PISTON AS 2776275 - Caterpillar

Illustration 7 shows the pump regulator in a standby position. The load sensing regulator and the horsepower regulator work together in order to regulate the pump flow.The pump servo pistons are connected to the swashplate. Pump output pressure is directed to the upstroke servo piston at all times. The load sensing regulator directs control pressure to the destroke servo piston in order to move the swashplate to the minimum angle for decreased pump flow.With the joysticks in the NEUTRAL position, the electronic controller sets the power shift pressure to a standby value. The increased power shift pressure works against the horsepower control spring.Note: Throughout the discussion of the pump regulator operation, the power shift pressure remains constant. Changes in the power shift pressure can cause the pump to stroke.When all the hydraulic control valves are in the NEUTRAL position, no load sensing signal pressure is directed to the spring side of the load sensing control. With no signal pressure in the spring chamber of the load sensing control, the pump output pressure moves the load sensing spool against the spring force. The load sensing spool opens a passage for the control pressure to the destroke servo piston. The standby pressure acts on the upstroke piston and control pressure acts on the destroke piston. The larger area of the destroke piston moves the swashplate to the minimum angle position.The force that is exerted by the PS pressure piston on the lever overcomes the force of the actuator piston with the corresponding pivot distance.The following conditions exist when the regulator is in the position that is shown in Illustration 7:Conditions Engine ... Running Implements ... HOLD PD ... 2500 to 3000 kPa (360 to 435 psi) Flow ... Minimum leakage through destroke piston Swashplate ... Minimum angle
Illustration 8 g00813319
The control valve is in HOLD position with no LS signal to the pump regulator. PS pressure is delivered from the PRV according to the mode selection on the electronic control.The pump is delivering flow against the closed control valve. The restriction creates pressure on pump output. The load sensing spool is metered to a middle position that is balanced by the pump output and the LS spring. The passage is open for control pressure to the destroke piston. The LS orifice spool is in the open position by pump output pressure. The horsepower spool is pushed by the PS pressure piston against the horsepower spring.Pump output pressure is applied on the upstroke servo piston and the control pressure is applied on the destroke servo piston.The force of the destroke servo piston holds the swashplate at "Qmin". Flow is at a minimum in order to replace the leakage oil.Main Pump Regulator In Upstroke Position
Illustration 9 g00813339
Illustration 9 shows the pump regulator at the start of upstroke that is caused by a increase in the load sensing pressure.The following conditions cause an increase in flow from the main pump:
An increase in the load sensing signal
An increase in power shift pressure from the proportional reducing valve
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