It is the use of the pressurized water supply that gives a flushometer a performance advantage over a tank toilet in commercial applications.
In a tank toilet, the water used for the flush is first accumulated in the tank. The water flows by gravity into the fixture when the tank toilet is flushed. The energy behind the flush is created by the weight of the water in the tank. Because flushometers rely on the pressure and flow from the supply piping, there is more energy behind the flush, which is important in a commercial application.
Flushometers also reset faster than gravity toilets (there is no refill time), another important requirement in a commercial installation. Gravity tanks will not be the subject of this white paper.
Flushometers are manufactured in two different technologies -- diaphragm and piston. The theory of operation in each is fundamentally the same. Each has an upper control chamber and a lower chamber connected by a bypass. The bypass connecting the upper control and lower supply chambers in both the diaphragm and piston valves is a small hole or orifice that is no larger than a pin hole, typically measuring between 0.020 inches and 0.030 inches in diameter. A flexible rubber disk separates the upper from the lower chambers in a diaphragm flushometer; a molded cup separates the upper from the lower chambers in the piston flushometer.