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RECENT DEVELOPMENTS IN HIGH-SPEED RECIPROCATING PUMPS
By F. H. Towler, M.I.Mech.E., and J. M. Towler *
The advent of the self-contained hydraulic press, with its many advantages, has necessitated the development of a compact high-speed pump. For most pressing operations a variable-delivery pump is of little advantage, and such pumps, having rotary valves, are only capable of comparatively low pressures. On the other hand a working pressure of 5,000 lb. per sq. in., with its attendant advantage of compactness, is readily obtainable with pumps having positively seating mushroom type valves. Such a pump is described, which the authprs have perfected, and which has a volumetric efficiency of over 97 per cent at 1,500 r.p.m. High volumetric efficiency is essential to obviate noise and vibration at such speeds and to reduce pulsations in the flow to a practically imperceptible amount.
To obtain high volumetric efficiency at high speeds the shape and construction of the suction valves are of paramount importance. Some comparative experimental figures are given for the discharge of valves of various shapes.
Oil is used as the hydraulic medium as it prevents corrosion and ensures that all working parts are copiously lubricated. The pump is immersed in the hydraulic medium and all rotating parts are mounted on ball or roller bearings. The conditions of loading, the effect of deflexion on the journal bearings, and the special design of shaft are fully described. The paper concludes with various illustrations of self-contained hydraulic presses to which this type of pump has been applied.
This paper is concerned primarily with the development of highspeed reciprocating pumps for service with self-contained hydraulic presses,, riveters, testing machines, and a variety of self-contained hydraulic tools. In recent years there has been an increasing tendency to discard the hydraulic accumulator system in favour of the self-contained hydraulic press. This has necessitated the evolution of a compact high-speed pump in place of the conventional three-throw pump running at from 60 to 120 r.p.m., which was much too bulky and expensive to be embodied in a self-contained hydraulic unit. Before proceeding to describe the efforts which have been made to provide such a pump, it may be therefore useful to consider some of the reasons for this change from the accumulator system to the self-contained unit.
* Directors, Messrs. Towler Brothers (Patents) Ltd., and Messrs. Electraulic Presses, Ltd., Rodley. [I.Mech.EJ 1