Positive displacement pump

Claim 1

A positive displacement pump having minimum head space comprising: a cylinder including a cylinder head having an inlet valve seat; an inlet valve movably mounted in said cylinder head, the head space side of said inlet valve being flush with the head space side of said cylinder head when said inlet valve is closed; an inlet valve guide means mounted adjacent said inlet valve for guiding and retaining said inlet valve; a piston rod having an inlet end and a piston actuating portion, said rod being movably mounted within and substantially coaxial with the longitudinal axis of said cylinder; a piston head with a transfer valve movably mounted thereon, said piston head being attached to said inlet end of said rod and having an aperture in a plane substantially perpendicular to the longitudinal axis of said cylinder and substantially parallel to the plane of said inlet valve seat so as to define a transfer valve seat, said plane of said aperture substantially coinciding with said plane of said head space side of said cylinder head when said piston rod is fully stroked and said inlet valve is closed so that said head space is minimized, said transfer valve comprising a conically edged disc portion, said transfer valve seat comprising the conical edge of an annular flange which is inwardly extended from said piston head at the end of said piston head nearest said inlet valve, the small diameter side of said disc portion mating substantially flush with the side of said annular flange nearest said inlet valve, the plane of said smAll diameter side substantially coinciding with said plane of said head space side of said inlet valve when said piston rod is fully stroked and said inlet valve is closed so that said head space is minimized, the edge of said disc portion mating with said conical edge of said annular flange when said transfer valve is closed; and a transfer valve guide means mounted adjacent said transfer valve for guiding and retaining said transfer valve.