SUB-SECTION 5F
COUNTERBALANCE VALVES
SUBSECTION 5F
COUNTERBALANCE VALVES
TROUBLESHOOTlNG. The problems that can be ex-
COUNTERBALANCE VALVE (36Z683)
perienced with this valve fall mainly into two areas; namely,
DESCRIPTION. The counterbalance valve is installed
the valve will not hold the boom in a raised position or the
between the boom hoist control valve and the velocity fuses
boom will not lower. To determine the cause of valve
on the boom hoist cylinders. The valve is mounted on the
malfunction, proceed as follows:
inner side of the right hand sidestand. just below and for-
ward of the boom pivot point (see Figure 5F-2).
1. The inability of the valve to hold the boom in a raised
position could be caused by contamination or a worn
The purpose of this valve is to prevent cylinder movement
piston and/or seat. Proceed as follows to determine the
until pressure has been developed in the boom hoist circuit.
cause:
The valve operates as follows (see Figure 5F-1):
A. Raise and lower the boom severaltimes to flush any
When the boom hoist lever is in the raise position, oil from
contamination from the valve which could prevent
the control valve is supplied to the counterbalance valve,
the piston and/or check valve from wating properly.
and the pressure in the valve will increase until it is suf-
B. Elevate the boom to approximately 45 degrees and
ficient to unseat the check valve, allowing the oil to flow
return the control lever to the neutral position.
through the value to the blind end of the cylinders.
C. Allow the boom to remain in this position for several
When the control lever is in the neutral position, oil pres-
minutes and note whether or not the boom lowers.
sure an the top of the check valve is insufficient to hold the
check valve open. The check valve will then be seated by the
D. If the boom lowers, clean the entire charge of hy-
spring inside it, blocking the flow of oil from the blind end
draulic oil thoroughly, using a filter buggy, and re-
of the cylinders.
place the return line filters. After the oil has been
cleaned, repeat Steps A through C. If the boom still
lowers, the problem is most likely a worn piston or
When the control lever is in the lower position, oil flows to
check valve, and the valve should be repaired.
the rod end of the cylinders, while the oil from the blind
end of the cylinders is prevented from returning to tank by
2. If the boom cannot be lowered, the problem is due to
the piston. This causes circuit pressure to increase. A tube
the piston not shifting. This can be caused by blockage in
connecting the rod end of the cylinders to the pilot port of
the pilot line or orifice, or excessive leakage past the piston
the counterbalance valve allows this circuit pressure to be
O-ring. Proceed as follows to determine the cause:
sensed by the valve. Pressure at the pilot port will cause oil
to flow through a fixed orifice, which determines the open-
A. Elevate the boom to approximately 45 degrees, and
ing rate of the piston, until sufficient pressure is applied to
return the control valve to neutral.
the end of the piston to unseat it. When the piston is
unseated, oil in the blind end of the cylinders is allowed to
B. Remove the tube connected to the pilot port of the
return to tank. When the control lever is returned to the
valve.
neutral position, the pressure in the rod end of the cylin-
C. If the piston O-ring is worn, seepage will be observed
ders and at the pilot port drops below the pressure required
at the pilot port. If no seepage is observed, remove
to hold the piston open, thereby allowing the springs above
the valve and pilot tube, and check for blockage.
the piston to seat it. As the piston closes, the oil at the end
of the piston is returned to the pilot port via the small
check valve in the cap end of the valve. The small check
REMOVAL. To remove the counterbalance valve, proceed
valve by-passes the fixed orifice, allowing rapid seating of
as follows (see Figure 5F-2):
the piston.
5F-1
