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Selasa, 09 November 2010

Air, how to locate abnormal heat load

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Hello again Air,

In your last hydraulic maintenance email,
I outlined a procedure for determining whether
the root cause of an overheating problem lies
in the cooling circuit or elsewhere in the
hydraulic system.

If the indications are that the cooling circuit
is functioning satisfactorily but the system is
overheating - then we need to locate the source
of the 'abnormal' heat load.

When fluid moves from a high pressure zone to a
low pressure zone we call this pressure drop.

When a pressure drop occurs WITHOUT useful work
heat is generated. For example, the pressure drop
across the ports of a properly functioning motor
produces torque at the motor's drive shaft and
ultimately useful work.

On the other hand, the pressure drop across a relief
valve doesn't produce any work, so this energy is
converted to heat - which is an undesirable heat load
on the system.

Because a pressure drop without useful work creates heat,
an infra-red thermometer can often be used as a quick and
effective means of locating abnormal heat load.

For example, if oil is passing over a relief valve, the
localized heat generation means this component will be
hotter than the rest of the system.

Yours for better hydraulics knowledge,

Brendan Casey
Brendan Casey
Author of 'Hydraulics Made Easy'

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