LIFT CYLINDER CIRCUIT
Lift Cylinder Down
When the bowl valve spool in control valve (3) is held in DOWN position (A), the oil from pump (20) in line (16) goes
out of the control valve through line (5) into the head ends of lift cylinders (2). The DOWN position of the valve spool
also opens a passage for the oil in vent line (8) to go through the control valve to the tank. The pump oil in the head
ends of cylinders (2) moves the pistons and rods down, lowering the water distributor. The pistons push the oil from the
rod ends of the cylinders and opens carry check valves (4). The check valves open because the oil in vent line (8) can
go to the tank. The rod end oil, pushed through valves (4), goes through line (9), through control valve (3), through
return oil line (13) into the filter and tank (19).
Relief valve (10) in control valve (3) prevents high oil pressure damage to the parts in the oil circuit of pump (20). If
pump oil pressure increases to approximately 2525 psi (177 kg/cm 2) (17 425 kPa) the pressure opens the relief valve
and the pressure can not increase any farther.
Release the control lever and a spring on the valve spool moves it to HOLD position (B). Now the pump oil goes to
the filter and tank and a passage for the oil in vent line (8) is closed. The stopped oil in vent line (8) keeps the carry
check valves closed. The water distributor can't go down because the pistons in the lift cylinders can't push oil through
the closed carry check valves.
SCHEMATIC OF HYDRAULIC SYSTEM FOR LIFT CYLINDER DOWN
1. Water pump hydrau-
11. Elevator control
16. Filter and tank.
valve (in HOLD
17. Pump (cylinders and
2. Lift cylinder.
Vent line (for carry
3. Cylinders control
12. Return oil line.
18. Pump (elevator).
Oil line (for rod ends
13. Relief valve (water
4. Carry check valve
cylinder oil circuit).
14. Oil line.
5. Oil line (for heads of
10. Oil line (to elevator
15. Oil line (for