Equipment for Gas Transport

Diaphragm pumps [Fig. 7.12(i)] also produce pulsating flow. They are applied for small flow rates, less than 100 gpm or so, often for metering service. Their utility in such applications overbalances the drawback of their intrinsic low efficiencies, of the order of 20%. 

Peristaltic pumps [Fig. 7.12(h)] move the liquid by squeezing a tube behind it with a rotor. Primarily they are used as metering pumps at low capacities and pressures in corrosive and sanitary services when resistant flexible tubes such as those of teflon can be used, and in laboratories. 

Turbine pumps [Figs. 7.9(f), 7.12(i), and 7.4(a)] also are called regenerative or peripheral. They are primarily for small capacity and high pressure service. In some ranges they are more efficient than centrifugals. Because of their high suction lifts they are suited to handling volatile liquids. They are not suited to viscous liquids or abrasive slurries. 

Fans accept gases at near atmospheric pressure and raise the pressure by approximately 3% (12 in. of water), usually on air for ventilating or circulating purposes. 

Blowers is a term applied to machines that raise the pressure to an intermediate level, usually to less than 40 psig, but more than accomplished by fans. 

Compressors are any machines that raise the pressure above the levels for which fans are used. Thus, in modern terminology they include blowers. 

Jet compressors utilize a high pressure gas to raise other gases at low pressure to some intermediate value by mixing with them. 

Vacuum pumps produce subatmospheric pressures in process equipment. Often they are compressors operating in reverse but other devices also are employed. Operating ranges of some commercial equipment are stated in Table 7.3. 

Efficiencies drop off rapidly at flow rates much different from those at peak efficiency. 

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