Bash valve
A bash valve is a valve within a piston engine, used to control the admission of the working fluid. They are directly actuated valves, operated by contact between the piston and the valve tip. Bash valves have the advantage of great simplicity, for manufacture and operation. Their disadvantages are that their opening and closing times are relatively crudely controlled, compared to other types of valve gear. The valve is usually constructed as a circular poppet valve with a conical seat, inserted into the cylinder from the outside. A protrusion on the inside is hit by the piston as it approaches top dead centre, forcing the valve open. Bash valves are usually held closed by the pressure of fluid in the reservoir behind them. There may be a light spring to assist closing when the reservoir is empty. For this reason they are used as inlet valves, not exhaust. An exhaust bash valve would have the cylinder pressure and the piston actuation both acting to open it, with nothing to close it. Steam engines Bash valves are not widely used in steam engines, although they are known. Most examples were applied to some form of uniflow steam engine; unlike the more