As you’re hopefully well aware, an unrestricted case-drain line is essential on a piston-type hydraulic motor, whether it’s axial, radial or bent-axis design. But when it comes to gear designs: external, internal and gerotor, a case-drain line is generally considered optional. This is because these types of motors don’t have a large-volume case or sump like piston motors do. But they do have internal leakage which by design, usually accumulates in a small cavity just before the shaft seal.

In theory, by installing a high-pressure shaft seal and two check valves as shown in the inset picture, internal leakage is drained into the return line (something that’s not acceptable for a piston motor or pump).… continue reading »

Noise reduction in hydraulic systems often involves isolating the pump/prime-mover assembly using flexible mounts (isolators). In these cases, the use of hose is necessary to maintain the isolation between the pump/prime-mover and the rest of the system.

The flip-side to this though is, although long lengths of hose can reduce structure borne noise, hose is actually an efficient radiator in the frequency range where most of the energy is generated, typically around 600, 900 and 1200 Hertz.

In terms of vibration and noise conductivity, a long length of pipe or tube is the worst configuration. A long length of hose is better than pipe or tube, but still bad.… continue reading »

The objective of flushing a hydraulic system is to eliminate sludge, varnish, debris and contaminated or degraded fluid from conductor walls and other internal surfaces and system dead spots.

Reasons for performing a system flush include:

1. Fluid degradation – resulting in sludge, varnish or microbial deposits.
2. Major failure – combined with filter overload, which disperses debris throughout the hydraulic system.
3. New or overhauled hydraulic equipment – to purge ‘built-in’ debris.

In a perfect world, when a system flush is needed, a power flushing rig would be available to us. Power flushing involves connecting the system to a purpose-built hydraulic power unit to circulate a low viscosity fluid at high velocities to create turbulent flow conditions (Reynolds number > 2000).… continue reading »