(Compound, Double Acting, Piston Valve Steam Engine) White The image (left) shows the White compound pistons, the Low Pressure piston being larger because the steam entering the second stage steam occupies more volume leaving the High Pressure cylinder than it did when entering: the LP Valve is larger for the same reasons. Piston valves function identically to the “D” valve; the outer lips uncovering passages admitting the flow of steam and exhaust. Steam pressure acting on the face of “D” valves forces them against their seats, causing friction and wear; pressure acts on round piston valves from all directions, yielding no thrust. This thrust seals slide valves tightly while piston rings under The Stanley engine is inherently self-starting, the double-acting crankpins set 90 degrees apart ensure that, at long cutoff, at least one end of one cylinder will always be in position to accept steam and turn the engine.  Such long cutoff is inefficient but makes for great torque, a necessity when moving a vehicle from a standing start without a variable speed transmission. Even though also having two double-acting cylinders set 90 degrees apart, the compound arrangement prevents the White from self-starting.  If the High Pressure cylinder is not in a position to receive steam, it cannot pass this steam onto the Low Pressure cylinder and thus neither will turn the crankshaft. Compound engines can be made self-starting with a simpling valve, a device which redirects HP exhaust away from the second stage receiver and instead to exhaust while connecting the second stage receiver to the boiler.  In effect it converts the non-self-starting compound into a self-starting simple engine with two different sized cylinders.  The large LP cylinder generates great starting torque but also imposes equally great stress upon the engine. (not representative of White simpling valve) The White engine is very similar to the Stanley and yet quite different. The Stanley crosshead, connecting rods and crankshaft are contained in an open framework whereas the White keeps them neatly enclosed and protected. The Stanley is a “simple” engine with slide valves; the White is a compound with piston valves. Both are two-cylinder, double acting engines.