SUB-SECTION 5F
COUNTERBALANCE VALVES
Figure 5F-7. Counterbalance Valve Operation
A. Raise and lower the boom several times to flush any
counterbalance valve. The oil entering the valve is prevented
contamination from the valve which could prevent
from going to the blind end of the cylinder by the check
the piston and/or check valve from seating properly.
valve until sufficient pressure is developed to unseat the
check valve. Unseating the check valve allows the oil to
B. Elevate the boom to approximately 45 degrees and
flow through the valve to the blind end of the cylinder.
return the control lever to the neutral position.
When the control lever is in the neutral position, oil flow is
C. Allow the boom to remain in this position for several
blocked by the control valve, and circuit pressure decreases,
minutes and note whether or not the boom lowers.
allowing the check valve to seat. With the check valve
D. If the boom lowers, clean the entire charge of hy-
seated, the oil in the blind end of the cylinder is prevented
draulic oil thoroughly, using a filter buggy, and re-
from returning to tank by the seated check valve and
place the return line filters. After the oil has been
piston.
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 is sup-
check valve, and the valve should be repaired.
plied to the rod end of the cylinder and the pilot port of
the counterbalance valve. Pressure at the rod end of the
cylinder and the pilot port of the counterbalance valve will
2. If the boom cannot be lowered, the problem is due to
increase until it reaches the setting of the valve, at which
the piston not shifting. This can be caused by blockage in
point the piston will shift, allowing the oil at the blind end
the pilot line or orifice, or excessive leakage past the piston
of the cylinder to return to tank through the counter-
O-ring. Proceed as follows to determine the cause:
balance valve.
A. Elevate the boom to approximately 45 degrees, and
return the control valve to neutral.
T R O U B L E S H O O T I N G . The problems that can be
experienced with this valve fall mainly into two areas;
B. Remove the tube connected to the pilot port of the
namely, the valve will not hold the boom in a raised position
valve.
or the boom will not lower. To determine the cause of valve
C. If the piston O-ring is worn, seepage will be observed
malfunction, proceed as follows:
at the pilot port. If no seepage is observed, remove
1. The inability of the valve to hold the boom in a raised
the valve and pilot tube, and check for blockage.
position could be caused by contamination or a worn
REMOVAL. To remove the counterbalance valve, proceed
piston and/or seat. Proceed as follows to determine the
as follows:
cause:
5F-7
