Why Pump Or Motor Case Prefilling Is Essential

barrel_A4VI was asked recently to conduct failure analysis on a hydraulic 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. This was the result of the hydraulic motor being started with insufficient oil 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 installing the component and connecting its hoses.… continue reading »

Hydraulic Pump Becomes ‘Air Bound’

hydraulic power unitSometime ago I was involved – in a supervisory capacity – in the planned change out of components on a hydraulic machine. The design of the machine’s hydraulic power unit was the all-too-common, cheap and nasty, everything mounted on the tank lid variety. You know the ones – electric motor mounted vertically, with pump submerged in the tank. They’re cheap and easy to build, but a real pain in the butt for anyone who has to work on them.

The scope of work included changing out a tandem gear pump submerged in the tank. On this machine, a 15 minute job – AFTER you’ve spent two hours disconnecting everything to enable the tank lid to be lifted.… continue reading »

How To Test Hydraulic Cylinders

Hydraulic excavator boom cylindersIn a previous post, I described the danger associated with the intensification of pressure in a double-acting hydraulic cylinder. In this post, I will explain how to use the intensification effect to test the integrity of the piston seal in a double-acting hydraulic cylinder. But before attempting this test procedure, it is absolutely essential that the danger associated with pressure intensification in a hydraulic cylinder is fully understood. Therefore, read this article FIRST!

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.… continue reading »