938F Wheel Loader, Powered By 3116 Engine(SEBP2338 - 64) - Documentación Page 1 of 25

Cerrar SIS

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Producto: WHEEL LOADER

Modelo: 938F WHEEL LOADER 1KM02390
Configuración: 938F Wheel Loader 1KM00001-02508 (MACHINE) POWERED BY 3116 Engine

Operación de Sistemas
938F WHEEL LOADER, IT38F INTEGRATED TOOLCARRIER STEERING SYS
Número de medio -SENR6708-01 Fecha de publicación -17/04/1995 Fecha de actualización -12/10/2001

Systems Operation

Introduction
Reference: For specifications with illustrations, make reference to SENR6707, 938F Wheel Loader
and IT38F Integrated Toolcarrier Steering System Specifications. If the specifications in SENR6707
are not the same as in the Systems Operation Testing and Adjusting, look at the printing date on the
cover of each book. Use the specifications given in the book with the latest date.

Steering Schematic
(1) Check Valves (six). (2) Supplemental Steering Group. (3) Flow switch. (4) Diverter Valve. (5) Pressure switch. (6)
Metering pump. (7) Steering cylinders. (8) Steering Control Valve. (9) Hydraulic tank. (10) Filter. (11) Steering pump.
(12) Supplemental Steering pump. (13) Selector Valve. (14) Relief Valve. (15) Spool Valve. (16) Crossover Relief
Valve.
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Component Location For 938F

(2) Supplemental steering group. (6) Metering pump. (7) Steering cylinder. (8) Steering control valve. (9, 10) Hydraulic
tank and filters. (11) Steering pump. (12) Supplemental steering pump.

Component Location For IT38F

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(2) Supplemental steering group. (6) Metering pump. (7) Steering cylinder. (8) Steering control valve. (9, 10) Hydraulic
tank and filters. (11) Steering pump. (12) Supplemental steering pump.

The steering system can be divided into two basic parts: the pilot circuit and the high pressure
circuit. When the machine is equipped with optional supplemental steering, the steering system
includes one additional circuit.

Pilot Circuit
The pilot system controls the movement of spool valve (15) in steering control valve (8). The
components of the pilot system are the steering pump (11), metering pump (6) and hydraulic tank
(9).

Pump oil from steering pump (11) flows to steering control valve (8), branches off and passes on to
metering pump (6).

The metering pump is a small hydraulic hand pump that is used as a metering and directional valve.
The metering pump sends pilot oil through one side of the selector valve when the steering wheel is
turned.

(9) Hydraulic Tank Location.

Located behind operators compartment.

(10) Filter
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(8) Steering Control Valve Location (behind and above plate)

Hydraulic tank (9) is located directly behind the operators cab. Hydraulic filters (10) are located in
the top of the hydraulic tank.

Steering control valve (8) is located in the middle of the right side of the machine. Steering pump
(11) is located behind the operators compartment.

Metering Pump Location

(6) Metering Pump.

Metering pump (6) is mounted on the bottom of the steering column and located under the floor of
the operators compartment.

High Pressure Circuit

Hydraulic Pump Group

(A) Steering Pump Section

The high pressure components are: primary steering pump (11), steering control valve (8), left and
right steering cylinders (7) and hydraulic tank (9) with filters (10).

The steering pump is a variable flow piston type pump which provides pressure oil for both the pilot
circuit and the high pressure circuit.
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(7) Steering Cylinder (right cylinder shown)

The oil for the steering system is sent from hydraulic pump (11) to steering control valve (8). If the
pilot oil, from the metering pump, has moved spool valve (15) to either the right or left turn position,
oil from the pump will flow to the steering cylinders. The pressure of this oil moves steering
cylinder rods and causes the machine to turn.

Supplemental Steering
Supplemental steering pump (12) is mounted onto the front of the transmission, above the output
shaft. Supplemental steering valve group (2) is mounted directly above steering pump (11).

In the event of primary steering pump failure, or the engine stops, diverter valve (4) will allow
pressure oil from supplemental pump (12) to flow to steering control valve (8).

Alert Indicators
(17) Primary steering alert indicator. (18) Supplemental steering alert indicator.

