HYDRAULIC SYSTEM RT540E SERVICE MANUAL
2-40 Published 4-20-2015, Control # 502-01
HOLDING VALVES
Description
A bolt-on manifold style holding valve is installed on the
boom lift cylinder. A cartridge style holding valve is used on
the telescope cylinder installed in the piston side of the
cylinder.
The holding valve provides meter out control, will lock the
cylinder in place, prevent a load from running ahead of the oil
supply, and will relieve excess pressure caused by thermal
expansion.
Maintenance
Removal
1. Unscrew holding valve from its port block or manifold.
Installation
1. Check the inside of the port block or manifold for any
sharp edges or burrs and remove as necessary with
emery cloth.
2. Install new O-rings onto the holding valve.
3. Lubricate the holding valve and O-rings with clean
hydraulic oil.
NOTE: The holding valve should turn by hand until
compression of the O-rings begins.
4. Carefully install the holding valve into the port block or
manifold until fully seated.
5. Test the holding valve and port block or manifold by
operating the lift cylinder and/or the telescope cylinder,
as applicable. Verify lift cylinder and/or telescope
cylinder works without problems; verify there is no
leaking. Make repairs as needed.
DANGER
Boom must be fully lowered and fully retracted before
removing lift cylinder and telescope cylinder holding
valves.
CAUTION
Do not damage the O-rings during installation of the
holding valve. If the holding valve turns freely then gets
hard to turn, then easy to turn, remove the holding valve
and check the O-rings. They have probably been
damaged by a sharp edge on one of the ports.
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