The charge may be introduced at any desired pressure and a valve or cock on the supply pipe may be controlled by hand or by a governor. The auxiliary inlet valve is opened slightly before the closure of the horizontal or inclined ports by the piston, and the time of closing may be delayed by a governor to reduce the charge in proportion to the load.
The air and fuel may be introduced separately through the main and auxiliary inlets, and the richness of the charge can then be varied by controlling the inlet valve. This latter valve may be held open during the nearly the whole of the in-stroke at starting to reduce compression; or it may be held open and compressed air be admitted through a port on the down-stroke and discharged through the same port on the up-stroke.