With no oil flow from primary steering pump (11), pressure switch (5) will activate and light an alert
indicator light on the panel in the operators compartment and sound an action alarm.

Steering Pump
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Variable Displacement Piston Pump (Maximum Swashplate Angle Shown)

(1) Swashplate. (2) Port Plate. (3) Compensator Valve. (4) Drive Shaft. (5) Shoeplate. (6) Piston shoe. (7) Piston. (8)
Cylinder barrel. (9) Plug. (10) Seat. (11) Seat. (12) Chamber for load pressure. (13) Pressure compensator spool. (14)
Drain passage to pump case. (15) Flow compensator spool. (16) Passage to swashplate control piston. (17) Passage from
pump outlet. (18) Signal passage. (19) Actuator piston. (20) Spring.

The angle of the swashplate determines how much oil is drawn into each piston bore. The angle
therefore determines how much oil is pushed or pumped out of each piston bore per drive shaft
revolution.

There are infinite swashplate angle positions between neutral (zero degrees or straight up and down)
and the maximum angle. The greater the swashplate angle, the greater the amount of oil pulled into
the pump and the greater the amount of oil discharged through port plate (2) to the output port.

When swashplate (1) angle is minimum (0°), pistons (7) do not move in and out of the rotating
cylinder barrel. Therefore, no oil is drawn into the pump and no oil is pushed or pumped out of the
pump. There is zero displacement from the pump. The pump is not generating oil flow.

The pump has a compensator valve (3) that keeps pump pressure and flow at a level needed to fulfill
the system load and flow needs. The compensator valve does this by either sending pump oil to or
draining oil from actuator piston (19).

The actuator piston works with the swashplate control spring (20) to continually adjust the
swashplate angle. Pump outlet pressure is kept about 2100 kPa (305 psi) above work port pressure
needs.

The compensator valve also has a pressure limiting ability that prevents pump and system overloads.
When work port pressure rises above 22 800 kPa (3300 psi), pressure compensator spool (13) will
override flow compensator spool (15) and lower pump output. This action starts at about 2100 kPa
(305 psi) below the maximum pressure setting.
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The following schematics show how the pump and its compensator valve act during different
conditions in the hydraulic system.

Upstroking

Pump and Compensator Operation

(1) Pressure compensator spring. (2) Flow compensator spring. (3) Cavity. (4) Signal line. (5) Flow compensator spool.
(6) Actuator piston. (7) Case drain. (8) Bias spring. (9) Swashplate. (10) Passage. (11) Line. (12) Passage. (13) Pressure
compensator spool. (14) Pressure compensator cavity. (15) Plug. (16) Check valve. (17) Passage. (18) Passage. (19)
Passage. (20) Check valve. (21) Signal line from metering pump. (22) Pressure line to metering pump. (A-A) Signal
(high). (B-B) Pressure (low). (C-C) Return oil.

Upstroking is when the pump is increasing displacement (output) in response to increased flow
demand. Due to increased flow demand the signal pressure plus the force of spring (2) in cavity (3)
is greater than pump discharge pressure. When this occurs, spool (5) moves down. This blocks the
flow of supply oil to actuator piston (6).

With flow compensator spool (5) moved downward, oil in the actuator piston passage (17) can drain
to passage (18) past flow compensator spool (5), past pressure compensator spool (13) and out
through passage (19) to case drain (7).

The force of bias spring (8) can now move the swashplate toward maximum angle or upstroke. This
increases pump flow. As flow requirements are satisfied, the pump output pressure increases until
the pressure in passage (12) moves spool (5) up to the metering position.

The inlet check valve (20) prevents steering kickback from external forces. In the metering pump
control section there is another check valve between pump supply and return oil ports. The check
valve provides steering capability when the engine is not running, by allowing oil to recirculate
between the metering pump and the steering cylinder.
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Metering Position

Initially, in the metering position (Figure 1), pump pressure is greater than the combined force of
spring (2) and the signal pressure in cavity (3). Spool (5) moves up.

Pressure is now sent to actuator piston (6). This pressure is greater than the force moving swashplate
(9) toward maximum angle (actuator spring). Swashplate (9) angle decreases. Pump output
decreases.

