Table 5-5.Operation of Diaphragm FlushometerContinued
As the valve lifts the diaphragm, water begins to
flow slowly through the bypass orifice until the
pressure rises enough to equalize the pressure in the
upper and lower chambers, seating the valve.
Figure 5-43.Piston-type flushometer valve.
dashpot chamber. This forces the piston assembly down
onto its seat and stops the water flow. The closing of the
valve is regulated by a screw that controls the amount of
time the valve stays open.
Flush valves give years of adequate and trouble-
free operation when they are properly installed and
maintained. Continuous flow of water through a piston
type of flush valve is almost always caused by failure
of the relief valve to seat properly or by corrosion of
the bypass valve. In both cases, there is not enough
force on the piston to force it to seat. If the relief valve
fails to seat as it should, the leakage may be enough to
prevent the upper chamber of the valve from filling,
and the piston remains in the OPEN position.
Inspect the relief valve seat for dirt or other foreign
substances that may be causing the relief valve to tilt;
disassemble the piston, wash the parts thoroughly, and
reassemble. Replace washers that are worn, making
sure that the surface upon which the washer sets is
perfectly clean; scrape off old rubber if any sticks to
the metal surface.
Corrosion of the bypass valve in the center of the
top plate also causes continuous flow; the water cannot
pass into the upper chamber of the valve, and no force
is exerted on the piston to move it downward to its seat.
Very dirty water passing through the system can clog
the bypass and deprive the upper chamber of water.
When pipelines in a new installation are not
thoroughly flushed before they are placed in operation,
the pipe dope or dirt in them can stop up the bypass
Likewise, in a diaphragm valve, if chips or dirt
carried by the water lodge between the relief valve and
the valve seat, the relief valve cannot seat securely.
The water leakage prevents the upper chamber of the
valve from filling with water. The valve then remains
in the OPEN position, since there is no pressure to
force the diaphragm to its seat.
Short flushing can occur in a diaphragm type of
valve. If the valve seat, diaphragm, and guide cover
have not been tightly assembled, you should
reassemble the valve to ensure proper operation.
Sometimes you may find the bypass tube has been
tampered with, enlarging it so the water passes rapidly
into the upper chamber and closes the valve before the
desired volume is delivered. Also, someone may have
oiled or greased the valve parts to make the valve
operate more easily. What actually happens is the oil or
grease swells and ruins the rubber parts, interfering
with the action of the valve.
Another commonly used unit is the pressure-
valve-head flushometer (fig. 5-44). The most common
problem with this type of flushometer is the rubber
cap. To replace the rubber cap is a simple task; remove
the retaining screws, lift out the plate, and remove and
replace the cap.
Q15. What are the two types of flushometers used by