A wet pipe sprinkler system is a sprinkler system employing automatic sprinkler heads attached to a piping system containing water and connected to a water supply so that water discharges immediately from sprinklers opened by heat from a fire.

Each sprinkler is activated individually when it is heated to its design temperature. Most sprinklers discharge approximately 20-25 gallons per minute (gpm), depending on the system design. Sprinklers for special applications are designed to discharge up to 100 gpm.

A dry pipe sprinkler system is a system with automatic sprinkler heads attached to a piping system containing air or nitrogen under pressure. The release of this pressure (as from the opening of a sprinkler) permits the water pressure to open a valve known as a dry pipe valve and the water then flows into the piping system and out of the open sprinkler head.

Dry pipe sprinkler systems are installed in areas where wet pipe systems may be inappropriate such as areas where freezing temperatures might be expected.

Deluge Sprinkler Systems

The arrangement of deluge system piping is similar to a wet or dry pipe system with two major differences:

A. Standard sprinklers are used, but they are all open. The activating elements have been removed so that when the control valve is opened water will flow from all of the sprinklers simultaneously and deluge the area with water.

B. The deluge valve is normally closed. The valve is opened by the activation of a separate fire detection system.

Deluge systems are used where large quantities of water are needed quickly to control a fast-developing fire. Deluge valves can be electrically, pneumatically or hydraulically operated.

A pre-action sprinkler system is similar to a deluge sprinkler system except the sprinklers are closed. This type system is typically used in areas containing high value equipment or contents and spaces which are highly sensitive to the effects of accidental sprinkler water discharge. The pre-action valve is normally closed and is operated by a separate detection system.

Activation of a fire detector will open the pre-action valve, allowing water to enter the system piping. Water will not flow from the sprinklers until heat activates the operating element in individual sprinklers. Opening of the pre-action valve effectively converts the system to a wet pipe sprinkler system.

In a pre-action system the piping is pressurized with air or nitrogen, monitoring of this air pressure provides a means of supervising the system piping. Loss of the supervisory air pressure in the system piping results in a trouble signal at the alarm panel.