Preaction sprinkler systems are equipped with automatic sprinklers and are used where it is important to prevent the accidental discharge of water. These systems may also be used where an alarm is desired in advance of sprinkler operation or where it is desired to minimize the water delivery delay inherent in a standard dry-pipe system. For this reason, the following factors shall be carefully assessed: detector spacing and sensitivity, sprinkler piping arrangement and ceiling construction. Supervisory pressure is maintained in the sprinkler piping of a preaction sprinkler system. A trouble alarm sounds if the supervisory pressure is not maintained; however, such a condition will not cause the automatic water control valve to operate. Generally, a single check valve is installed downstream of the automatic water control valve to contain the supervisory pressure. Except for the addition of a single check valve and the use of automatic sprinklers, components of preaction sprinkler systems are identical or similar to those of deluge sprinkler systems. The water supply is held back by a water control valve which is operated manually or automatically by the actuation of a fire detection system. The fire detection system is required to be one of the following types: hydraulic rate-of-rise, pneumatic rate-of-rise or electric.