Diffusion vacuum pump manufacturers    Diffusion pump heaters     Europe, Middle East and Africa     North and South America     Asia Pacific      Germany     Italy     United Kingdom     Edwards vacuum - Manor Royal, Crawley RH10 2LW, United Kingdom E-Mail, Tel. Fax products: Vapour Diffusion Pumps: Rotary vane and dry pumps can produce ultimate pressures of 10-2 to 10-3 mbar, though the ultimate achievable vacuum may be reduced by factors such as big gas loads. Yet many processes, including ones with significant gas loads, require pressures even lower than 10-3 mbar. For such applications, high and ultra-high vacuum devices such as vapour diffusion pumps, turbomolecular pumps or cryopumps are required. Because of the enormous pressure differentials involved, these pumps cannot exhaust directly to atmosphere. Therefore, a backing pump – typically a rotary vane or rotary-booster combination – must be used in conjunction with these pumps. In a diffusion pump, a suitable fluid is vaporised in the boiler of the pump at 200-250oC and the vapour is sprayed into the pump through high velocity jets incorporated in the interior of the pump. Gas entering the inlet of the pump is diffused in the vapour stream and transferred to the outlet of the pump. The vaporised fluid is condensed and returned to the boiler where the cycle is repeated. BOC Edwards has the most comprehensive range of vapour pumps and accessories of any supplier, including a dedicated series for CRT applications other products: Turbomolecular Pumps, Dry vacuum pumps, Vacuum Technology company profile: BOC Edwards is the world leader in vacuum technology for semiconductor, industrial and scientific applications. The company is engaged in the development, manufacture and support of a wide range of vacuum pumps, systems, boosters and accessories based on a number of technologies and capable of achieving high vacuums down to 10-7 mbar. BOC Edwards pioneered the oil-free ‘dry’ pump, originally for the semiconductor industry and now markets a series of dry pumps using claw, roots, scroll and combined mechanisms. Other pumping technologies include rotary vane, vapour diffusion, turbomolecular, cryogenic and sputter-ion.   related pages:   cryopumps,   diffusion pumps,   getter ion pumps,   turbomolecular pumps,   vacuum oil and sealants   Keywords   www.vacuum-guide.com  Diffusion pumps are a type of vacuum pump designed to achieve higher vacuum (lower pressure) than possible by use of mechanical pumps alone. They use a high speed jet of vapor to direct residual gas molecules in the pump throat down into the bottom of the pump and out the exhaust. The high speed jet is generated by boiling the fluid (typically a low vapor pressure oil) and directing the vapor through a multistage jet assembly. Often several jets are used in series to enhance the pumping action. The outside of the diffusion pump is cooled using either air flow or a water line. As the vapor jet impacts the outer cooled shell of the diffusion pump, the working fluid condenses, is recovered, and directed back to the boiler. The pumped gases continue flowing to the base of the pump at increased pressure, flowing out through the diffusion pump outlet, where the pressure is increased to ambient, and exhausted by the secondary mechanical "rough pump". Note that the oil is gaseous when entering the nozzles. Within the nozzles, the flow changes from laminar, to supersonic and molecular. Unlike mechanical pumps, diffusion pumps have no moving parts and as a result are quite durable and reliable. They can function over pressures ranges of 10-8 to 1 pascals. They are driven only by convection and thus have a very low efficiency. Diffusion pumps cannot discharge directly into the atmosphere, so a mechanical forepump is typically used to maintain an outlet pressure around 10 pascals. One major disadvantage of diffusion pumps is the tendency to backstream oil into the vacuum chamber. This oil can contaminate surfaces inside the chamber or upon contact with hot filaments or electrical discharges may result in carbonaceous or siliceous deposits. Due to backstreaming, diffusion pumps are not suitable for use with highly sensitive analytical equipment or other applications which require an extremely clean vacuum environment. Often cold traps and baffles are used to minimize backstreaming, although this results in some loss of pumping ability. more about diffusion pumps (Wikipedia)