Fluid contamination- sources, processes and effects on system.

Sources of contamination in the manufacturing process:

Manufacturing contamination can be resulted from :

  • Components ports not plugged
  • Components stored in a bad environment
  • Pumps/motors prefilled with dirty or unfiltered oil
  • Use of floor dry or similar oil absorbents in shop areas
  • Dirty hands, shop rags & lint used during assembly
  • Dirty workbenches
  • Dirty oil in test bench use to performance check components
  • Welding and fabrication contaminate
  • Broken tools during manufacturing
  • Fittings laying around and not cleaned
  • Dirty hoses from the assembly that were not cleaned and capped
  • Assembly in a fabrication environment
  • Dirty manufacturing procedures
  • Dirty cutting fluid
  • Improper flushing techniques
  • Is a high enough velocity used to create flow turbulence when flushing parts?
  • Dirty ports plugs
  • Shop rags used to plug ports
  • Not cleaning around ports before removing plugs for assembly
  • Reservoirs not cleaned properly before assembly
  • Filters on the shelve but not in sealed con

The Process That Causes For Fluid Contamination And System Damage :

  1. Abrasion: Particles already found in the fluid penetrate the gap between two opposite mobile surfaces (opposite teeth of a gear pump or motor), thus abrading their surfaces. The ensuing particles are a source of contamination.
  2. Erosion: Particles already found in the fluid are pushed against a solid part (metal) at a high speed, abrade its surface, and produce more contaminants. As pressure rises, even the smallest particles foster the erosion process.
  3. Adherence: The contact of two metal parts causes adherence because of molecular attraction; for this reason, some particles can stick together or to any surface.
  4. Mechanical stress: Tearing can occur in highly stressed components; the ensuing particles contaminate the fluid.
  5. Corrosion: Water and other chemical substances attack sensitive materials, Rust due to oxidation increases the number of abrasive particles.
  6. Cavitation And Air Inclusion: The presence of gas can cause or promote cavitation phenomena
  7. Microbial Reproduction: The presence of water promotes the large - scale reproduction of the few microorganisms found in the mineral fluid. Fluid properties are thus undermined and highly corrosive phenomena occur.

Contamination Basics

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 lubricants into a very thin film, less than 1 micrometer thick. If the loads become high enough the film will be punctured by the surface roughness of the two moving parts. The results contribute to harmful friction.

Damages to the system:

  • Wearing of Components: The majority of the contaminates passing through the pump will also reach the motor where it will cause similar performance degradation. If for example, due to wear, the volumetric efficiency of the pump falls to 85% of its original value and the volumetric efficiency of the motor falls to 90% of the original, then the overall volumetric efficiency of the pump and motor will drop to 0.85x0.9=76.5% of the original valve.
  • Hydrostatic Transmission: Hydrostatic transmissions most often consist of a servo-controlled pump and a fixed volume motor. Wear to critical surface in any component will degrade the overall performance of the transmission. Failures of the component can spread debris throughout the system causing extensive and expensive secondary damage. High-efficiency filtration is the key factor in achieving long, reliable service from a close loop hydrostatic transmission.
  • Direction Control Valve: In an electrically operated valve, the forces acting on the solenoid are: flow forces, spring forces, friction forces, and inertia forces. Flow, spring, and inertia forces are inherent factors, but friction forces are to a great extent dependent on the cleanliness. If the system is heavily contaminated with particles similar in size to the radial and the diametrical clearances, higher forces will be needed to move the spool. An even worse situation results from silting, where the contaminant is forced into the clearances under pressure, eventually leading to the breakdown of the oil film and spool binding.

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