VALVE SIZING...

Use of Performance Charts

ENGINEERING

FULFLO GUIDED PISTON VALVES valve equal in size to the pipe to which it is connected.
A larger or smaller valve may be used to suit individual
DATA

The trademark FULFLO expresses the basic principle requirements, depending on the permissible amount of
that the relief valve must have flow capacity equal to over-pressure. Assume we have selected a 3/4” valve
that of the pipe lines to which it is connected. The sliding for 17 GPM flow and a cracking pressure of 325 PSI. By
piston concept and internal design contours of FULFLO referring to the pressure range chart, we find that we
valves provide unique flow and stability characteristics may use either a “YS” or a “ZS” spring.
for reliable performance without chatter. Assuming a “YS” spring, draw a line horizontally at 17
FULFLO valves are designed to operate reliably at GPM in the 3/4” valve chart, to intersect the slanted line
pressures as low as 2 PSI and as high as 1000 PSI. The marked “YS” and drop a vertical line to the over-
FULFLO valve reduces velocities through all but the pressure scale to read an over-pressure of 44 PSI. The
controlling interface of the valve thereby minimizing 17 GPM will be discharged at a pressure of 325 + 44 or
system power loss. 369 PSI. The percentage of over-pressure would be
44/325 X 100 or 13.5%.
Unlike ordinary direct acting relief valves, FULFLO
guided piston valves are less responsive to transient If a “ZS” spring is used, extend the horizontal line to the
pressure surges thereby eliminating the tendency to “ZS” slope and the over-pressure is 70 PSU. The
pound, squeal or chatter. Quiet, stable, efficient pressure to pass 17 GPM would be 325 + 70 or 395 PSI
performance is assured in both load regulation and and the over-pressure would be 21.5%. If the over-
system protection applications. pressure is higher than desired for the particular
application, the procedure may be repeated for the next
FULFLO valves operate effectively with all types of larger size valve.
liquids in the full range of viscosities including hydraulic
oils, water, solvents and chemicals. In some cases, maximum flow through a valve at a
given pressure is specified. To determine the cracking
FULFLO valves are not designed to be positive shut off, pressure, assume a 3/4” valve is to pass 12 GPM at 50
and will pass a minimal amount of leakage before the PSI. A horizontal line drawn from the 12 GPM capacity
set pressure. to the intersection with the “WS” spring line results in an
FULFLO valves are NOT designed for use with air, gas over-pressure of 14 PSI, therefore the cracking
or steam. pressure must be 50 – 14 or 36 PSI, and the
Since the FULFLO relief valve is a flow-modulating percentage of over-pressure of only 9 PSI, but the
device, pressure flow characteristics are completely cracking pressure would be 14/36 x 100 or 38.8%. The
different from spring loaded poppet or ball check valves. use of a “US” spring would produce an over pressure of
Both types remain substantially tight up to cracking only 9 PSI but the cracking pressure would then be 50
pressure. When this pressure is exceeded, the – 9 or 41 PSI, which would exceed the rating of the “US”
“conventional” valve pops open with a pressure drop at spring.
very low flow and an exponential pressure rise as the For sizing valves for higher viscosity than 500 SSU, the
flow increases. following formula is used:
In contrast the FULFLO valve causes a pressure rise, 4 V2 x area of valve for 150 SSU
over-pressure, as soon as flow starts; pressure V1
increases almost proportionally with flow. Springs and
areas on FULFLO valves are carefully designed to V1 = 150 SSU
minimize this over-pressure. V2 = higher viscosity
Both pressures are important in sizing a valve. Cracking Assume we have the following application,
pressure must be selected high enough to permit GPM = 10
system operation at its maximum rated pressure and
Viscosity = 12,000 SSU
flow. Over-pressure is limited by the system’s capability
to withstand the additional pressure and the motor’s Normally for 10 GPM a 1/2” valve would be used.
ability to sustain the pump output at the increased Referring to the orifice area chart on page 9, to find the
pressure for the required time interval. area of a 1/2” valve. The area is .305.
The over-pressure to produce a certain flow is a
4 12000 = 4 80=2.99
function of valve size and spring constant and can be 150
determined with the aid of the over-pressure charts 2.99 x .305=.9120 area needed to pass 10 GPM
given for the different valve sizes. The valve
performance charts are based on tests made with oil of Again referring to the orifice area chart, we find that the
150 SSU viscosity at 100˚ F and may be used with area of 11/4” valve is 1.224. Therefore a 11/4” valve
reasonable accuracy within the conventional range of would be used. To find the over-pressure refer to the
oil viscosities from 30 to 500 SSU. For operation with performance chart for a 11/4” valve.
high viscosity fluids, consult FULFLO’s engineering Performance charts based on actual test results are
department. available on request. For additional information contact
In sizing a valve, the first attempt should be to select a THE FULFLO SPECIALTIES CO.

