48 02/02
PROBABLE CAUSES
NOISY PUMP
Air in the system: Check fittings, cracked
hoses and other parts on the pump intake.
Check hydraulic tank. The tank must be kept
3/4 full.
CAUTION: Never fill hydraulic tank
completely full at any time. System
drainage will cause the tank to overfill
and spill out.
Cavitation (vacuum in pump): Check for
clogged or restricted intake line or plugged air
vent in tank.
Loose or worn pump parts: Look for worn
gaskets and replace if necessary. Check for
clean and proper fluid.
Stuck pump vanes, valves, pistons, etc:
Disassemble and clean thoroughly. Avoid the
use of files, emery cloth, steel hammers, etc,
on a machined surface. Products of fluid
deterioration such as gums, sludges, varnishes
and lacquers may cause sticking. Use solvent
to clean parts and dry thoroughly before
reassembling. If parts are stuck by corrosion
or rust, they will probably have to be re-
placed.
Pump out of alignment with drive: Check
alignment. Misalignment may be caused by
temperature variation.
OVERHEATING
Viscosity too high: Check recommendations.
Unusual temperature conditions may cause
fluid of proper viscosity for working tempera-
ture to thicken too much on the way to the
pump. In this case, use of a fluid with higher
viscosity index may cure trouble.
High discharge pressure: Such parts may
cause undue friction. Look for signs of exces-
sive friction. Be sure all parts are in alignment.
Low oil: Assure oil level is proper, at least
3/4 full. If the tank is low, less fluid will be
available to carry away the heat, raising the oil
temperature.
PUMP NOT PUMPING
Pump shaft turning in the wrong direction:
Shut down immediately. Some types of pumps
can turn in one direction only.
Intake clogged: Make sure tank is cleaned
periodically. Fluid must be kept 3/4 full.
Air leak in intake: If any air is going through
pump, it will cause noise. Pour fluid over points
suspected of leakage; if noise stops, you have
found the leak.
Oil too heavy: If fluid is too heavy, some types
of pumps cannot pick up prime. Fluid that is too
heavy can do great damage to hydraulic sys-
tems. Drain and refill with oil of the proper
viscosity.
LOW PRESSURE IN SYSTEM
Relief valve setting too low: With an im-
proper setting, fluid may flow from the pump
through the relief valve and back to the tank
without reaching the point of use. To check
relief setting, block pressure line beyond relief
valve and check line pressure with a pressure
gauge
Relief valve stuck open: Clean dirty relief
valves (see Maintenance). A stuck valve may be
an indication that the system contains dirty or
deteriorated hydraulic oil.
Broken, worn or stuck pump parts: Install
pressure gauge and block system just beyond
relief valve. If no noticeable pressure is devel-
oped and relief is okay, look for mechanical
trouble in pump. Replace worn and broken
parts.
Valves sticking or binding: Check suspected
parts for mechanical problems such as misalign-
ment, bent, worn etc then look for signs of dirt,
sludge, varnishes and lacquers caused by dete-
rioration.
Sluggishness when machine is first started:
Sluggishness is often caused by fluid that is too
thick at starting temperatures. If you can put up
with this for a few minutes, fluid may thin out
enough to give satisfactory operation, but if it
does not thin out or if surrounding temperature
remains relatively low, you may have to switch
to a fluid with a lower pour point and lighter
viscosity. Under severe conditions, immersion
heaters are sometimes used.
SERVICING HYDRAULICS
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