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| Illustration 1 | g00694555 |
(1) Port plate. (2) Barrel. (3) Pistons. (4) Swashplate. (5) Housing. (6) Shaft. (7) Link pin. (8) Bearing sleeve. (9) Servo Piston. (10) Control sleeve. (11) Servo control spool. (12) Spring. | |
The axle propel pump is mounted in tandem with the vibratory pump. The charge pressure for the propel system is supplied by the steering pump. When the engine is operating, drive shaft (6) and barrel assembly (2) are rotating. There are seven pistons (3) in the barrel assembly. Port plate (1) and swashplate (4) are fastened to housing (5). The port plate and the swashplate do not rotate. Spring (12) keeps a force on the barrel assembly in order to make a high pressure seal between the barrel assembly and the port plate. When the barrel assembly is rotating, each piston (3) follows the angle of the swashplate. If the swashplate angle is at zero, the pistons do not move in and out of the barrel assembly and there is no oil flow.
The steering pump maintains charge oil in the propel pump in order to keep the barrel assembly full of oil. The charge oil lubricates the pump components. The internal loss of oil due to leakage is replenished by the charge oil. The charge oil is also used in order to release the brakes and the charge oil will provide the shift valve with oil.
The position of the swashplate is controlled by the servo control spool (11) and servo piston (9). Movement of the propel control lever moves the servo control spool. The spool routes charge oil into the servo piston. The servo piston controls the direction and the amount of the swashplate angle.
Oil flows from the propel pump to the propel motor and back to the propel pump by way of the inlet/outlet ports. The position of the swashplate determines the direction of flow as well as the high pressure side of the two loop lines.
High Pressure and Charge Relief valves
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| Illustration 2 | g00694562 |
(1) High pressure relief valves. (2) Bypass valve. (3) Charge relief valve. | |
High Pressure Relief Valve
The propel pump has two high pressure relief valves. The pump has a relief valve for the FORWARD position and one for the REVERSE position.
The high pressure relief valves (1) function in order to protect the circuit from high pressure spikes. The valve also protects against damage to the circuit components. The oil pressure acts against the force of spring in the relief valve. When the circuit pressure reaches the high pressure relief setting, the spindle is lifted off the seat. This movement instantly dumps high pressure oil into the low pressure side of the closed circuit.
The high pressure relief valves have a second function. The valve acts as a makeup valve for the closed circuit. When the pressure in low pressure side of the closed loop gets below the charge pressure, charge oil fills the closed circuit. When the pressure in the low pressure side of the closed circuit increases to charge pressure, the force of the spring closes the makeup check valve.
Bypass Valve
The propel pump has a bypass valve (2). The valve allows the machine to be towed. In order to tow the machine, back off the bypass valve by two or three turns. This action allows the oil to pass from one side of the closed circuit to the other side.
Charge Relief Valve
The propel pumps have a charge relief valve (3). The charge relief valve is located in the pump housing. When the charge relief valve opens, excess oil is directed back to the hydraulic oil tank. The charge relief valve is not adjustable. If the pressure in the system reaches 2825 kPa (410 psi) the charge relief valve will open. The setting for the charge pressure is adjusted at the relief valve that is located in the flushing valve.
Servo Valve (Piston Pump)
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| Illustration 3 | g00690363 |
(1) Lever. (2) Piston. (3) Neutral adjusting screw for the swashplate. (4) Cavity. (5) Cavity. | |
The control valve is controlled manually. The valve controls the flow of charge oil to the servo piston.
The pump swashplate is moved by the servo piston assembly. The servo valve is a double acting piston that is a part of the propel pump. The swashplate is connected to the piston through lever (1) .
When the propel lever is in the NEUTRAL position, the servo valve is spring centered. Charge oil is blocked by the valve spool. Both ends of the servo piston assembly are vented to the hydraulic oil tank. Piston (2) is held in the center position by adjusting screw (3) and a spring. The pump swashplate is held at zero angle and there is no oil flow from the pump.
When the propel lever is in the FORWARD position or in the REVERSE position, the servo valve is shifted. The servo valve controls the direction and the amount of swashplate angle. The manual displacement control spool has a return spring that is located externally on the pump.