4
 HYDRAULIC BYPASS
RELIEF VALVES
]

To better understand the valve, and how it can be used in applications, please see the
following definitions.

A pressure safety valve actuated by inlet static pressure and

Pressure Safety characterized by rapid opening or rapid popping action. This safety
Valve (PSV) valve is tight shut-off and is for safety only. Meets ASME SEC.
VIII (Not a Fulflo valve)

Pressure Relief Valve A pressure relief device designed to re-close and prevent further
(PRV) flow after normal conditions have been restored. (Fulflo)

A spring loaded pressure relief valve, actuated by the static pressure

Relief Valve (RV) upstream of the valve. The valve opens normally in proportion to
the increase in pressure over the set pressure. (Fulflo)

A pressure relief valve characterized by rapid opening or pop-action

Safety Relief Valve
in direct proportion to the pressure increase, depending on the
(SRV)
application. (Fulflo)

A spring-loaded pressure relief valve whose performance

Conventional Safety
characteristics are directly affected by change in the backpressure of
Relief Valve (CSRV)
the valve. (Fulflo)

The pressure existing at the outlet of a pressure relief valve, due to

Backpressure the pressure in the discharge system. The pressure can be constant
or variable. It is the sum of the superimposed and build-up pressure.

The pressure which the valve starts to leak flow through the valve,
Cracking Pressure
but before the set pressure.

The inlet pressure the valve is adjusted to open, maintain or control

Set Pressure
under service conditions.

Differential Set The pressure differential between the set pressure and constant
Pressure superimposed backpressure.

The static pressure existing at the outlet of the relief device at the
Superimposed time the device is required to operate. It is a result of pressure in the
Backpressure discharge system coming from another source. This pressure may
be constant or variable.

The pressure increase over the maximum allowable working

Accumulation
pressure (M.A.W.P.) of the vessel, during discharge through the
(Overpressure)
pressure relief device.
 Test Procedures with Test Stand
1. Attach valve to the discharge header on a test bench with pump bypass open.

2. Start pumping fluid and gradually close the pump bypass to purge system of air.
When purged, close bypass and begin testing valve.

3. Adjust valve’s adjusting screw (Screw “in” to increase and screw “out” to decrease
the set pressure) until the valve slightly bleeds (begins to spray or mist). The gauge
needle will drop a couple PSI when the valve is at the set pressure. Verify the setting
using a calibrated pressure gauge. [When bypassing flow, the gauge needle will start
to increase, this is accumulation or overpressure]

4. Lock adjusting screw down.

5. Repeat test to verify setting against the pressure gauge and record final test
information on test report.

Valves to be tested on a hydraulic test stand for set pressure. When testing with water
service on “Cast Iron” and “Steel” valves, the valves should be flushed with oil or a rust
inhibitor to prevent the internal bore and piston from rusting. This will cause the valves to
not operate and hang up.

Fulflo valves are not designed to be a positive shut-off valve and will pass a minimal
amount of leakage (about 10-15%) before the set pressure. It is the tight tolerance
between the internal bore (ID) and the diameter of the piston (OD) that will give you the
sealing surface.

Consult factory for further information or visit our web page WWW.FULFLO.COM

Fulflo Specialites, Co
459 E. Fancy Street
Blanchester, Ohio 45107
937-783-2411 Phone
937-783-4983 Fax
 Test Procedures-Inline Testing

1. Start pumping fluid and gradually close the pump bypass to purge system of air.
When purged, close bypass and begin testing valve.

2. Adjust valve’s adjusting screw (Screw “in” to increase and screw “out” to decrease
the set pressure) until the desired pressure setting, the gauge needle will drop a couple
PSI when the valve is at the set pressure. Verify the setting using a calibrated pressure
gauge. Go to step 3 [When bypassing flow, the gauge needle will start to increase,
this is accumulation or overpressure]

3. Lock adjusting screw down.

4. Repeat test to verify setting against the pressure gauge and record final test
information on test report.

Valves to be tested on a hydraulic test stand for set pressure. When testing with water
service on “Cast Iron” and “Steel” valves, the valves should be flushed with oil or a rust
inhibitor to prevent the internal bore and piston from rusting. This will cause the valves to
not operate and hang up.

Fulflo valves are not designed to be a positive shut-off valve and will pass a minimal
amount of leakage (about 10-15%) before the set pressure. It is the tight tolerance
between the internal bore (ID) and the diameter of the piston (OD) that will give you the
sealing surface.

Consult factory for further information or visit our web page WWW.FULFLO.COM

Fulflo Specialites, Co
459 E. Fancy Street
Blanchester, Ohio 45107
937-783-2411 Phone
937-783-4983 Fax