26
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September - October 2019
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www
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machinerylubrication.com
Va r i a ble - d i s pl a c e m e nt
pu mps a re u sed i n
hydraulic systems where
the f low requirements
var y. This usually means the
system has several actuators and,
depending on the current cycle of
the machine, the number of actu-
ators moving at a given time will
fl uctuate. e most common type
of variable-displacement pump is the
pressure-compensating pump.
Pressure-compensating
Pumps
Pressure-compensating pumps
are designed to deliver only the
amount of f low required by the
system to maximize effi ciency and
avoid heat generation. e compen-
sator is adjusted to a pressure
somewhat higher than that required
to move the system's heaviest load.
A pressure-compensating pump
will deliver its maximum f low
until the system pressure reaches
the compensator setting. Once the
compensator setting is reached, the
pump will be de-stroked to deliver
only the amount of fl ow that will
maintain the compensator setting
in the line. Whenever more fl ow is
demanded by the system (such as
would occur when an additional
actuator begins to move), the pump
will increase its stroke to meet
the new fl ow demand. Whenever
the system fl ow needs to decrease
(such as when one or more actua-
tors are stopped), the pump stroke
is reduced. When the system is
stopped completely, the pump
stroke is reduced almost to zero. It
will stroke only a very small amount
or whatever is required to maintain
the compensator setting in the line,
overcoming any system bypassing
or leaks. While a pressure-compen-
sating pump is effi cient, the standby
pressure remains high.
Adjusting Pressure-
compensating Pumps
Adjusting a pressure-compen-
sating pump is quite simple. With all
fl ow blocked and the system idle, the
compensator valve is adjusted to the
When and How to Adjust
a Load-sensing
Hydraulic Pump
HYDRAULICS
Jack Weeks
|
GPM Hydraulic Consulting
"The most
common
reason to
adjust a load-
sensing valve
is because
someone
unfamiliar with
the pump has
mistakenly
attempted
to set the
maximum
system
pressure by
adjusting
the load-
sensing valve
instead of the
compensator."
The compensator and load-sensing valves on a
pressure-compensating pump can look almost identical.
Load-sensing Valve
Compensator
