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Leak-proof connections for vacuum pumps

12 May 2013

In the creation of a high vacuum, oil-free membrane units act as auxiliary backing or ‘roughing’ pumps, while turbo molecular pumps perform the final compression.

Absolutely fundamental to successful vacuum generation in systems of this kind are reliable and permanently leak-proof connections. We discover how the mid-sized German vacuum generator specialist, Vacuubrand GmbH achieves this across its product range.

For more than half a century, Wertheim, Germany based Vacuubrand GmbH has specialised in vacuum generation technology. The company’s product portfolio spans rotary vane pumps, oil-free membrane pumps to entire vacuum pump stands for use in laboratories, in manufacturing processes or for leak detection, among others. The company’s top priorities are quality and functionality; even after several years of continuous operation, a Vacuubrand pump is expected to function just as reliably and smoothly as it did on the first day.

This is especially the case with Vacuubrand’s membrane pumps, which, due to their oil-free operating principle, smooth running and long life, are popular across a spectrum of applications. Several thousand Vacuubrand MD 1 membrane pumps have been produced since the model was introduced back in 2000. Their primary area of use is to create what the company terms ‘fore-vacuum’ – essentially, the roughing pump pre-stage to turbo molecular pumps.

Turbo molecular pumps need an auxiliary backing or roughing pump, as they cannot compress to atmospheric pressure. Using oil-free diaphragm pumps for fore-vacuum generation in conjunction with turbo pumps decisively improves the cleanliness of the vacuum generation, and often reduces service requirements as well. In many applications, oil-free high vacuum will also be mandated.

Attaining high product quality requires close attention to detail at every level and for Vacuubrand this means finding like minded suppliers. When it comes to the selection of suitable pneumatic connections, Vacuubrand’s preferred supplier is Waiblingen, Germany based Eisele Pneumatics GmbH. Eisele’s components are also included as OEM parts in Vacuubrand’s CAD construction kit, giving design engineers easy access to Eisele components for all of the vacuum specialist’s products.

Eisele offers a very broad product portfolio, so virtually all Vacuubrand’s needs are satisfied from just the one source. Nevertheless, should a customer require something out of the ordinary, parts can be modified to meet specific needs - for example, by turning an additional face or adding a threaded joint. Eisele is certainly no stranger to the production of specially customised components, and currently has around 2,000 of these in its catalogue.

Eisele’s connectors are installed on the outside of the MD 1 and therefore have to perform not only in terms of their leak proofing, but also cope with any adverse environmental conditions. Threaded connections made from anodised aluminium and brass are available for use in non-corrosive vacuum applications and these have served the MD 1 model successfully for many years.

Swivel screw fittings for the MD 1, complete with pre-mounted sealing rings, are delivered by Eisele pre-assembled and ready for mounting. However, where the pumps are to used in corrosive environments, such as may be encountered in chemical analysis, for example, Vacuubrand manufactures its own injection moulded parts from ETFE. Eisele is also prepared to support products like the MD 1, which is likely to remain in use for many years, with a commitment to the long term supply of replacement parts.

Attaining absolute leak free performance
The sealing requirements for vacuum applications are very much more demanding than in normal pneumatic applications, where some leakage - albeit undesirable – is generally tolerated. In vacuum applications, however, even diminishingly small leaks can be detrimental, since the required end vacuum will not reach the level of stability demanded by the application

For this reason, connections and fittings must be fit for purpose. Eisele addresses this by ensuring that all surfaces are extremely smooth and free of burrs, and all sealing surfaces feature a very high degree of plane parallelism, which avoids misalignment during tightening. Eisele’s hose connections are threaded rather than being of the ‘plug-in’ type, which can be accidentally disconnected. A permanent, yet easy-to-install connection system is Vacuubrand’s preferred solution, and Eisele’s components have proved their worth over many years.

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