Dry Start-ups and Their Consequences
Secrets To Hydraulics
I was asked recently to conduct failure analysis on an axial
piston motor that was the subject of a warranty claim. The
motor had failed after only 500 hours in service, some 7,000
hours short of its expected service life.
Inspection revealed that the motor's bearings had failed
through inadequate lubrication, as a result of the motor being
started with insufficient fluid in its case (housing).
A common misconception among maintenance personnel with limited
training in hydraulics, is that because oil circulates through
hydraulic components in operation, no special attention is
required during installation, beyond fitting the component
and connecting its hoses. Nothing could be further from the
After this motor was installed, its case should have been
filled with clean hydraulic fluid prior to start-up. Starting
a piston pump or motor without doing so, is similar to starting
an internal combustion engine with no oil in the crankcase
- premature failure is pretty much guaranteed.
Some of you may be thinking that the case should fill with
fluid through internal leakage. In most cases it will, but
not before the pump or motor has been damaged. In many cases,
this damage may not show itself until the component fails prematurely,
hundreds or even thousands of service hours after the event.
In this particular example the warranty claim was rejected
on the basis of improper commissioning and the customer was
lumbered with an expensive repair bill.
How can this type of failure be prevented?
This example highlights the importance of following proper
commissioning procedures when installing hydraulic components.
As in this example, if the motor case had been filled with
fluid prior to start-up, the failure of this motor and the
significant expense of its repair could have been prevented.