In the operation of the one radial type pump, the cylinder body revolves about a fixed axis which forms a cylindrical valve. As the cylindrical body revolves, the working fluid is alter nately admitted from and exhausted into the two ports respec tively. The fluid comes in under no pressure from the port and is driven out under any required pressure from the port along the shaft. In order to obtain any required variation of pressure the frame to which the connecting rod ends are attached is made to pivot about the fixed centre by a rod attached to the upper end of the frame. In the middle position there is obviously no stroke, and when the neutral position is passed the direction of flow is reversed.
Two views of another type of radial stroke pump are shown in fig. 5 (Hele-Shaw Pump), the left-hand view being in half section, the lower portion of which shows if a revolving case called the "floating ring." The sectional portion in the view shows that this floating ring is carried on ball races r and r, their object being to reduce the frictional wear bf the rollers or slippers by allowing the floating ring to rotate freely with the cylinder body, in which the pistons are carried. If the floating ring is moved bodily along guides on the line a-b (shown in the other view) the stroke of the pistons and the fluid pressure can be varied as required, just as in the previous example.
An improvement in the foregoing pump has been devised, the Hele-Shaw Beacham pump, in which a central valve is employed, a radical change being effected by what is known in mechanical science as "inversion." Instead of pistons operating outwardly and
obtaining their stroke from contact with an eccentric enclosing the whole cylinder body, the pistons are operated from a fixed crank, the cylinder body surrounding the crank and the pistons working inwardly. The variable stroke is obtained by altering the throw of the crank, which is otherwise fixed. The crank is in the form of a live ring mounted with roller bearings on a compound eccentric.
The compound eccentric consists of two parts of equal eccen tricity, the stroke-varying mechanism being arranged to effect rotation of these two parts in opposite directions with the result that the resultant eccentricity may be varied at will from zero to maximum in either direction. This gear was fully described in Engineering, Oct. 16, 1925.
Another important feature of the new pump is the fact that instead of the central plane of the valve ports coinciding with the central plane of the revolving cylinder body, it is displaced so that the central planes of the cylinders and that of the valve ports are separated .from each other. Fig. 6 is a diagrammatic figure which will make the explanation clear. One remarkable effect is the improvement in the matter of silence. The opening and closing of the ports causes water-hammer blows due to the high pressure in an incompressible fluid. These blows are no longer transmitted so as to cause sound vibrations in the enclosing cylinder body.