Contamination Control

1. Contamination Control Lesia Olinek and Joanie Zucal October 31, 2002 MCT 336

2. “over80 percentof hydraulic system failures are due to poor fluid condition” Contaminant: is any material in a hydraulic fluid that has a harmful effect on the fluid’s performance in a system.

3. Sources of Contamination • 4 primary sources for solid contamination: • Contaminated new oil • Built-in contamination • Ingressed contamination • Internally-generated contamination

4. 1. Contaminated New oil • Fluid travels through hoses and pipes and then is stored in drums or a bulk tank. • Contributes metal flakes and rubber particles • Water condenses in the tanks • causing rust particles. • Use of a portable transfer cart fitted with a high efficiency filter should remove contaminants

5. 2. Built-in Contamination • Common contaminants include burrs, chips, flash, dirt, dust, fiber, sand, moisture, pipe sealant, weld splatter, paint and flushing solution. • A system flush is used to flush out contaminants • Effectiveness based on filters, temperature, viscosity, and turbulence • Off-load period of “running-in” is a must

6. Cleanliness of Tubes and other conductors • Pipes, tubing, and metal fittings must be absolutely clean before installed. • Inside edge of tubing and pipe should be deburred • Hoses should be flexed several times • Flange fittings must fit squarely on the mounting faces and be properly secured with bolts • Inspect threaded fittings for slivers

7. 3. Ingressed Contamination • Contamination from the immediate surroundings. • 4 major ways that dirt can enter a system • Reservoir vent ports • Power unit or system access plates • Components left open during maintenance • Cylinder seals

8. 4. Generated Contamination • Generated by the system itself • Every internal moving part within the system can be considered a source of self-generated contamination for the entire system • Prevent contamination generation by starting with a clean and fully flushed system and keep system fluid clean.

9. Contaminant Generating Mechanisms Table 6.1 Fig 6.4 Fig 6.5 Fig 6.6 Fig 6.8

11. Critical Clearances in Components • Divided into two principle zones • Up to 5mm for high pressure components • Up to 20mm for low pressure components • The actual clearance will vary widely depending on the component and its’ operating conditions. Figure 6-11

12. The size of a Micron Size of Human Hair= 74m 15m 5m 2m

13. Damage Caused by Contamination • The majority of contaminant particles are abrasive. • Abrasive wear and surface fatigue accounts for almost 90% of degradation failures. • Failures arising from contamination • Catastrophic Failure • Intermittent Failure • Degradation Failure

14. Damage Caused by Contamination • Pumps • Component parts move relative to one another, separated by a small oil filled clearance. • At lower pressures there is less force available to drive particles into critical clearances. • Increasing the pressure is of major significance in determining the effect of contamination on a pump • Oil film thickness • Must support loads hydrodynamically but also be thin enough to allow adequate filling of the pump without cavitation. • Critical clearances are higher where higher viscosities are found, for this reason maximum which is compatible with the inlet conditions should be chosen. • For example, in a Gear pump, contaminants between the tooth and the housing, of between gear teeth are particularly subject to critical clearance wear problems.

15. Damage Caused by Contamination • Motors • The majority of contamination passing through a pump will also reach the motor, and similar performance degradation will occur. • If the volumetric efficiency of the pump falls to 85% of its original value and the motor falls to 90%, then the overall efficiency of the pump and motor will fall to 76.5% (0.85*.9)

16. Damage caused by contamination • Directional Valves • Forces acting on a solenoid are: flow forces, spring forces, friction forces and inertia forces. • Friction forces are dependent on the system cleanliness. If the system is heavily contaminated, higher forces will be needed to move the spool. • Pressure Controls • Abrasive particles in high velocity streams of oil erode internal surfaces. • This situation is common in relief valves which are subjected to full system pressure • Stability and repeatability of pilot controls are also affected by heavy contamination.

