Claw pumps

Like Roots pumps, claw pumps belong to the group of dry compressing rotary piston vacuum pumps (or rotary vacuum pumps). These pumps may have several stages their rotors have the shape of claws. 

Due to the work done on compression in the individual pumping stages, multi-stage claw pumps require water cooling for the four stages to remove the compression heat. Whereas the pumping chamber of the pump is free of sealants and lubricants, the gear and the lower pump shaft are lubricated... 

Fig. 2.38 Diagrams illustrating the pumping principle of the ALL ex pump (claw pump without inner compression)...

This pumping speed is achievable using a two-stage oil-sealed rotary pump. If a dry pump, such as a hook-and-claw pump is required, then a Roots + dry pump combination would have to be used because of the limited pult of the dry pump (see Figure 3.3). 

The pumping speed vs pressure curves for hook-and-claw pumps and a multi-stage dry piston pump are shown in Figures 3.3 and 3.4, respectively. 

Figure 3.3 Pumping speed curves for four-stage hook-and-claw pumps (Snom = 100, 50 and 25 m3 /f1) at 50Hz...

Fig. 2.29.1. Working schema of a dry vacuum pump operating on the so-called claw principle. 1 rotors 2, compression chamber 3, suction chamber 4, exhaust slit 5, suction slit 6, purge between stages (Figure from [2.241).

The pumps of the DRYVAC family are the classic dry compressing claw vacuum pumps that are preferably used in the semiconductor industry, whereby the pumps need to meet a variety of special requirements. In semiconductor processes, as in many other vacuum applications, the formation of particles and dusts during the process and/or in the course of compressing the pumped substances to atmospheric pressure within the pump, is unavoidable. In the case of vacuum pumps operating on the claw principle it is possible to convey particles through the pump by means of so called pneumatic conveying". This prevents the deposition of particles and... 

Fig. 2.42. Schematic drawing of the gas path the shortest connection between the claw in a BOC Edwards DrystarGV pump [BOC stages.

Fig. 2.43. Working schematic of a four-stage dry vacuum pump, type BOC Edwards Drystar GV (Figure from [2.25]). Pump sequence inside one claw.

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... 

Dry Vacuum Pumps (DVPs) These use the operating principles of rotary-lobe roots blowers, claw compressors or screw compressors, and hence require electrical power. They run dry and hence at very high temperature due to the heat of compression. Usually,... 

Q. There are other types of vacuum pumps, seldom found in cleaning machines. A fifth type of pump is a dry pump, which can be a screw, scroll (high speed), or claw design. Booster pumps are also dry and a generally rotary lobe type. 

Positive displacement pumps diaphragm vacuum pumps, liquid ring vacuum pumps, rotary vane and rotary piston vacuum pumps as well as Roots vacuum pumps (dry compressing claw and screw pumps are not yet mentioned here but also belong to this group of pumps). 

Claw Vacuum Pump with Inner Compression So-called claw vacuum pumps have been developed both with, and also without inner compression of the taken in vapours, respectively gases. Such pumps with inner compression were and are being manufactured of the three stage type for chemistry applications and attain pressures below 1 mbar absolute. 

Figure 5.15 depicts a sectional view of such a claw vacuum pump with inner compression and has the name EDP 250. 

Figure 5.15 Sectional drawing of the dry claw-type pump EDP 250. (With permission from Edwards Vacuum, Crawley, UK.)...

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