Vacuum pumps, mechanical Rotary vane

Figure 1.6 depicts the so-called pumping speed diagram of a mechanical rotary vane vacuum pump. The pumping speed is graphed as a function of the intake pressure. 

The most used mechanical vacuum pumps or compressors are reciprocating, liquid-ring, rotary-vane, rotary blower, rotary piston, and diaphragm. 

Fig. 7.14 The proper orientation of a mechanical pump s exhaust condensate trap. Reprinted from N.S. Harris, Practical Aspects of Constructing, Operating and Maintaining Rotary Vane and Diffusion-Pumped Systems, Vacuum, Vol. 31, 1981, p. 176, with kind permission from Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK.

Mechanical pumps are used directly to produce a low and medium vacuum, as well as extensively to back Roots vacuum, turbomolecular and diffusion pumps. These pumps are also called oil-sealed rotary vane pumps as they rely on the use of vanes or blades to compress gases. 

A rotary vacuum pump is essentially a gas compressor. The mechanism of the pump is designed such that it has an eccentric blade or vane rotating to cause four distinctive actions, namely gas introduction, isolation, compression and gas exhaust. The working principle of the mechanism is therefore divided into four steps during the rotation of the vanes, as illustrated in Figure 2. 6 ... 

The mechanical vacuum pump consists of an eccentrically mounted rotor driven inside a cylindrical housing. Two types of mechanical pumps are constructed (a) the rotary piston type, where the rotor comes in close contact with the housing and thus makes the seal between intake and exhaust compartments, and (b) the vane type pump where two vanes, spring-mounted in the rotor, make contact with the walls of the housing and thereby divide the space between the rotor and the housing. Typical construction is shown in Figs. 2 and 3. 

The most effective method of increasing the level of vapour tolerance in an oil-lubricated rotary vane vacuum pump is that of providing a gas ballast, invented by Gaede. In the case of operation with a gas ballast, it is in connection with mechanical vacuum pumps not necessary to aim for a very high temperature level. Even so, an operating temperature level of 60-80 C and a temperature spread which is as uniform as possible should preferably be maintained so as not to provoke condensation at any point. 

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