The wet-pipe automatic sprinkler system is the oldest and most reliable type of automatic sprinkler system.  The automatic sprinkler system installed by Henry Parmelee in his New Haven piano factory in 1875 contained an alarm valve that provided for the operation of a bell or whistle when one or more of the sprinklers operated.  Thus, Parmelee can be credited with two major accomplishments: (1) developing the first practical and effective automatic sprinkler, and (2) perfecting the first effective wet-pipe automatic sprinkler system.

Because of its relatively simple design, the wet-pipe sprinkler system is the most effective and efficient type of sprinkler system available. The wet-pipe sprinkler system consists of water-filled pipes with standard upright, pendent, or sidewall sprinkler heads installed on the pipes. The distribution system of pipes with the sprinkler heads on the branch lines is connected to a suitable water supply of adequate capacity and pressure. In majority of cases, the water supply is from either a public or private water supply main.

The wet-pipe sprinkler system is activated by operation of the automatic sprinkler; this activation allows water to be discharged into the fire area. In turn, the flow of water from the sprinkler activates the alarm check valve on the main supply riser to the system. The alarm check valve then initiates the activation of water or electrically operated alarm devices that can be automatically arranged to summon the fire department.

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