When pump pressure reduces enough, the combined signal pressure and spring force in cavity (3)
move spool (5) down (Figure 2). The oil pressure behind actuator piston (6) flows back to case drain
per previous discussion.

This light up and down spool movement is called metering. Metering keeps the force on both ends
of spool (5) equal. Spring (2) is equal to 2100 kPa (305 psi). Therefore pump pressure is 2100 kPa
(305 psi) greater than the signal pressure. The difference is called margin pressure.

Destroking
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Pump and Compensator Operation

(1) Pressure compensator spring. (2) Flow compensator spring. (3) Cavity. (4) Signal line. (5) Flow compensator spool.
(6) Actuator piston. (7) Case drain. (8) Bias spring. (9) Swashplate. (10) Passage. (11) Line. (12) Passage. (13) Pressure
compensator spool. (14) Pressure compensator cavity. (15) Plug. (16) Check valve. (17) Passage. (18) Passage. (19)
Passage. (20) Check valve. (21) Signal line from metering pump. (22) Pressure line to metering pump. (A-A) Signal oil
(low). (B-B) Pressure oil (high). (C-C) Return oil.

Destroking is when the pump is decreasing displacement (output) in response to decreasing flow
demand. Due to decreasing flow demand, the signal pressure plus the force of spring (2) in cavity
(3) is less than the pump pressure in passage (12). Spool (5) is pushed up.

Oil behind actuator piston (6) cannot go through passage (18) and (19) to case drain (7). Pump oil
now flows through passage (12), past spool (5) through passage (17) and into actuator piston (6).
Pump pressure behind actuator piston (6) is now greater than the force of actuator spring (8).
Swashplate (9) angle decreases. This decreases pump output and system pressure decreases.

Once the lower flow requirements are met the flow compensator spool (5) moves down to the
metering position. Swashplate (9) will maintain an angle that is sufficient to provide the lower
required flow.

Low Pressure Standby

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Pump and Compensator Operation

(1) Pressure compensator spring. (2) Flow compensator spring. (3) Cavity. (4) Signal line. (5) Flow compensator spool.
(6) Actuator piston. (7) Case drain. (8) Bias spring. (9) Swashplate. (10) Passage. (11) Line. (12) Passage. (13) Pressure
compensator spool. (14) Pressure compensator cavity. (15) Plug. (16) Check valve. (17) Passage. (18) Passage. (19)
Passage. (20) Check valve. (21) Signal line from metering pump. (22) Pressure line to metering pump. (A-A) Pressure.
(B-B) Return.

Low pressure standby is when the engine is running and the steering is not being used. There are no
flow or pressure demands on the pump. Therefore, there is no signal pressure in line (4).

Before the engine is started, bias spring (8) holds swashplate (9) at maximum angle. As the pump
begins to turn, making oil flow, pressure builds in the system because of the closed-center metering
pump.

This pressure in passage (12) is felt at the bottoms of both pressure compensator spool (13) (pressure
limiter) and flow compensator (5) (margin) spools. As this pressure increases, it pushes the flow
compensator (margin) spool up against spring (2).

When system pressure becomes greater than 4300 kPa (624 psi) spool (5) will have moved up far
enough to open up a passage for pressure oil to the back of actuator piston (6).

This causes the actuator piston to move to the right which compresses bias spring (8) and moves the
swashplate toward minimum angle. The actuator piston continues to move to the right until it
uncovers the cross-drilled passage of the actuator piston rod, allowing oil to drain to case.

The cross-drilled hole limits the maximum travel of the piston to the right. At this point, the pump is
producing enough flow to make up system leakage and leakage to the pump case through the cross-
drilled hole while maintaining system pressure at 4300 kPa (624 psi).

The pump is at low pressure standby. This pressure is different than margin pressure because of
system leakage and the cross-drilled hole in the actuator piston rod.
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The flow compensator (margin) spool, instead of metering oil, must remain open and move up
higher against spring (2) to provide enough flow to the back side of the actuator piston to make up
the leakage through the cross-drilled hole.

NOTE: Low pressure standby will vary in the same pump as system or pump leakage increases. As
leakage increases, the pump will upstroke slightly to compensate for the leakage, and the actuator
piston will cover up more of the cross-drilled hole. As this happens, low pressure standby will drop
toward margin pressure. When leakage hits the point at which the piston covers the cross-drilled
hole completely, because of the increased swashplate angle required, low pressure standby will
equal margin pressure.

