A high efficiency uniflow steam engine having automatic poppet valves yieldably based by fluid such as steam held under pressure within a cavity in the engine and a cutoff control for closing a steam inlet valve at any time selected stops the flow of steam into the cylinder. Proximate the end of the exhaust stroke, around 0.12 inch before TDC the cylinder is sealed to thereby compress residual steam as the piston clearance approaches zero; typically, 0.020 inch which raises cylinder pressure enough to open an inlet valve without making physical contact to push the inlet valve open with the piston thereby eliminating a tappet type of noise, shock and wear.

A high efficiency uniflow steam engine with automatic inlet and exhaust valves rather than camshaft operated valves includes an electromagnet and cooperating armature that actuates a cutoff control valve for closing a steam inlet valve at any time selected to stop the flow of steam to the cylinder. Approaching the end of the exhaust stroke typically 0.12 inch before TDC the cylinder is sealed thereby compressing the remaining residual steam down to a minute clearance approaching zero, for example, 0.020 inch to raise cylinder steam pressure enough to open the steam inlet valve without physical contact between the piston and the steam inlet valve thereby eliminating tappet noise, shock and wear.

A high efficiency uniflow steam engine having automatic inlet and exhaust valves rather than camshaft operated valves includes an electromagnet and cooperating armature that actuates a cutoff control valve for closing a steam inlet valve at any time selected to cut off the flow of steam to the cylinder. Approaching the end of the exhaust stroke, e.g., about 0.12 inch before TDC the cylinder can be sealed to thereby compressing the remaining residual steam down to a minute clearance approaching zero, for example, 0.020 inch raising cylinder steam pressure enough to open the steam inlet valve without physical contact between the piston and the steam inlet valve eliminating tappet noise, shock and wear.