Vehicle Systems
Hydraulic System Operation
33
Relief Valve
Relief Valve
(7) Passage for return oil. (11) Piston. (12) Dump valve.
(13) Spring chamber. (14) Pilot valve.
If the control lever is held in LIFT or TILT position
after the cylinder rod is fully extended or retracted,
the flow of oil from outlet port to the cylinders is
stopped. The oil under pressure must be released.
The pressure oil flows through piston (11) of the
main relief valve. The pressure oil opens pilot valve
(14).
This lets the oil flow go through spring chamber (13)
to passage (7). The oil then returns to tank. When
the pilot valve opened, it caused a decrease in the
pressure in spring chamber (13) that let piston (11)
move against the force of the spring in spring
chamber (13). This stops the flow of oil around the
pilot valve to passage (7) and moves piston (12)
down until a path is open for pump flow to go to the
tank through passage (7). This action will continue
until the control lever is moved to NEUTRAL position.