17. Damage Caused by Contamination • Bearings • In both rolling and siding contact bearings, a thin oil film separates the ball from the race or the journal surfaces from the shaft. As long as there is no contact between the moving parts, the life expectancy is almost to infinity. If a small particle of contamination serves as a bridge between the moving and stationary objects it will result in damage.

18. Quantifying Fluid Cleanliness • “Cleanliness” is not a general term but rather a specific quantitative value • ISO4406 defines standard for cleanliness of a hydraulic or lubricating fluid • Cleanliness Code is divided into three ranges correlating to 2mm, 5mm, and 15mm

19. Quantifying Fluid Cleanliness • An automatic particle counter is used to count the number and size of particles per millimeter of fluid

20. In this example the 3 range cleanliness code is 20/14/12 1 2 5 10 15 20 25 30 35 40 45 50 Figure 6-24 in Vickers Book

21. Systemic Approach to Contamination Control • Goal: to clean the fluid to the point that contamination is not a factor in the failure of any component in the system during the desired useful life of the system • Set target • Select and position filters in the system. • Confirm that the target cleanliness level is being maintained

22. How to set a target Cleanliness Level • Use Vickers Recommended Cleanliness Code chart (Fig 6.28) • Determine lowest code required by any component in the system • Pressure rating is max system pressure • For any system pressure that is not 100% petroleum oil, set target one Range code cleaner for each particle size

23. How to set a target Cleanliness Level con. • If any 2 or more of the following describe the system, set the target cleanliness one level lower for each particle size. • Frequent cold starts at less than -18 deg C • Intermittent operation with fluid temperatures over 70 deg C • High vibration or high shock operation • Critical dependence on the system as part of a process operation

24. Analysis of a system Your system includes: a fixed gear pump a directional valve a pressure relief valve set at 2000 psi a cylinder The system runs 100% petroleum oil The system is expected to cold start and a failure could stop all production. The recommended cleanliness is __________

25. www.eaton.com

26. Cleanliness code

27. Locating Contamination Control Devices • There are three areas for locating a filter. • Pressure Line • Return Line • Off-loop or kidney loop type

28. Locating Contamination Control Devices • Pressure line filter: • Can be considered the “gateway” contamination control device for the system, however if it is used by itself it does not protect the pump from any contamination particles returned from the system. • Fixed Volume pump operating over 2250psi • Variable Vol. Pump operating over 1500psi

29. Because the Pressure line filter does not ensure total system cleanliness it needs a return line filter

30. Return line filter: • excellent location for the main system contamination control filter, as long as it sees at least 20% of system volume each minute. If flow is less than 20% a supplementary re-circulating pump and filter should be designed in the system. • Care must be taken to size the line filter for the maximum flow it will experience, if not sized properly the filter could rupture.

31. Off line circulating pump and filter • Used when a pressure compensated system is on standby for long periods of time

32. Strainers are frequently used in the inlet between the reservoir and the pump. • Usually a 100 mesh screen that will trap particles larger than about 150 micrometers

33. Filter Element Initial Efficiency • The international standard for rating the efficiency of a hydraulic or lubrication filter is the Multipass Filter Performance Beta Test

34. Filter Element Initial Efficiency cont. • Filtration Ratio (beta) is the number of particles greater than a given size upstream of the test filter divided by the number of particles of the same size downstream of the test filter

35. Filter Construction • 2 basic classifications: • Absorbent • 2 types • Surface- most commonly used for coarse filtration • Depth- used for finer filtration • Adsorbent (active) • Should be avoided in hydraulic systems since they may remove essential additives

36. Filter Construction cont. • Structure is cylindrical in shape • Media used is pleated to provide a larger surface area for trapping • Most common hydraulic filter elements are made of glass fiber material • High dirt holding capacity in comparison to strainers and paper media per unit volume

37. Conclusion Controlling contamination in any hydraulic system is an on going process that can greatly improve system performance and extend system longevity.

38. References • Vickers Industrial Hydraulics Manual • Vickers “The Systemic Approach to Contamination Control” • www.eaton.com