Steam admission valve and variable clearance volume steam cylinder

In a steam engine, a cylinder containing a reciprocable piston, a steam admission chamber communicating with the cylinder through a circular valve port in an end wall of the cylinder, an annular surface portion of the end wall surrounding the port forming a valve seat in said chamber, a valve element in the chamber having an annular sealing surface to engage the valve seat, spring means biasing the valve element into seated position to close the valve port, and a substantially rigid valve lifter member fixed to an uppermost portion of the piston, the piston, the valve element, spring means and valve lifter member being disposed on a common longitudinal axis, the lifter member having an abutment surface for engaging a cooperable surface on the valve element to unseat the valve element against the force of said spring means to open the valve port, the spring means having sufficient strength to maintain the abutment surface and the cooperable surface in engagement while the valve element is unseated, said abutment surface and said cooperable surface comprising non-planar conforming surfaces of revolution coaxially related to said valve seat, whereby the sealing surface of the valve element is maintained both parallel to and centered in relationship to the valve seat in the seating of the valve element.