10.3.2 Liquid-ring type air pump
This is essentially a centrifugal displacement pump. A multi-blade impeller revolves within an offset casing which is partially full of water. The rotating impeller throws the liquid outwards, resulting in a solid ring of liquid revolving in the casing at the same speed as the rotor, but following the shape of the casing.
Figure 4.40 shows how this alternately causes the liquid to enter and recede from the interblade spaces on the impeller.
The provision of inlet and outlet ports enables this pump action to be used for eva¬cuation of air from the condenser. The advantages of this type of pump are that it is simple and reliable, with large clearances on rotating parts, and no valves or pistons.