be kept in mind that troubleshooting the regulator is
should, but a bad leak causes the regulator to cycle
done only after the obvious steps have been taken, such
rapidly (chatter). This rapid cycling, as indicated on
as checking the system fluid level to check for external
the system pressure gauge, is usually caused by a
fluid loss and opening shutoff valves.
leaking valve. Thus, a leaking check valve gives
normal regulator cutout and faster than normal cut-in
Troubleshooting the pressure regulator is done by
operation.
timing the cycle of operation--from the cut-in position
to the cutout and back to the cut-in position. A standard
The regulator bypass valve may also leak, causing
regulator operating in a normal system completes this
an indication that affects the cycle of the regulator. If
cycle in a certain period of time. This time can be
the bypass leaks, part of the fluid from the pump, which
obtained from the equipment manual or closely
should be going into the system, bypasses and returns
estimated by maintenance personnel.
to the reservoir. This bypass causes the regulator to
take longer than usual to cut out. Once the regulator has
Since you normally use the pressure regulator only
cut out, the bypass opens. Therefore, it does not affect
with a fixed displacement pump, it should take a
the regulator cut-in cycle.
certain definite time to build up system pressure. For
example, suppose a pump has a volume output of 6
You can see that isolation of different subsystems,
gallons per minute, and the system requires 1 gallon of
sections, and components is a vital part of
fluid to become completely filled (pressurized). As the
troubleshooting the hydraulic system or any one of its
system takes only one-sixth of the pump output to build
components.
up pressure, it should require only one-sixth of a
minute (10 seconds) to pressurize the system. This is
MAINTENANCE
true if the system is in good operating condition. But
what if the system contains an internal leak? In the 10
Hydraulic systems maintenance includes
seconds usually required to build up pressure, the
servicing, preoperational inspections, periodic
pump is still delivering 1 gallon, but some of the fluid is
(scheduled) inspections, repair, and testing following
being lost. Thus, at the end of 10 seconds, the system
repair. The key to hydraulic system dependability is the
cannot be pressurized; therefore, the regulator cannot
attention given to the cleanliness of the repair facilities.
be cut out. The cut-in and cutout pressure of the
Externally introduced contaminants are credited for
regulator can be seen on the system pressure gauge.
more component failure than any of the self-induced
Once the regulator is cut out, the system should hold
contaminations during normal operating conditions.
fluid under pressure for a reasonable length of time.
The various repair procedures for the more
However, if the system leaks, pressure drops fast and
common hydraulic system components are discussed
the regulator cuts in faster than normal. These
in the following text.
indications may mean that the regulator is faulty or the
other components in the system are faulty. However, by
Hydraulic Pumps
isolation techniques, such as subsystem operation and
checking shutoff valves, the problem can be located.
All hydraulic pumps have one thing in
common--precision construction. In general,
If the fault is the regulator, it is probably leaking at
damaged or worn pump parts should be replaced, as
the regulator check valve or at the regulator bypass
they do not lend themselves readily to repair. However,
valve. A leaking regulator check valve is one of the
some manufacturers do allow restoration of sealing
most common and easily recognized troubles. Again,
surfaces to their original flat plane if it can be done by
the regulator cycle is affected. With the regulator
lapping (polishing). Also, very minor scratches,
cut-in, the check valve is open, and fluid is flowing into
scoring, and corrosion can be removed with crocus
the system. When the system pressurizes, the check
cloth.
valve closes, and the regulator is cut out. Therefore, a
leaking check valve does not affect the cutout time of
Generally, the maintenance of hydraulic pumps
the regulator, but it does affect the cut-in time.
consists of disassembly, inspection, repair, and
testing. After disassembly, thoroughly clean and
The purpose of the check valve is to trap fluid
critically inspect all parts for nicks, cracks,
under pressure in the system during the regulator
scratches, corrosion, or other damage that might
cutout operation. However, it cannot do this if there is
cause pump malfunction. Inspect all threaded parts
leakage around the seat. Even a slight leak around the
and surfaces for damage. Inspect pistons, piston
valve seat causes the regulator to cut in faster than it
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