Dry Start-ups and Their Consequences

Insider 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 truth.

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.