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 valve. It is usually set for a pressure range of 8 to 15 psi.

Figure 8-21. - Pressure increase type of water-flow detector.

Pressure drop detectors can be used in wet pipe sprinkler systems equipped with a check