High Pressure Stall

Pump and Compensator Operation

(1) Pressure compensator spring. (2) Flow compensator spring. (3) Cavity. (4) Signal line. (5) Flow compensator spool.
(6) Actuator piston. (7) Case drain. (8) Bias spring. (9) Swashplate. (10) Passage. (11) Line. (12) Passage. (13) Pressure
compensator spool. (14) Pressure compensator cavity. (15) Plug. (16) Check valve. (17) Passage. (18) Passage. (19)
Passage. (20) Check valve. (21) Signal line from metering pump. (22) Pressure line to metering pump. (A-A) Signal. (B-
B) Pressure oil. (C-C) Return oil.

When the hydraulic system stalls under load or when the cylinders reach the end of the stroke, the
system pressure increases. The signal pressure in line (4) and cavity (3) becomes equal to the pump
output pressure. Spring (2) keeps spool (5) shifted down.

When system pressure reaches 22 800 kPa (3300 psi) in passage (12), the upward force on pressure
compensator spool (13) will compress spring (1), and move pressure compensator spool (13)
upward. Supply oil flows through passage (18) and (17) to actuator piston (6).

Pressure felt on the actuator piston will destroke the pump. Pump output (flow) decreases while
system pressure is limited to 22 800 kPa (3300 psi).
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Check valve (16) prevents damage to the pump during stall conditions. Check valve (16) allows
system pressure oil to bypass the margin spool and flow to actuator piston (6).

Metering Pump

Metering Pump
(1) Spool. (2) Sleeve. (3) Outlet to Tank. (4) Load Sensing Line Port. (5) Pump Oil Inlet. (6) Rotor. (7) Rotor Ring. (8)
Drive Shaft. (9) Housing. (10) Right Turn Port. (11) Left Turn Port. (12) Drive Pin. (13) Centering Springs.

Control section (A) consists of a spool (1), sleeve (2) and housing (9). The sleeve is connected to the
spool by drive pin (12), which is installed through a slot in the spool and a hole in the sleeve.
Centering springs (13) are installed through both the spool and the sleeve.

Metering section (B) consists of rotor ring (7) and rotor (6). The spool is connected to the rotor by
drive shaft (8), which has a slot engaged with drive pin (12) and is splined to the metering section
rotor.

The steering column is connected to the spool by a splined coupling. Pump oil flows into the control
section through inlet port (5).
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When the steering wheel is not being turned, most of the flow is blocked by the spool and sleeve,
but a small amount bleeds through a restriction to the hydraulic tank. This ensures a supply of oil at
operating temperature is always available at the metering pump.

When the steering wheel is turned, spool (1) turns a small amount until springs (13) are compressed.
When the drive pin contacts the ends of the spool slots, the sleeve also turns.

As long as the steering wheel is turning, the spool and sleeve turn as a unit and the centering springs
are compressed.

This initial movement of the spool opens passages between the control section and the metering
section. This allows inlet oil flow from port (5) to the metering section.

Metering Section
(6) Rotor. (7) Rotor Ring.

Steering wheel rotation causes rotation of rotor (6) inside rotor ring (7). As the rotor turns a
controlled (metered) flow of pilot oil is sent back through the housing. This oil flows to port (10) or
(11) and then to the steering control valve.

When steering wheel rotation is stopped, springs (13) move the spool and sleeve back into
alignment. This closes the passages between the metering and control sections.

Steering Valve
Neutral Position
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Neutral Position
(1) Right steer pilot port. (2) Pilot spool. (3) Left steer pilot port. (5) Passage. (6) Passage. (7) Passage. (8) Passage. (9)
Metering pump tank port. (10) Crossover relief valve. (11) Make-up valve. (12) Passage. (13) Make-up valve. (14) Tank
port. (15) Centering springs. (16) Pilot chamber. (17) Pilot chamber. (18) Metering orifices. (19) Metering orifices. (20)
Directional spool. (21) Pilot load check valve. (22) Right cylinder steer port. (23) Left steer cylinder port. (24) Metering
pump supply port. (25) Restrictor (metering pump supply). (26) Relief valve. (27) Pump oil inlet. (A-A) Blocked oil. (B-
B) Pump oil.

