Simply put, a flushometer is a flushing device that uses energy from a pressurized water supply system, rather than the force of gravity, to discharge water.
FLUSHOMETER VS. STORAGE TANKA flushometer differs from a storage tank in that water flows under pressure from the supply line directly to the flushometer, allowing for repeated operation. In contrast, a storage tank requires water to first accumulate in the tank, from which the water flows by gravity to flush the fixture.
Since the water passes through the flushometer under pressure, the fixture is quickly evacuated with a scouring action to ensure thorough cleansing for increased hygiene. These qualities, among others, are responsible for the popularity of flushometers in every type of commercial, industrial and institutional building.
TWO TYPES OF FLUSHOMETERSFlushometers are manufactured with two different designs - the diaphragm valve and the piston valve.
The theory of operation for both is fundamentally the same. Each has an upper chamber and a lower chamber communicating with each other by a small opening called a by-pass hole. The by-pass in both diaphragm and piston valves is a small hole or orifice that is no larger than a pinhole – measuring between 0.020” and 0.030” in diameter (about the size of the “period” in this sentence).
A flexible diaphragm separates the upper and lower chambers in a diaphragm flushometer. A molded cup separates the upper and lower chambers in piston flushometers.
DESCRIPTION OF DIAPHRAGM OPERATIONWhen in the closed position, the diaphragm divides the valve into an upper and lower chamber with equal water pressures on both surface areas of the diaphragm. The greater force caused by the larger surface on top of the diaphragm holds it closed on the valve main seat.
Movement of the handle in any direction pushes the plunger, which in turn tilts the relief valve and allows water to escape from the upper chamber. The force against the lower chamber — now being greater — raises the working parts as a unit, allowing water to flow down through the valve outlet to evacuate the fixture.
While the valve is operating, a small amount of water flows through the by-pass of the diaphragm, gradually refilling the upper chamber and equalizing the pressure and increasing the force on the larger area on top of the diaphragm for quick, repeated operation. As the upper chamber gradually fills, the diaphragm returns to a closed position on the main valve seat, closing the valve.
DESCRIPTION OF PISTON OPERATIONA double molded cup divides the valve into an upper and lower chamber, with equal water pressures in both chambers when the valve is in the closed position. The greater force on top of the piston holds the valve closed on the main seat.
A slight movement of the handle in any direction pushes the plunger, which in turn tilts the relief valve and allows water to escape from the upper chamber. The water pressure (and force) in the lower chamber — now being greater — raises the piston from the valve main seat, allowing water to flow down through the valve outlet to flush the fixture.
While the valve is operating, a small amount of water flows through the by-pass, gradually filling the upper chamber and equalizing the pressure for quick, repeated operation. As the upper chamber gradually fills and increases hydraulic force, the piston returns to the valve main seat to close the valve.
MANUAL VS. SENSOR OPERATIONThere are two means of actuation for a flushometer - manual and sensor operation. Manual flushometers require the user to depress the handle of the unit to start the chain of events that complete the flush. Touchless, sensor-operated flushometers require an electronic power source to actuate the flushing mechanism once the sensor detects the user has walked away from the flushometer.
For these electronic flushometers, the power comes from either a wired-transformer source or replaceable batteries. Commonly, battery-operated flushometers are installed for retrofit applications, as restrooms are not normally wired behind the wall where the plumbing system is situated unless specified during initial design.
Newer buildings often are designed with electrical wiring to connect to the plumbing system (hard wired) because of the emergence of sensor-operated flushometers during the past two decades. Hard-wired flushometers provide more protection against vandalism and abuse because the mechanics of the unit are hidden behind the wall.
NON-HOLD OPEN HANDLES VS. HOLD-OPEN HANDLESAnother distinguishing factor between flushometers - besides the diaphragm and piston mechanics - is the non-hold open and hold-open handle type. (Note: some flushometers do not incorporate a non-hold open feature.)
Non-Hold Open Handles
Non-hold open flushometers complete a flush cycle and shut off, regardless of whether the handle is held down or released.
