Scroll pumps

Also for these pumps, multistage systems (e.g. Varian TriScroll Pump) are used which allows for final pressure around 10 2torr and pumping speed of about 30m3/h (see Fig. 1.10). The typical application of scroll pumps systems is the backing for turbomolec-ular pumps (see Section 1.6.6). 

Fig. 1.10. Pumping speed vs. pressure for a three-stage scroll pump (Varian TriScroll 600).

There are two main drawbacks in scroll pumps the production of Polytetrafluoroethy-lene (PITT) powder dust due to the friction between the fixed and the moving part moreover, since in the present commercial versions the motor is not in vacuum, the tightness is not the best. 

As in high vacuum generation in macroscopic scale, the micropump is divided into two parts. As a backing pump for the pressure range from a few 102 Pa to atmospheric pressure a micro-sorption pump is under investigation, which relies on surface adsorption effects, as well as a scroll pump, which ranks with its displacement principle among the classic backing pumps. 

Because of the problems that can potentially arise with oil-sealed pumps, there is an increasing trend to use dry pumps in many applications. Various types are available including Roots pumps backed with suitable pumps (see Section 3.2.3), multi-stage Roots pumps, screw-, hook-and-claw- and scroll pumps. Dry piston pumps and diaphragm pumps are also available but their pumping speed range is restricted. The... 

Among the duties of oils in standard mechanical pumps are those of protection. Since scroll pumps do not have oil, they are dependent upon traps and baffles for protection against gaseous and particulate contamination. Although backstreaming of pump oils is not a concern from a scroll pump, the need for traps still remains. Ironically, the demands of maintenance on traps for scroll pumps is greater than for regular pumps due to the total lack of protection the pump has for itself. 

Genevac HT4 Series II 4 sample swings for up to 8 deep-well mtp, 16 mtp or 4 mtp format blocks proprietary Scroll pump is offered, custom rotors possible... 

Fig. 13.3 A prototype scroll pump for a miniature GCMS system fabricated using the LIGA process, (a) 3 mm PMMA mold, (b) schematic of scroU pump, (c) electroformed scroll pump...

The backing pumps serve two purposes (1) to quickly remove atmospheric gases and establish the minimum vacuum required for the operation of high-vacnnm pumps, and (2) to remove the exhaust gases coming from the high-vacnnm pnmps. Rotary-vane and scroll pumps are the common types of backing pnmps. 

The operation of scroll pumps, a new generation of backing pumps, is based on two Archimedian spirals, one fixed while the other moves with a slightly offset rotation. An Archimedian spiral is one where the distance (spacing) between each rotation of the spiral is constant. Similarly to rotary pumps, scroll pumps operate by capturing... 

Positive displacement pumps are best for evacuating from atmospheric pressure to 10 Torr and for supporting (backing) momentum transfer pumps. Those most commonly found on SIMS instruments are Rotary vane or scroll pumps. 

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