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Troubleshooting
7.3
Hydraulic Motors
Problem
A.
Oil motor stalls at bottom (no
unusual heat problems)
B.
Oil motor stalls at top (no
unusual heat problems)
C.
Low pressure (okay on down
stroke, sluggish on up.stroke —
high heat)
Note:
Engine labors on upstroke, idles
back at stall on the down stroke.
D.
Low pressure (both strokes -
high heat)
Note:
Engine labors at stall on both
strokes.
Cause
1.
Fluid pump piston seat unthreaded
2.
Valve sticking or oil motor trip rod shifter
assembly separated
1.
Valve sticking
2.
Broken spring retainer (valve rod assembly)
3.
Broken spring or valve rod
4.
Air in hydraulic motor
5.
Air in fluid pump
1.
Blown piston seal
2.
Cracked piston
1.
Blown center o-rings on spool valve
2.
Bad hydraulic pump
GB
Solution
1.
If connecting rod is okay, remove cylinder head plug
and pop valve down. Replace plug and start machine.
If machine cycles up and stops at bottom again, then
problem is piston seat on fluid pump. Check piston seat.
Repair or replace as necessary. If piston seat is okay and
problem does not change, check oil motor.
2.
Remove valve and check for scratches and rough
movement when sliding it up and down. Replace valve
and spool in this condition. Check trip rod for possible
separation.and spool in this condition. Check trip rod for
possible separation.
1.
Remove valve and check for scratches and rough
movement when sliding it up and down. Replace valve
and spool in this condition.
2.
Replace valve rod assembly.
3.
Replace valve rod assembly.
4.
Reset valve. Purge Air, generally accomplished by low
pressure cycling of motor/pump assembly for 5–10
minutes. Check for causes of air introduction:
•
Loose fittings in tank.
•
Loose fittings on hydraulic pump.
•
Loose hose connections.
•
Low oil in reservoir.
5.
Stall at top can occur randomly when fluid pump picks
up air. Reset valve. Avoid air in the fluid pump.
1.
Before dismantling oil motor, start machine. With pump
cycling under pressure, touch the hydraulic cylinder and
the head to see if cylinder or head gets hotter. This will
help determine if piston seal is blown or piston nut is
broken. If heat is on the head, check the o-rings on spool
valve.
2.
Dismantle oil motor and check piston seals cylinder bore
and piston nut. Pay special attention to piston nut. It can
be cracked and not show externally.
1.
Before dismantling oil motor, start machine. With pump
cycling under pressure, touch the head to see if the head
becomes hotter. This will help determine if center o-ring
is blown on spool valve. If hot, remove and replace
o-ring.
2.
Replace hydraulic pump.
24
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