Industrial

A hydraulic power unit is an arrangement of components, which is used to control hydraulic energy. Mainly comprised of a motor, pump and reservoir. Hydraulic systems are used in any form of mechanical device to push, pull or lift. The primary components required to achieve this are discussed below.

  • Motor -AC or DC or Internal combustion engine
  • Hydraulic Pump – Common types gear, piston or vane
  • Reservoir – Holding tank for hydraulic media
  • Filtration – Commonly a strainer for pump inlet, pressure filter for pump outlet, and/or return line filter

-Filtration is a critical part of hydraulic power units, _ ensuring wear is minimised and efficiencies are maintained.

-Suction strainers capture the largest of contaminants and ensure they do not enter the pump. Pressure filters are selected when highly filtered oil is required within the hydraulic system. Contamination within the system is filtered out by the return line filter before it enters the hydraulic reservoir.

-Filterability of a hydraulic oil is significantly influenced by the additives used in the formulation and by the overall hydrolytic stability of the oil

Control Valves – There are many different types of control valves used in many different ways. Pressure control valves limit or control the hydraulic pressure within the hydraulic system. Directional control valves direct the flow of oil around the system and are controlled manually, electrically, hydraulically or pneumatically. These valves are used in separately or combination to gain the desired function of actuators, motors and other components.

Contamination Cause & Effect:

Sources of Contamination

The experience of designers and users of hydraulic and lube oil systems have verified that over 85% of all system failures are a direct result of contamination!

Contaminant particles larger than 25 micron can jam pumps, valves and hydraulic motors. Smaller abrasive particles measuring between 0.5 and 5 micron known as silt which are about the same size as the operating clearances can cause wear, increase leakage, reducing, efficiency and increased temperature.

Contamination & Source:

Particulate contamination is generally classified as ”silt” or ”chip”. Silt can be defined as the accumulation of particles less than 5µm over time. This type of contamination also causes system component failure over time. Chips on the other hand, are particles 5µm+ and can cause immediate catastrophic failure. Both silt and chips can be further classified as:

Hard Particles

  • Silica
  • Carbon
  • Metal

Soft Particles

  • Rubber
  • Fibres
  • Micro organisms

Contaminant Damage

  • Orifice blockage
  • Component wear
  • Formation of rust or other oxidation
  • Chemical compound formation
  • Depletion of additives and oil degradation

Hydraulic fluid is expected to create a lubricating film to keep precision parts separated. Ideally the film is thick enough to completely fill the clearance between moving parts. This condition results in low wear rates. When the wear rate is kept low enough, a component is likely to reach its intended life expectancy, which may be millions of pressurisation cycles.

The actual thickness of a lubricating film depends on fluid viscosity, applied load, and the relative speed of the two surfaces. In many components, mechanical loads are to such an extreme that they squeeze the lubricant into a very thin film, less than l micrometre thick. If loads become high enough, the film will be punctured by the surface roughness of the two moving parts. The result contributes to harmful friction.