Potter Releasing Systems - Manual (Page 18)

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#2. Wet System With An Alarm Check Valve:
This type of system has an alarm check valve, the valve is basically a check valve with an alarm port. The main
purpose of the alarm check valve is to ring a mechanical bell called a water motor gong. The valve should, (if
properly maintained), help hold the system pressure steady and reduce the possibility of false alarms. Under
normal circumstances, the clapper of the valve is closed, blocking the alarm port, maintaining the system
pressure, and preventing the sprinkler system water from leaking back into the city supply. When a sprinkler
opens due to fire, or there is a large surge in the city pressure, the clapper of the valve opens. The alarm port is
now exposed to the incoming water supply. When the pressure at the switch reaches 6 psi, the pressure switch
trips, or the retard time starts on the pressure switch with built in retard. This alarm port may be piped to the
outside of the building through a water motor gong.
These systems can use a vane type flow switch with a retard or they can use a pressure type flow switch. The
pressure type flow switch would be installed on the alarm port, in line with a water motor gong if one is being
used. The pressure switch must either be installed on top of a retard chamber, (see Fig. 3), or a pressure switch
with a built in retard, (see Fig. 4), must be used to prevent false alarms due to water surges. There must be an
automatic drain on this line to allow the water to drain and the pressure to drop back to zero so the pressure
switch can reset after a surge or activation of the alarm valve.
Pressure type flow switches can be installed without disabling the sprinkler system. Since they are installed on
the alarm port, there is no pressure or water present under normal circumstances. The sprinkler system does not
have to be drained, they can be installed without shutting off the water supply. Therefore the sprinkler system is
never out of service.
Retard chambers are metal containers that fill with water when there is a surge in city pressure. They absorb
the pressure increase thereby allowing the pressure switch to only operate in an actual alarm condition. There
is an automatic drain at the bottom of the chamber to allow the surge to drain out. Retard chambers require
maintenance to make sure that the drain stays clear and doesn’t get clogged with rust or corrosion. If a surge
does not drain from the retard chamber before another surge happens, the retard chamber may fill causing the
pressure switch to send a false alarm.
A pressure switch with a built in retard allows the system to remain operational at all times, and eliminates the
maintenance required on the retard chamber. An automatic drain is still required to relieve the pressure on the line.
Note: All water control valves shall be supervised per NFPA13 2010 8.16.1.1.2.1. Pressure type flow switches
must be installed before any shut-off valve, or such valve must be electronically supervised.