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TIP OF THE MONTH 17 : Rotary vane pump

How to choose the right oil mist eliminator for your rotary vane pump ?

TIP OF THE MONTH 17 : Rotary vane pump

QUESTION: During initial pump down of my vacuum vessel a lot of oil mist is emanated from the exhaust. A colleague has told me to install an oil mist eliminator. Is this correct? If so, which model should I use?

ANSWER: The oil mist eliminator is mounted at the exhaust of a rotary vane pump and separates oil droplets and vapours emitted at the exhaust of the oil-sealed roughing pumps. The efficiency of the filter is more than 99%. The selection of the appropriate filter depends on the application.

ADDITIONAL INFORMATION: During initial pump down large amounts of gas are transferred through the pump. This gas flow transports oil droplets which are released from the oil film on the vanes. Additional oil vapour always is present in vacuum systems due to the natural vapour pressure of the oil above the liquid phase.

The oil mist eliminator is mounted at the exhaust of a rotary vane pump and separates oil droplets and vapours emitted at the exhaust of the oil-sealed roughing pumps. When the eliminator is mounted vertically above the pump, the condensed oil is recovered by flowing back through the cartridge into the oil casing. This occurs only if the inlet pressure is less than typically 1 mbar.

The filter selection depends on the application. The commercially available filters can be selected according to housing and filter cartridge material. Entry-of-range filters like adixen’s OME 25S are using a polyamide body and glass fibre reinforced epoxy resin cartridge. These filters are well-suited in innocent applications; e.g. when the pump is used for turbo backing in a UHV surface analysis system.

You should not use a standard oil mist eliminator (OME) if you need to pump corrosive or toxic media. For these applications the OME 25C/H is optimum with its stainless steel body and chemically resistant filter cartridge. This filter is used with adixen’s C- or H-series RVPs. If you are using standard series RVPs with lubricants with very heavy molecules (PFPE, A113, ...) the OME 25C/H is the optimum filter as well. In addition to the high resistance against chemical attack high leak tightness is the main criterion of this filter.

Finally there are the OME 25HP and HP+. These filters are distinguished by their cartridge. The “+” version has an even higher capacity. The HP family is designed for cyclic operation and is of optimum use for frequent cycling. The HP versions are the pre-requisite for the use of oil return kits.

Please observe that the filters can be saturated and the cartridges are consumables ! You can recognize saturation by excessive fumes or droplets, or bursts of vapours appear at eliminator outlet. On the HP series oil level appears at the sight glass. The time taken to reach saturation point depends on the number of pumping operations, their frequency, the volume of pumped gas, and the kind of the oil used. If you make any of these observations please take actions to exchange the filter cartridge as soon as possible.

Some filter cartridges are flammable. Do not use oil mist eliminators when pumping flammable gases like oxygen or silane. Avoid filter blocking: if you need to degas resins please consult adixen application support.

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