A
high pressure piston for use within a liner for a
reciprocating pump comprises an elastomeric seal and a metallic annular bearing ring having relatively
high heat conductivity compared to the liner and seal. During the pump's pressure
stroke a portion of the bearing ring elastically expands radially to narrow or close the
extrusion gap. Narrowing the gap decreases the tendency for
extrusion of
piston seal elastomeric material, while closing the gap tends to block
elastomer extrusion and establish
sliding contact between the bearing ring and the liner.
Sliding contact between the bearing ring and liner prevents portions of the
piston hub (e.g., a transverse
flange) from contacting the liner and damaging it. The heat-conductive bearing ring improves
scavenging of frictional heat near the extrusion gap, extending the service life of piston seal
elastomer while reducing bearing ring and liner wear. Under reduced pressure on the pump's return
stroke, the bearing ring elastically contracts radially, slightly widening the extrusion gap. On the pump's return
stroke the slightly wider extrusion gap allows cooling water directed generally toward the proximal
flange of the piston hub to better cleanse, as well as cool, the liner wall.