Figure 8-20.Water spray nozzles.
down the switch response to the surge is not used.
Various retarding techniques are used, some
associated with the sprinkler piping and some with
the water-flow detector.
The pressure increase type of water-flow
detector (fig. 8-21) comes in numerous styles. It is
found in wet or dry pipe sprinkler systems. The
usual arrangement for switch actuation includes a
sealed accordionlike bellows that is assembled to a
spring and linkage. The spring-tension setting
controls the pressure at which the flow detector is
actuated. It can be field adjustable and/or factory
set to the desired pressure that activates the
electrical switch. If this pressure switch is to be
used on a wet pipe system, it is usually mounted at
the top of a retarding chamber. This reduces the
speed of pressure buildup at the switch. Other
styles of this switch incorporate a pneumatic
retarding mechanism within the detector housing.
The retard time is adjustable to a maximum of 90
seconds. Usual settings are in the range of 20 to 70
seconds. The retard switch is connected to the
alarm port of a wet sprinkler system alarm check
Figure 8-21.Pressure increase type of water-flow detector.
valve. It is usually set for a pressure range of 8 to
Pressure drop detectors can be used in wet
pipe sprinkler systems equipped with a check