LEVER 4W6640 - Caterpillar

Illustration 1 g03458456
The piston pump (steering and Hoist), which is shown in the illustration, produces minimum system pressure due to minimum load sensing pressure.
(8) Piston pump (Steering and Hoist)
(8A) Pump control valve
(8B) Spring
(8C) Springs
(8D) Outlet port
(8E) Piston
(8F) Swashplate
(8G) Actuator
(8H) Case drain
(8J) Spool
(8K) Spool
(8L) Load sensing port
(8M) Inlet port
(A) Load sensing pressure
(B) System pressure
(C) Low pressure Piston pump (8) is a variable displacement pump. The output of the piston pump is determined by the angle of swashplate (8F). A greater swashplate angle produces a greater output. Pump control valve (8A) receives a load sensing signal which controls the output of the piston pump.The position of spool (8k) can cause the output of the piston pump to change. Load sensing pressure and springs (8B) act on one side of spool (8K). Pump pressure acts on the other side of the spool.When the machine makes a turn, load sensing pressure moves spool (8K) downward. Pressure is relieved from piston (8E) and the piston pump upstrokes until the pressure requirements of the system are satisfied. The swashplate is angled by spring force and the force due to the oil pressure within actuator (8G).When the pressure requirements of the system are reduced, pump pressure moves spool (8K) upward. Pressure is transmitted to piston (8E) and the pump destrokes until the reduced pressure requirements are satisfied.Spool (8J) limits the maximum pressure which is supplied to the system by the piston pump. Excessive pressure moves spool (8J) upward against springs (8C) and excessive pressure is relieved to the tank. Springs (8B) provide the margin pressure for the system.Component Location
Illustration 2 g03458377
The piston pump (Steering and Hoist) is located beneath the cab.
(8) Piston Pump (Steering and Hoist)
(8A) Pump control valve
(8D) Outlet port
(8H) Case drain
(8L) Load sensing port
(8M) Inlet port