DIG TRIGGER MODE

Case Drain Filters Check Valve Check Valve Check Valve Check Valve Solenoid Valve Lift Head End Sensor Implement Pump Pressure Sensor

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The implement hydraulic system is built into the loader frame (1). The following components are shown in the loader frame: case drain filters and bypass switches (2), the implement pumps and pump drive (3), the high pressure screen groups and relief valves (5), (6), (7), (9), and the hydraulic tank (4). High pressure screen (7) filters supply oil from the left side fixed

displacement pump. High pressure screen (9) filters supply oil from the right side fixed piston pump. High pressure screen (5) filters supply oil from the variable displacement pump (section of the tandem pump). High pressure screen (6) filters supply oil from the center fixed

displacement pump (section of the tandem pump).

The implement system has two main control valves: the right control valve (8) and the left control valve (10). 2 4 5 6 7 8 9 10 3

The implement hydraulic system is equipped with four case drain filters with bypass switches. These filter groups filter the case drain oil from the four implement pumps. The following filter and bypass switch are in line with the following pump.

Filter (2) and bypass switch (1) are in line with the left side fixed displacement pump. Filter (4) and bypass switch (3) are in line with the center fixed displacement pump. Filter (6) and bypass switch (5) are in line with the variable displacement pump.

Filter (8) and bypass switch (7) are in line with the right side fixed displacement pump. 116 1 2 3 4 5 6 7 8

High pressure screen (2) is a 200 micron filter that is between the implement pump and the relief valve group (3). Each individual implement pump is equipped with it own high pressure screen and relief valve. The relief valve pressure is adjusted by rotating the adjustment screw (1).

Also, the relief valve group (3) is equipped with a check valve (not shown) with free flow out of the valve.

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This illustration shows the front pump drive (2) and implement pumps removed from the loader frame. The right fixed pump (1) and left fixed pump (3) are installed on each side of the

tandem pump (4). The tandem pump is a combination of a fixed piston pump (nearest to the pump drive) and a variable displacement piston pump. The variable displacement piston pump is equipped with a pump control valve (5) that controls the upstroking and de-stroking of the pump when the machine requirements are met.

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1 _{2 3}

4

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The 994F Wheel Loader is now equipped with a new center pump on the front pump drive. The new pump is a two-section piston type pump. The tandem pump is equipped with an impeller pump (charge) that draws oil from the implement hydraulic tank (not shown) and directs oil to the inlet cavities of each pump section.

The pump section that is located next to the front pump drive is a fixed displacement piston pump. This section will continuously supply oil to the main control valve when the engine is running. The displacement for the fixed pump is predetermined by the locking bolts that retain the swashplate at the fixed angle.

The pump section that is away from the front pump drive is a variable displacement piston pump. This section will supply either minimum flow or maximum flow to the main control valve depending on the signal pressure at the pump control valve. The pump control valve will control the output of the variable pump using pump pressure to shift either the remote pressure control spool (not shown) and the pressure compensator spool (not shown). In this illustration showing minimum flow, oil pressure is directed to the large piston and the force against the piston moves the piston rod and the swashplate against the stop. At the same time, the spring and the pressure that is behind the small piston will be overridden. Small piston will allow the swashplate to rotate against the stop. The pump will supply sufficient oil pressure to lubricate the pump and supply instantaneous response to a request for maximum flow.

Piston Pump Inlet

Swashplate Large Actuator Piston Impeller Pump Pump Outlet Pump Outlet Swashplate Lock Stop Lock Stop

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The signal for the control of the upstroke and destroke of the variable displacement piston pump is through a voltage signal from the Implement ECM to the solenoid valve for the

variable displacement piston pump. The solenoid valve opens to relieve or is closed and blocks the oil pressure in the signal line to the pump control valve. In the illustration, the signal oil is relieved to tank pressure.

When the oil at the signal line goes to zero pressure, the oil on the left side of the remote pressure spool is at tank pressure. With the orifice installed in the line between the pump outlet and the solenoid valve, the pressure on the right side of the remote pressure spool is greater than the pressure on the left side of the spool. The spring force on the left side of the remote pressure spool is overridden by the force that is developed by the system pressure on the right side of the spool. The remote pressure spool shifts to the left. System pressure is allowed to flow to the large actuator piston. The pressure in the large actuator piston overcomes the combined force of the small actuator and bias spring and shifts the swashplate to zero angle.

To Hydraulic Tank To Fixed Displacement Pump Small Actuator Piston Large Actuator Piston Variable Displacement Pump Orifice 2 Impeller Pump Bias Spring Pump Output Spring Variable Pump Solenoid Valve Remote Pressure

Control Spool Pump Control Valve

Orifice 1