The engine may be double-acting but preferably consists of two single-acting cylinders separated by a common block containing the oil nozzles so that the piston rod is always in tension.
The air for flushing and combustion is supplied by any suitable form of rotary blower driven by an independent oil engine of the same type as the main engine, which latter may also be utilised to drive a stage compressor for supplying the high-pressure air, and, when used on board ship, the ship's dynamo.
The engine is claimed to be capable of being readily reversed and to be especially suitable for the propulsion of ships of war. The pistons are grooved to direct the air and exhaust gases, and have projections to close the ports at the end of the in-stroke. The piston rod comprises a tube enclosing a rod which is reduced in diameter at regular intervals, the flanges between the reduced parts being grooved for the passage of cooling water through the tube.
The stuffing box consists of a box containing a number of split rings held against the rod by their own elasticity and by springs. The rings are situated between solid rings spaced by other rings and retained by a screw cover. Each cylinder is provided with an oil-spraying valve, both worked by one cam which, through levers, links and a crosshead, lifts both the oil valves against its springs and the valve for the supplying of high pressure air for spraying.
For reversing, the oil is cut off and the speed of the engine is checked by moving a block along a lever to engage a balanced valve which is opened and allows the compressed charge to escape from the cylinder at the end of the in-stroke, and then closes causing a vacuum to be produced in the cylinder during the out-stroke.
The engine is thus brought to rest, and compressed air being then admitted first by hand to one of the cylinders, and then, through suitable valves, to all of them the starting of the engine is effected in the opposite direction. The cam adjusts itself angularly automatically for the new direction of running through an arm on its shaft driven by one of the two blocks on a disc driven from the crankshaft.
The cam is made up of several rings each having a swell of different length, so that by moving it in an axial direction the period of admission of the fuel may be regulated. To ensure the cam always opening the valve at the same time in both directions of running, each ring, except that one having the narrowest swell has a key-way of a different width and adjusts itself automatically.