Hydraulic fluid decompression and how to control it

photo credit eaton vickersOne of our readers wrote to me recently regarding the following problem:

“I have a problem with a large garbage compactor. Each and every time the valve cycles the hydraulic cylinder, there is a loud bang. What are the possible causes?”

Assuming this noise is being generated by the hydraulics, i.e. it is not a symptom of a mechanical problem, its likely cause is uncontrolled decompression of the hydraulic fluid.

This problem arises because hydraulic fluid is not perfectly rigid. The ratio of a fluid’s decrease in volume as a result of increase in pressure is given by its bulk … continue reading »

A Serious Consequence of Over-pressurizing a Hydraulic System

hydraulic simulation softwareWhen a hydraulic system sees a spike in pressure it won’t necessarily blow up with a bang. But damage can occur in a number of ways. In fact, a single pressure spike of sufficient magnitude can render a hydraulic piston pump or motor unserviceable. Here’s how:

In axial and bent axis piston pump and motor designs, the cylinder barrel is hydrostatically loaded against the valve plate. To maintain full-film lubrication between the rotating cylinder barrel and the stationary valve plate, the hydrostatic force holding them in contact is offset by a hydrostatic force acting to separate the parts. This is … continue reading »

Hydraulic Ram Leak Caused By Operator Error

rod-seal-dieselA client recently asked me to explain a seal failure on a hydraulic ram. The ram had been removed from a hydraulic lift due to a leaking rod seal, but upon inspection, both the rod seal and the surface of the rod were found to be in serviceable condition.

Recall that a hydraulic ram, a.k.a. displacement cylinder, is a single-acting hydraulic cylinder in which fluid pressure acts on the cross-section of the rod i.e. it has no piston–see figure 1.

Because inspection of the rod seal (U-cup type) and the rod’s surface didn’t reveal any obvious cause of failure, I … continue reading »