Alamo MACHETE Product Service Manual page 149

POSSIBLE FAILURE / CAUSE & SOLUTION
Cylinder Excessive Drift:
NOTE:
All Cylinder Hydraulic Systems have some amount of drift or leakage in the system.
All parts have tolerances and all parts Must have clearance in order to function.
Clearance necessary to allow the part to function also results in some internal
leakage. Cylinder Drift can also be refered to as "Leak Down" or "Settling", In most
cases, the cause of Cylinder Drift will be found in the Cylinder, Valve (s) or Lines.
Components have a different leakage rate. Reducing the amount of drift also has its
drawbacks. "Tight" components are very sensitive to contamination, Seizure due to
high operating temperatures, Seizure due to contamination. Valves have a tight
clearance, restrictors have small openings. Leaking External Lines cause Cylinder
Drift but this is the easiest problem to correct as it is the easiest type to find. There
fore most causes listed below will deal with Internal Leakage. See "Cylinder Drift Rate
Chart" in Specification Section of Product Repair Manual to determine if drift rate is
excessive. See Cylinders Leak Section for Cylinder leak Problems.
CAUSE:
Cylinder Pistons Seals Bypassing? Dual Function Cylinders have 2 lines and have
pressure both ends, Single Function Cylinders have 1 line and pressure on one end
and Vent Plug on other, Piston bypass in Single Action Cylinders it will not require this
test, If they leak the Oil will leak out of Vent Plug.
SOLUTION:
Raise load and support it safely. Drain Pressure off Line after Load is supported and
before removing any lines. Drain Pressure can be done with Tractor "Off" and open
valve to lower Load. Remove and solidly plug lines to the Cylinder. Remove Load
Support (Hoist will be reqiured), Document the time it takes for the load to drift down.
(See Cylinder Drift Chart) If the Piston Seal is cause of excessive Drift down this will
tell you. Reseal or Repair Cylinders as required. Note Piston Seal bypass can be
caused by damaged Seals, oversized or worn Cylinder Bores. Some Cylinders don't
function through out the intire length of their stroke, So the oversize wear could only
be in part of the bore, When checking Bore size it is recommended to check entire
length of Bore if the length of stroke is not known.
CAUSE:
Work Port Relief Valves Not Seating Properly?
SOLUTION:
Test Cylinders for Bypassing as above. If OK, Leakage must be occurring in the
Control Valve Spool or Work Port Reliefs (if Equipped). Suspend the Load with
the Cylinders and place Valve Lever in "Hold" (Neutral / Centered) position. Use a
"Stethoscope" Tool (or equivelant), Listen to the Valve Body next to the Work Port that
is suspect. The Oil will be making a shrill whistling sound as it leaks past the Work
Port Poppet. If Leakage is evident, Lower the Load and inspect to Work Port Relief
Valve, replace if needed.
Machete (Service Manual) 04/04
© 2004 Alamo Group Inc.
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