CHASSIS AR 3290293 - Caterpillar

Upstroke
Illustration 3 g00484624
Swing Piston Pump Control Valve during Upstroke (1) Positive flow control spool (2) Lever (3) Horsepower adjustment screw (4) Positive flow control adjustment (5) Constant horsepower control spool (6) Actuator piston (7) Swing control valve (8) Maximum angle servo (10) Swing piston pump (11) Minimum angle servo (12) High pressure cutoff spool (13) Positive flow control port (14) High pressure cutoff adjustment screw The following two conditions can cause an increase in pump discharge oil flow:
An increase in positive flow control pilot pressure
A decrease in pump discharge pressureIllustration 3shows an increase in pump discharge oil flow. The increase in flow is caused by an increase in the positive flow pressure signal. When the swing pilot control valve is activated, the swing pilot pressurized oil is directed to shift swing control valve (7). The same swing pilot pressurized oil is directed to positive flow control signal port (13) in the swing pump regulator control valve. When the pilot signal pressure (positive control pressure) reaches approximately 860 kPa (125 psi), positive flow control spool (1) moves to the right as a result of positive flow control pressurized oil on the left end of the spool.When positive flow control spool (1) moves to the right, pressurized oil from the swing system in minimum angle servo (11) is opened to the case drain. Oil drains through constant horsepower control spool (5), high pressure cutoff spool (12), and positive flow control spool (1). An orifice is located between the two lands in positive flow control spool (1). The orifice is connected by a center drilled passage to the case drain. The left chamber of positive flow control spool (1) is connected to the center drilled hole through a cross drilled hole. The swing pump pressure pushes maximum angle servo (8) to the left in order to upstroke swing piston pump (10). In this condition, swing piston pump (10) is free to upstroke to maximum flow.Note: Positive flow control spool (1) is fully shifted to the right when the positive flow control signal pressure exceeds approximately 1760 kPa (255 psi).When positive flow control spool (1) is fully shifted to the right, the flow of pump discharge oil is regulated by the spool for the constant horsepower control. As the pump discharge pressure decreases the upward force of the actuator piston (6) on lever (2) decreases. The spring force pushes constant horsepower control spool (5) to the left, rotating lever (2) counterclockwise. When constant horsepower control spool (5) shifts to the left, the oil from minimum angle servo (11) is connected to the case drain. Oil drains around constant horsepower control spool (5) and high pressure cutoff spool (12) and through both the cross drilled holes and the small orifice in positive flow control spool (1). The pressurized oil in the swing system that acts on maximum angle servo (8) forces the piston to the left and upstrokes swing piston pump (10) .When maximum angle servo (8) moves to the left, actuator piston (6)