The design of totally enclosed mechanical pumps: With particular reference to a 50 H.P. sodium pump

Abstract

An analysis is first made of the influence of design factors on performance of sheathed induction motors, the results being presented in the form of simple general working formulae with the case of the motor for a proposed 50 h.p. Sodium Pump worked out in detail by way of example. The general conclusion is that motors for this duty should have a large ratio of length to diameter, and should work at lower magnetic loading and higher electric loading than is normal practice for unsheathed motors. The maintenance of an adequate reserve of pull out torque constitutes a major design limitation in these circumstances. With the design presented, having a 6-in. diameter motor, 25-in. long, and employing a 0·03-in. thick nlch'rome sheath, 50 h.p. should be obtainable at 1,500 r.p.m. at an overall efficiency of 80 per cent. Increasing sheath thickness to 0·045-in. would drop efficiency by about 3 per cent. Use of a solid rotor, and permitting the liquid metal to penetrate the rotor-sheath gap would involve no serious additional loss. An analysis of the problems of bearing design for use in liquid metals is then made, results being presented in the form of generalized performance charts and a discussion of their implication. The conclusion is that a vertical shaft arrangement with hydrostatic journals and a hydrodynamic thrust bearing offers great advantage. A general arrangement drawing incorporating the previously discussed recommendations in a particular design of a pump is shown.