Directional spool (20) is held in the center position by centering springs (15) and blocks pump oil
from inlet port (27).

Pump stand-by pressure is felt on relief valve (26), and is connected to the metering pump through
restrictor (25) in metering pump supply port (24). A small quantity of oil bleeds to the hydraulic
tank through a restrictor installed in the metering pump.

The steering cylinders are connected to the valve through ports (22) and (23) which are connected to
passages (12) and (6) respectfully.

The steering cylinders are held where they were positioned when steering wheel movement stopped
by oil blocked in passages (12) and (6).

Oil pressure in passages (12) and (6) is felt on crossover relief valve (10). Make-up valves (11) and
(13) are connected to passages (6) and (12) and are normally seated by spring force.

In steering situations, such as when the steering cylinders are moved by shock loading on the
wheels, the pressure generated in the steering cylinders is felt in passage (6) or (12).

If the pressure is above the setting of the crossover relief valve, the valve will open and unload oil
flow to the opposite passage, which is at a lower pressure.

Make up valves (11) and (13) prevent voiding in the cylinder which is opening, allowing oil to be
drawn from tank port (14).
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NOTE: The illustration does not represent a cross section of the valve. Components are shown out
of position for clarity.

Left Turn Position

Left Turn
(1) Right steer pilot port. (2) Pilot spool. (3) Left steer pilot port. (5) Passage. (6) Passage. (7) Passage. (8) Passage. (9)
Metering pump tank port. (10) Crossover relief valve. (11) Make-up valve. (12) Passage. (13) Make-up valve. (14) Tank
port. (15) Centering springs. (16) Pilot chamber. (17) Pilot chamber. (18) Metering orifices. (19) Metering orifices. (20)
Directional spool. (21) Pilot load check valve. (22) Right cylinder steer port. (23) Left steer cylinder port. (24) Metering
pump supply port. (25) Restrictor (metering pump supply). (26) Relief valve. (27) Pump oil inlet. (A-A) Pump oil. (B-B)
Pilot oil. (C-C) Return.

When the steering wheel is turned counterclockwise to make a left turn, pilot oil from the metering
pump enters the valve through pilot port (3).

Pilot spool (2) is offset to the left and oil flows through passage (4) to chamber (17).

Directional spool (20) is offset to the left against the force of spring (15) and metering orifices (19)
are brought into line with passage (5), allowing the pilot pressure to open pilot load check valve
(21).

Oil displaced from chamber (16) by the movement of the directional spool passes through passages
(7) and (5) to chamber (17).

As the directional spool moves to the left, pump passage (27) is connected to cylinder port (23) and
pump oil passes into the head end of the right steering cylinder and the rod end of the left steering
cylinder.

Oil from the rod end of the right cylinder and from the head end of the left cylinder flows into the
valve through cylinder port (22) and to the hydraulic tank through port (17).
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Steering cylinder pressure is now transmitted through the open pilot load check valve (21) to
chamber (17) and through passages (4) and (3) to the metering pump load sensing port.

The metering pump load sensing port is connected to the control section of the primary pump, which
adjusts output to the required level.

How far the directional spool is offset, and therefore the speed at which the machine turns depends
on how fast the steering wheel is turned and the speed of the engine.

Restrictor (25) regulates the oil supply to the metering pump and controls the maximum speed at
which the steering wheel can be turned.

As the maximum speed is reached, pilot oil pressure between the metering pump and the directional
spool will decrease, and the pump output will decrease slightly as the sensing line signal pressure
decreases. This results in a heavier feel at the steering wheel which slows steering wheel rotation.

When steering wheel rotation is stopped, the metering pump is spring centered and the pilot oil flow
to the steering directional valve is cut off.

Steering cylinder pressure closes pilot load check valve (21) and centering spring (15) moves the
directional spool to the center position.

Pilot oil in chamber (17) is displaced through orifices (19) and pilot passages (5) and (7) to chamber
(16).

Right Turn Position

The operation of the system when the machine is steered to the right is similar to the description for
steering to the left.

