CASE & FRAME GP 3032159 - Caterpillar

Upstroke
Illustration 3 g00622124
Swing Piston Pump Control Valve during Upstroke 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 3 shows an increase in swing pump discharge oil flow due to an increase in the positive flow control pressure signal. When the swing pilot control valve is actuated, the swing pilot pressure oil (positive flow control pressure) shifts the swing control valve. The same swing pilot pressure oil is directed to the positive flow control signal port in the swing pump regulator control valve. When the swing pilot pressure oil (positive flow control pressure) reaches approximately 860 kPa (125 psi), the positive flow control spool moves to the right as a result of positive flow control pressure oil on the left end of the spool.When the positive flow control spool moves to the right, pressurized oil from the swing system in the minimum angle servo is opened to the case drain. Oil drains through the constant horsepower control spool, the high pressure cutoff control spool, and the positive flow control spool. An orifice is located between the two center lands on the positive flow control spool. The orifice is connected by a center drilled passage to the case drain. The left chamber of the positive flow control spool is connected to the center drilled hole through a cross drilled hole. The swing pump discharge pressure oil pushes the maximum angle servo to the left in order to upstroke the swing piston pump. In this condition, the swing piston pump is free to upstroke to maximum flow.Note: The positive flow control spool is fully shifted to the right when the positive flow control signal pressure exceeds approximately 1760 kPa (255 psi).When the maximum angle servo moves to the left, the actuator piston moves along the lower side of the lever. The movement of the actuator piston along the lever changes the mechanical advantage. The swing pump discharge pressure oil pushes the lever clockwise. The lever pushes the constant horsepower control spool back to the right. The center lands of the constant horsepower control spool meters the flow to the minimum angle servo and the flow from the minimum angle servo.As the maximum angle servo moves to the left, the actuator piston housing increases the spring force on the right end of the positive flow control spool. The positive flow control spool shifts to the left which closes the cross drilled hole in the left chamber of the positive flow control spool. The center drilled passage remains open to the case drain through the small orifice that is located between the two lands. The force on the maximum angle servo and the force on the minimum angle servo are balanced and the swashplate stops rotating. The swashplate is balanced at this position until one or more of the separate control pressures change.Destroke
Illustration 4 g00622125
Swing Pump Regulator Control Valve during Destroke The following two conditions cause a decrease