For example: When the valve is flushed, the bottom of the relief valve stem is carried (by the diaphragm or piston) ABOVE the plunger. However, even if the handle is held down, which keeps the plunger in its extended position, the valve is allowed to close, the relief valve stem drops down on top of the handle plunger and telescopes within itself. This non-hold open feature permits the working parts to return to the main valve seat, shutting off the valve upon completion of its normal cycle.
Hold-open flushometers typically have longer, inflexible relief valve stems so that the handle plunger and the stem are engaged constantly. As a result, the valve can be held open if the handle remains depressed, and since the flushometer is directly connected to the supply line, water will flow freely until the working parts are able to return to the main valve seat.
In the interest of water conservation and cost effectiveness — especially where the water supply is limited — this difference in flushometer design is worthy of consideration.
CONTROL STOPSThe purpose of the control stop is to control the flow rate of water through the valve. Control stops also act as a local water service shut-off and keep the valve pressurized in case of a momentary loss of water supply pressure.
Most flushometers are equipped with a back-check control stop to serve four important functions:
Function 1: To regulate the flow rate of water entering the flushometer
The control stop permits regulation of water flow to the fixture being served. The control stop is opened (counter clockwise) for lower pressures and closed (clockwise) for higher pressures.
Function 2: To shut off the water supply to the flushometer
The control stop can be closed completely to shut the water off at the flushometer for repair and maintenance without disturbing the water supply to other fixtures.
Function 3: To cushion and quiet the flow of water
The control stop is designed to direct the flow of water back upon itself, cushioning and quieting the flow, thus minimizing noise common to water supply systems.
Function 4: To prevent false operation of the flushometer when pressure in the supply line is lost and subsequently restored
The control stop back check allows the flushometer to remain under pressure at all times during pressure losses or negative pressure conditions in the supply line. When pressure is restored, the flushometer is ready for normal use.
VACUUM BREAKERSU.S. Government specifications and many international plumbing codes stipulate that every flushometer connected to a potable water supply for use with a water closet or urinal be equipped with a vacuum breaker to prevent back siphonage. When flushometers are installed on a non-potable water supply system, vacuum breakers are not required.
A vacuum in the supply lines can cause back siphonage when:
1. Water supply fails
2. A main breaks
3. Fire hoses draw heavily on the available water supply
4. A line is shut off and drained
5. Water pressure is low and a heavy drain occurs at a low point
Vacuum itself can do no damage to the piping system. However, there is potential of a dangerous health hazard if, during vacuum conditions, the piping system is exposed to a source of polluted water. In such cases, polluted water is siphoned from the fixture back into the fresh water supply line. This newly polluted water will now be drawn from drinking fountains and faucets for drinking and household use, creating the possibility of a very serious health hazard.
Obviously, a preventative course of action would be to eliminate all possible direct connections of the water supply with any source of contamination.
Therefore, most flushometers are furnished with a vacuum breaker flush connection that houses the vacuum breaker to prevent back siphonage. These vacuum breaker flush connections are supplied with tube sizes to meet the spuds commonly found on most water closets and urinals.
PRINCIPLE OF OPERATIONVacuum breakers are designed to allow the passage of water to properly flush the fixture and to react instantaneously to the slightest vacuum that might occur in the supply line. The flexible rubber sleeve accomplishes this. During the flushing action, the rubber sleeve is expanded to cover the air ports (vents) in the flush tube. While under vacuum conditions, the rubber sleeve collapses upon itself to prevent back siphonage.
WATER FLOW RATES AND PRESSUREThe required flow rate (gal/min) is established by the requirements of the fixture - not the flushometer. If the supply pipes are properly sized, the water passing through the flushometer will permit the fixture to operate efficiently.
Some flushometers do not require water flow regulation at installation because they are engineered to deliver a proportionate amount of water over a broad pressure range through the valve outlet during a flushing cycle. That means a proportionate amount of water flows through the by-pass into the upper chamber of the valve, regardless of variations in pressure. A constant ratio of water passes through the valve so that the volume of water delivered is the same for each operation.
Peter Jahrling is the director of design engineering for Sloan Valve Company, having been employed with Sloan for more than 25 years. He earned his BS/MS in engineering from the Illinois Institute of Technology and is a member of the Plumbing Manufacturers Institute (PMI). Peter can be reached at SloanEngineer@interlinegroup.com.