Component Locations
(1) Right steer pilot. (3) Left steer pilot. (9) Metering pump tank port. (10) Crossover relief valve. (11) Make up check
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valve. (14) Tank return port. (21) Pilot load check valve. (22) Right steer cylinder port. (23) Left steer cylinder port. (24)
Metering pump supply port. (25) Metering pump restrictor. (26) Pressure relief valve. (27) Pump oil inlet port.

Crossover Relief Valve

Steering Control Valve Schematic

(15) Crossover relief valve.

The crossover relief valve is installed in the steering control valve.

The valve relieves shock loading in the steering system and operates when the system is in neutral,
or when the system is articulating the machine.
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Crossover Relief Valve

(1) Screw. (2) Jam nut. (3) Spring. (4) Spring chamber. (5) Sleeve. (6) Holes. (7) Valve face. (8) Passage. (9) Valve
poppet. (10) Drain hole. (11) Sleeve face. (12) Passage. (13) Valve face. (14) Valve seat.

Steering cylinder pressures are felt in passages (8) and (12) of the steering control valve, and on
faces (7) and (13) of valve poppet (9).

The pressure in either of the passages can rise suddenly when the steering cylinders are moved by
external steering forces applied to the wheels.

A pressure rise in passage (8) would act on face (7) of the valve poppet. If the pressure is above the
valve setting, the poppet will move left against the force of spring (3) and the pressure would be
relieved to passage (12) through holes (6).

A pressure rise in passage (12), above the setting of the valve, would act on face (13) of the poppet,
and on face (11) of sleeve (5).

The sleeve and poppet would be offset to the left against the spring, and pressure in passage (12)
would be relieved to passage (8) through holes (6).

Spring chamber (4) is connected to the tank through drain hole (10).

The pressure setting of the valve can be adjusted by means of screw (1) and jam nut (2).

Pressure Relief Valve

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Steering Control Valve Schematic

(13) Pressure relief valve

Pressure relief valve (13) is installed in the steering control valve.

The valve connects the steering control valve inlet passage to the hydraulic tank if the pump load
control fails to regulate the pump output quickly enough when the pressure rises suddenly due to
steering resistance.
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Relief Valve
(1) Screw. (2) Jam nut. (3) Spring chamber. (4) Spring. (5) Tank outlet hole. (6) Outlet hole. (7) Pump inlet hole. (8)
Valve seat. (9) Valve poppet. (10) Drain hole. (11) Drain hole. (12) Annular (having rings) face.

Spring (4) holds valve poppet (9) against seat (8).

Pump pressure is felt in the relief valve through holes (7). This pressure acts on annular face (12).

If the pressure acting on annular face (12) exceeds the valve pressure setting, the poppet is offset to
the left against the force effect of spring (4).

Pressure is then relieved to the hydraulic tank through holes (5) and (6).

Holes (10) and (11) connect the spring chamber to the hydraulic tank.

The pressure setting of the valve can be adjusted by means of screw (1) and jam nut (2).

Supplemental Steering System (Attachment)

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Supplemental Steering Schematic

(1) Check valves (four). (2) Supplemental steering pump. (3) Flow switch. (4) Diverter valve. (5) Check valve. (6)
Pressure switch. (7) Line to steering control valve. (8) Check valve. (9) Hydraulic tank. (10) Filter. (11) Steering pump.

The supplemental steering system has two functions:

1. To supply oil to the steering system if the engine stops when the machine is moving.
2. To add oil to the primary oil flow of the steering system when engine rpm is low and the
machine is moving.

NOTE: Steering is not possible when the engine stops and the machine is moving, unless the
supplemental steering system attachment is installed.

The supplemental steering components are; check valves (four) (1), supplemental steering pump (2),
flow switch (3), diverter valve (4), check valves (5 and 8) and pressure switch (6).

(2) Supplemental Steering Pump

Supplemental steering pump (2) is a ground driven gear-type pump. It is turned as long as the
machine moves. The pump gets its power from the output transfer gears of the transmission.

When the engine is running, primary steering pump (11) sends oil to the steering control valve
through line (7). This oil is used to operate the steering cylinders.
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As soon as the machine starts to move, oil is also sent from supplemental steering pump (2) to
diverter valve (4).

