Expanded piston cup and improved spreader

Claim 1

An expanded piston cup assemblage for use in the cylinder of a pump comprising: a. resilient annular expanded piston cup means having an annular bearing surface for slidably engaging the wall of the cylinder, an inner cup portion, and a lower surface; b. backing means engagiNg said lower surface for providing backing strength to said cup means, said backing means having an outer dimension slightly smaller than that of said cup means and out of contact with the wall of the cylinder, said backing means further including a closed internally threaded bore; c. spreader means disposed in said inner cup portion for exerting pressure on said inner cup portion for maintaining the slidable engagement between said bearing surface and the cylinder wall, said spreader means including body means having a predetermined depth dimension, an annular outer surface, and upper and lower surfaces, said lower surface adapted to substantially conform to said inner cup portion of said piston cup means, said body means including two diametrically opposed fluid ports extending a predetermined depth into said body means from said upper surface for permitting flow therein, a first annular groove having a generally arcuately shaped annular surface formed about the surface of said spreader means, an annular pressure groove formed inwardly of said first annular groove and being in fluid communication with said fluid ports, and an annular distended biasing O-ring with substantial resiliency being retained in said first annular groove and having portions thereof extending radially outwardly beyond the annular outer surface of said first annular groove, said O-ring being forced outwardly from said first annular groove in response to fluid under pressure disposed in said fluid ports and said pressure groove for exerting increased outward pressure on the surface of said inner cup portion for urging said annular bearing surface against the cylinder wall during the pressure stroke portion of a pumping cycle, said O-ring providing a resilient biasing force on said surface of said inner cup portion for preventing said bearing surface from flexing inwardly out of contact with the cylinder wall during the suction stroke portion of the pumping cycle; and d. coupling rod means connected to said internally threaded bore for coupling said piston cup means, said backing means, and said spreader means together.