Abstract: A piston pump having a piston element slidable in a piston-chamber forming member with an outer end of a hollow stem of the piston element extending outwardly from the piston-chamber forming member. By relative reciprocal sliding of the piston element relative the piston-chamber forming member fluid is discharged out the outer end of the stem of the piston element. The piston element includes resiliently deformable fingers carried on the stem extending radially outwardly from the stem to distal ends which provide a radially remote portion which is resiliently deformable between an unbiased position and deflected portions. The remote end portion extends circumferentially about the stem to provide in the unbiased position an outer radial extent of a constant radius about the stem.