VELOCITY FUSES
SUB-SECTION 5G
5. Loosen the capscrews which secure the velocity fuses to
3. Carefully loosen the spring stop, and remove the spool
the boom hoist cylinders. Tap the valve to break the oil
from the valve body.
tight seal to allow any trapped pressure to escape. Then
remove each valve and reinstall it on the opposite cylinder
4. Clean the spool and spring cavity with a clean mineral
solvent, Then inspect the valve for wear and replace any
worn parts.
6. Repeat Steps 1 through 3. If oil now flows from the
opposite cylinder, the valve is faulty and must be replaced
Or repaired. However, if oil flows from the same cylinder,
5. Pack the spring with lightweight rustproofing grease,
the cylinder is bypassing oil and must be replaced or re-
and lubricate the spool with clean hydraulic oil. Then in-
stall the spool in the valve body and tighten the spring stop
paired.
securely.
OVERHAUL
6. Check the operation of the valve by first prying the
spool stem out with a screwdriver under the jam nut, and
GENERAL. Repair of this valve should be limited to the
then releasing it. The spool should snap into the valve body
replacement of seals or replacement of the complete valve.
when it is released. If the spool does not snap into the valve
The spool and valve body are selectively fitted and must
body when it is released, binding exists, and the cause of
not be interchanged with other valves or replaced sepa-
the binding must be aIiminated before the machine is re-
rately.
turned to service.
REMOVAL. To remove the valve from the boom hoist
7. When the valve is functioning properly, replace the
cylinder, proceed as follows:
weather cap and jam nuts.
1. Lower the boom onto the boom rest to prevent boom
TROUBLESHOOTlNG
movement while repairing the valve.
The problem usualIy attributed to these valves is erratic
2. Loosen the capscrews which secure the valve to the
downward drifting of the boom when it is resting in an ele-
cylinder. Tap the valve to break the oil tight seal. This will
vated position. This probIem can be caused by two condi-
allow any trapped pressure to escape. Then remove the
tions; namely, by-passing of oil within the valve or by-
valve from the cylinder.
passing of oil within the cylinders. To determine which of
the two causes is responsible for the problem, proceed as
follows:
DISASSEMBLY. To disassemble the valve, proceed as fol-
lows (see Figure 5G-2):
1. Raise the boom several inches off the boom rest, and
extend the boom several feet to appIy a load to the boom
1. Remove the jam nuts and weather cap from the spool
hoist cylinders.
stem.
2. Attach a suitable lifting device to the boom point to
2. Carefully loosen the spring stop, and remove the spool
limit the amount of boom movement while performing the
from the valve body.
test.
3. The remaining parts on the spool may now be removed.
3. Remove the tube connected to the upper (extend) valve
manifold ports. Oil flowing from one port or the other
CLEANING. INSPECTION AND REPAIR. After the valve
indicates that either the velocity fuse or cylinder is by-
has been disassembled, perform the following:
passing oil. To determine which of the components is
bypassing oil, proceed with the remainder of this pro-
1. Discard all O-rings and beck-up rings. Wash all parts in a
cedure.
clean mineral oil solvent and places them on a clean surface
for inspection.
No oil flowing from the manifold ports indicate that the
problem is not caused by the velocity fuses or boom hoist
2. Inspect the mating surfaces of the valve body and valve
cylinders.
manifold for paint, burrs or other damage. Be sure these
surfaces are flat. If they are not, remove slight imperfec-
4. Reconnect the tuba, and lower the boom onto the boom
tions by stoning the surface lightly.
rest. Mark the valve which had oil flowing through it.
5G-2
