two purposes. The first is to
de-energize the No. 5 directional valve solenoid when the pressure
setting of the switch is reached. This would permit the No. 1 pump
volume to flow back to tank through the No. 5 valve at low pressure.
The switch may also be used to start the high pressure timer once the
pressure setting of the switch is reached.

30 Pressure Switch

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Hot Press No. 3

Hot Press 3 Surge Valve

Press Flow Controls

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 Hot Press No. 3

C Pump Isolation Check Valve

C Pump

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Hot Press No. 3

C Pump Cutaway

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D Pump Remote Compensator Contorl

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D Pump Stroked to “A” Port

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