In your last hydraulic maintenance email,
I explained how to use volumetric efficiency
to correctly determine the condition of
a hydraulic pump.
Today I want to continue on this tack
and talk about testing hydraulic cylinders.
The conventional way of testing the integrity
of the piston seal in a double-acting cylinder
is to pressurize the cylinder at the end of stroke
and measure any leakage past the seal. This is
commonly referred to as "end-of-stroke bypass test"
The major limitation of the end-of-stroke bypass test,
is it generally doesn't reveal ballooning of
the cylinder tube caused by hoop stress as a result
of under designed cylinder wall thickness or reduction
of wall thickness through excessive honing.
The ideal way to test for ballooning of the cylinder tube
is to conduct a piston-seal bypass test mid-stroke.
The major difficulty with doing this is that the force
developed by the cylinder has to be mechanically resisted,
which in the case of large diameter, high-pressure cylinders
is impractical.
However a mid-stroke bypass test can be conducted
hydrostatically using the intensification effect.
The necessary circuit along with a step-by-step
procedure for conducting this test is shown at:
http://www.insidersecretstohydraulics.com/cylinder-testing.html
Yours for better hydraulics knowledge,
Brendan Casey
Author of 'Insider Secrets to Hydraulics'; and
'Preventing Hydraulic Failures'.
http://www.hydraulicsupermarket.com/books.html
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