The Lubrication of Slippers in Axial Piston Pumps and Motors—the Effect of Tilting Couples

In addition to the load from the fluid pressure acting on the piston, slippers in axial piston pumps and motors must carry couples produced by the centrifugal loads from pump rotation and by the friction acting at the piston/slipper ball joint. These couples have a major influence on slipper performance and largely control the slipper clearance and leakage. Small amounts of surface non-flatness are known to be necessary for slipper lubrication and it is shown that, on this basis, the behaviour of slippers when subject to tilting couples can be satisfactorily predicted. Neither the magnitude nor precise shape of the surface profile appears to be of critical importance provided that the slipper lands have a generally rounded and convex profile. Measured clearances under slippers subject to tilting couples confirm the theoretical predictions.