A flushometer valve flushes a commercial toilet or urinal straight from the supply line, with no tank. A handle or sensor opens the valve, a measured burst of water runs, and line pressure closes it again. That is why it needs a one-inch supply, steady pressure and an adjustable control stop.
What does a flushometer do that a tank does not?
A flushometer flushes with supply-line pressure, so the pipe has to do the work a tank's stored water would do. EPA describes flushometer-valve toilets as "tankless fixtures" with a lever- or sensor-activated valve that "releases a specific volume of water at a high flow rate directly from the water supply line to the bowl."
The same EPA page adds the catch. These fixtures "rely on larger diameter water supply piping and high water supply line pressures to remove waste." That is why you see them in "public-use facilities and high-use commercial settings." There is no tank to refill, so the next person can flush right away.
What happens inside when you press the handle or the sensor fires?
In a diaphragm-type valve, the diaphragm is the moving part that opens and closes the main passage. Zurn's own sheet for the Aquaflush Z6000 lists a "dual seal quiet diaphragm and clog resistant by-pass." Sloan describes its Royal valve as a "PERMEX Synthetic Rubber Diaphragm with Dual Filtered Fixed Bypass."
Here is the sequence in a diaphragm valve, in short. Supply pressure holds the diaphragm closed. The handle, or a solenoid on a sensor valve, lets the pressure above the diaphragm bleed off. Supply pressure then lifts the diaphragm and water runs to the fixture. The small bypass refills the space above the diaphragm, and the diaphragm settles back down and ends the flush. Piston-type valves do the same job with a piston. Our page on a Sloan flushometer that keeps running shows what goes wrong when that refill step fails.
The code lines up with this. The 2024 IPC says that "the valve shall automatically complete the cycle of operation, opening fully and closing positively under the water supply pressure." It also says "Each flushometer valve shall be provided with a means for regulating the flow through the valve." That regulating means is the control stop, covered in how to adjust a flushometer.
What supply pipe and pressure does a flushometer need?
Enough of both, and more than a tank toilet. Table 604.3 of the 2024 IPC, as adopted by Phoenix, sets the design flow and pressure at the fixture supply outlet. For a siphonic flushometer-valve water closet it lists 25 gpm at 35 psi. A blow-out flushometer water closet is listed at 25 gpm and 45 psi. A flushometer-valve urinal is listed at 12 gpm and 25 psi.
Table 604.5 sets the minimum fixture supply pipe: 1 inch for a flushometer-valve water closet and 3/4 inch for a flushometer-valve urinal. Sloan's spec sheet for one Royal sensor model also lists a 1-inch supply pipe and a flowing operating pressure of 15 to 80 psi, then adds that "specific fixtures may require greater minimum flowing pressure."
Zurn's Z6000 sheet gives a recommended range of 10 to 100 psi and says "most low consumption fixtures (1.28 and 1.6 gallon) require a minimum of 25 psi running pressure through the valve." The numbers differ by model and bowl, so the valve and fixture instructions govern. The IPC also says flushometer valves "shall not be used where the water pressure is lower than the minimum required for normal operation."
What else is on the valve?
Four parts matter to anyone maintaining one:
- Control stop. The fitting where the supply pipe enters. It shuts off one valve for service and sets the flow.
- Vacuum breaker. It keeps used water from being pulled back into the supply. The IPC requires vacuum breakers on flushometer valves to meet ASSE 1001 and to be accessible. See do urinal flush valves need a vacuum breaker.
- Actuator. A handle on a manual valve, or a sensor and solenoid on an automatic one. EPA notes sensors "provide no additional water efficiency benefits," but they give a hands-free option.
- Diaphragm or piston kit. The wear part that sets the gallons per flush.
Why this matters when something goes wrong
Because the valve runs on line pressure, a weak or never-ending flush is often a supply or valve-internals problem, not a bowl problem. Start with a weak commercial flushometer flush or a sensor toilet that will not flush. If you are weighing the two designs for a restroom, flushometer vs tank toilet compares them. HQ is licensed and insured and gives free estimates on commercial restroom plumbing.