I was asked recently to give a second opinion on the cause of failure of a hydraulic piston pump. The hydraulic pump had failed after only a short period in service and my client had pursued a warranty claim with the manufacturer.
The manufacturer rejected the warranty claim on the basis that the failure had been caused by contamination of the hydraulic oil. The foundation for this assessment was scoring damage to the valve plate–see exhibit 1.
How does contamination cause this type of damage to a hydraulic pump?
When hydraulic oil is contaminated with hard particles that are the … continue reading »
Hydraulic components are unique in that it is often possible to offset or balance hydrostatic forces to reduce loads on lubricated surfaces.
By reducing surface loading, the maintenance of full-film (hydrodynamic) lubrication is improved and therefore boundary lubrication conditions are less likely to occur.
Hydrostatic force is the product of pressure and area. Expressed mathematically: F = P x a. The balancing or offsetting of hydrostatic force is achieved by exposing opposing areas to the same pressure.
The double-acting cylinder in Figure 1 illustrates this concept. The rod-side area of the piston, area B, is 80% of area A. This … continue reading »
Load-sensing is a term used to describe a type of variable pump control used in open circuits. It is so called because the load-induced pressure downstream of an orifice is sensed and pump flow is adjusted to maintain a constant pressure drop (and therefore flow) across the orifice. The ‘orifice’ is usually a directional control valve with proportional flow characteristics, but a needle valve or even a fixed orifice can be employed, depending on the application.
In hydraulic systems that are subject to wide fluctuations in flow and pressure, load-sensing circuits can save substantial amounts of input power. In systems … continue reading »