Theory of Operation
CIRCUIT RELIEF AND ANTICAVITATION VALVE OPERATION
The pilot poppet (F) is pushed off its seat by excess
The main function of a circuit relief valve (M) is to
pressure oil. The oil behind main poppet (C) flow past
protect the components of a work circuit from pressure
the pilot poppet and then through the clearance
spikes when the control valve spools are in neutral.
between the sleeve (E) and cartridge (E) to the return
The circuit relief valve is a pilot-operated poppet type
passage (K). The oil pressure behind the main poppet
relief valve with anticavitation sleeve (D). Circuit relief
is reduced creating a pressure differences across the
and anticavitation valves are used in the bucket, boom,
main poppet because oil flows out faster than oil can
arm, and auxiliary work circuits. The circuit relief valve
flow through the orifice in piston. When the pressure
can be adjusted by the adjusting screw (G).
difference becomes more than the piston spring (J),
the piston (A) moves to the right and the main poppet
At pressures below the circuit relief valve setting the
(C) is pushed open to relieve excess pressure oil to
main poppet (C) remains closed. The oil pressure in
the return passage.
the work port passage (L) is sensed by the pilot
poppet through the orifice (B) in the piston (A). During
When the oil pressure in the work circuit decreases
normal operation, the sleeve (D) for anticavitation
below the pressure setting, the pilot poppet is pushed
valve is held closed because the oil pressure on the
closed by the pilot poppet spring (B) stopping the flow
inner shoulder is greater than the return passage (K)
of oil past the pilot poppet to the return passage. The
oil pressure on the outer shoulder of the sleeve.
oil pressure behind the main poppet increases moving
the piston to the left and pushing main poppet closed.
In relief operation, the oil pressure in the work port
passage (L) exceeds the relief valve pressure setting.
Continued on next page