The common stopcock is the simplest form of rotary valve. There is normally a bung or stopcock that allows draining of the crankcase before starting. It has a stopper at the top and stopcock (tap), at the bottom. A stopcock may be included to permit the desiccator to be evacuated. Robison's siren consisted of a stopcock that opened and closed a pneumatic tube. The resulting material may be interfaced to an external device via a stopcock intermediate. They are fitted with a stopcock which allows the flow to be controlled. In that book Winkler describes his invention of the three-way stopcock. The quantity of gas consumed by each burner was regulated by a stopcock. Stopcock grease is always used in high vacuum applications to make the stopcock air-tight. The stopcock was apparently driven by the rotation of a wheel.