Pilot-Operated Check Valves
There are three types of pilot-operated check valves
purpose of the valve is to prevent reverse flow from
utilized on the crane, two being used in the outrigger
the piston side of the outrigger cylinders.
circuit, and one in the superstructure cab steering
Incorporated within the valve cartridge is a thermal
relief valve set to open at 4,000 psi (27,580 kPa).
The valve associated with the superstructure cab
steering circuit is mounted on the center frame rail
A valve is located in each outrigger cylinder port
just to the right of the outrigger check valve. The
block. The check valve provides two functions; the
valve prevents reverse flow from the front steering
first function is a holding valve, the second function
cylinder, thus locking the cylinder when steering the
provides a thermal relief of the stabilizer.
rear axle from the superstructure cab. Incorporated
in the valve are two thermal relief valves to provide
thermal protection for the front steering cylinder. The
thermal relief valves are set to open at 3800 psi
The valve associated with the outrigger circuit is
located on the center frame rail near the swivel. The
Do not damage the O-rings during
installation of the check valve. If the
check valve turns freely then gets hard to
To remove the check valve, unscrew the check
turn, then easy to turn; remove the check
valve from the stabilizer port block, refer to Figure 2-
valve and check the O-rings. They have
probably been damaged by a sharp
edge of a port.
Check the inside of the port block for any
The check valve should turn by hand
sharp edges or burrs and remove as necessary with
until compression of the O-rings begins.
Carefully install the check valve into the port
Install new O-rings onto the check valve, refer
block until fully seated.
Lubricate the check valve and O-rings with
clean hydraulic oil.