50 02/02
PROBABLE CAUSES
NOISY PUMP
Air in the system: Check fittings, cracked hoses
and other parts on the pump intake. Check hydrau-
lic 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, replace if necessary. Check for clean and
proper fluid.
Stuck pump vanes, valves, pistons, etc.: Disas-
semble 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 thor-
oughly before reassembling. If parts are stuck by
corrosion or rust, they will probably have to be
replaced.
Pump out of alignment with drive: Check align-
ment. Misalignment may be caused by temperature
variation.
OVERHEATING
Viscosity too high: Check recommendations.
Unusual temperature conditions may cause fluid of
proper viscosity for working temperature 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 excessive 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 periodi-
cally. 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 systems. Drain and
refill with oil of the proper viscosity.
LOW PRESSURE IN SYSTEM
Relief valve setting too low: With an improper
setting, fluid may flow from the pump through 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 (see pressure settings).
Relief valve stuck open: Clean dirty relief valves
(see Maintenance). A stuck valve may be an indica-
tion that the system contains dirty or deteriorated
hydraulic oil.
Broken, worn, or stuck pump parts: Install pres-
sure gauge and block system just beyond relief valve.
If no noticeable pressure is developed 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 misalignment, bent
or worn, etc. Then look for signs of dirt, sludge,
varnishes, and lacquers caused by deterioration.
Sluggishness when machine is first started: Slug-
gishness 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,
lighter viscosity. Under severe conditions, immer-
sion heaters are sometimes used.
SERVICING HYDRAULICS
To Next Page
Loading...