When the machine moves and the engine rpm and primary pump flow rate is low, oil from the
supplemental steering pump and primary pump is combined (flows together) at the intersection of
check valve (5) and (6). This combined oil flows to the steering control valve.

When the machine moves and the engine rpm and primary pump flow rate is high, the diverter valve
sends the oil from the supplemental pump back to the hydraulic tank.

The oil supply for the steering control valve will then come only from the primary pump. If under
this condition, there is a primary pump failure, the diverter valve will immediately send oil from the
supplemental pump back to the steering control valve.

Component Locations
(2) Supplemental steering pump. (3) Flow switch. (4) Diverter valve. (6) Pressure switch. (9) Hydraulic tank.

Check valves (1), flow switch (3), diverter valve (4), check valves (5 and 8) and pressure switch (6)
are all mounted in a manifold assembly above and slightly behind supplemental steering pump (2).
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Supplemental Steering Manifold

(3) Flow switch. (6) Pressure switch.

Flow switch (3) activates (opens) when the oil flow by it is approximately 11 liter/min (2.9 U.S.
gpm) or greater. The switch deactivates (closes) when the oil flow by it is approximately 5.0
liter/min (1.3 U.S. gpm).

When the flow switch deactivates (closes), the supplemental steering action and alert indicator light,
in the operators compartment, will illuminate.

Pressure switch (6) deactivates when primary pump pressure drops below 700 kPa (100 psi). The
switch activates when the primary pump pressure rises above 1200 kPa (175 psi).

When the pressure switch deactivates, the primary steering action and alert indicator light, in the
operators compartment, will illuminate and the action alarm will sound.

Check valves (5) and (8) prevent oil to flow back through the pumps.

The diverter valve is a pilot operated three-way, two position cartridge valve.

When the engine is running, the oil from the primary pump flows to check valve (8). The force of
the oil opens the check valve. The oil then flows past the check valve and through line (7) to the
steering control valve. Check valve (5) will not allow primary oil flow into diverter valve (4).

Diverter Valve

Diverter Valve
(1) Spring. (2) Passage. (3) Outlet port. (4) Spool. (5) Inlet port. (6) Outlet port. (7) Pilot inlet port.
938F Wheel Loader, Powered By 3116 Engine(SEBP2338 - 64) - Documentación Page 24 of 25

When the engine is running, oil from the primary pump flows to the pilot inlet port (7) of the
diverter valve. When the force of the oil on the end of diverter spool (4) is greater than the total
force of the oil and spring (1) on the opposite end of the spool, the diverter spool will move upward
(as shown in the illustration).

When the diverter spool moves upward and the machine is moving, oil from the supplemental pump
flows into passage (5). The oil then flows around spool (4), and out passage (3), and back to the
hydraulic tank. Only the primary pump flow is sent to the steering control valve.

If a primary pump failure occurs, pilot pressure at passage (7) will no longer be present and spring
(1) will force diverter spool (4) to return to its rest position. Supplemental oil flow will now be
directed to the steering control valve through passage (6).

Supplemental Steering Pump

Supplemental Steering Pump Schematic

(1) Check valve. (2) Pump shaft drive gear. (3) Discharge port. (4) Check valve. (5) Check valve. (6) Check valve. (7)
Driven gear. (8) Suction port.

The supplemental steering pump is a gear-type pump that is ground-driven through the transfer
gears. When the machine moves forward or backward oil is sent into the steering system from
discharge port (3).

When pump shaft drive gear (2) turns clockwise, gears (2) and (7) pull oil in suction port (8), past
check valve (5) and around the pump gears. Check valve (1) prevents oil from being pulled in
through discharge port (3). Oil around the gears is sent through check valve (4) and out discharge
port (3). Check valve (6) prevents oil flow back through the pump.

When pump shaft drive gear (2) turns counterclockwise, gears (2) and (7) pull oil in suction port (8),
past check valve (6) and around the gears. Check valve (4) prevents oil from being pulled in through
discharge port (3). Oil around the gears is sent through check valve (1) and out discharge port (3).
Check valve (5) prevents oil flow back through the pump.

Sat Nov 4 04:44:53 UTC-0300 2023

938F Wheel Loader, Powered By 3116 Engine(SEBP2338 - 64) - Documentación Page 25 of 25

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