Crawford Sprinkler Company

A Dry Pipe Sprinkler System is a fire-protection system which utilizes water as an extinguishing agent. The system piping from the Dry Pipe Valve to the fusible sprinklers is filled with pressurized air or nitrogen. An air check system is a small dry system which is directly connected to a wet pipe system. The air check system uses a dry valve and an air supply but does not have a separate alarm. The alarm is provided by the main alarm valve.
A Dry Pipe System is primarily used to protect unheated structures or areas where the system is subject to freezing. Under such circumstances, it may be installed in any structure to automatically protect the structure contents and/or personnel from loss due to fire. The structure must be substantial enough to support the system piping when filled with water. One system may protect as much as 52,000 sq. ft. (4830.8m2) in a single fire area. The system should be designed by qualified fire protection engineers in conjunction with insuring bodies.


There are several types of preaction systems, but all employ closed sprinklers in the sprinkler piping. The detection system may be hydraulic, pneumatic or electric, and may be actuated by manual, fixed-temperature, rate-of-temperature-rise or other means. Detection systems operate before the sprinklers fuse and give an alarm. Because preaction systems are often used in freezing areas, electrical and pneumatic detection systems are by far the most common. Preaction systems are usually supervised. The purpose of supervision is to monitor the integrity of the system. Air or gas under pressure is maintained in the sprinkler and release piping. If the sprinkler or release piping or a sprinkler head is broken, the pressure will be reduced and an alarm will sound. There will also be an alarm due to low air or gas supply pressure. Electrical equipment can be similarly supervised. Hydraulic release system or supply pressure may also be supervised.
Preaction systems operate in several of ways and perform a variety of functions. A summary of the most common types of Viking preaction systems follows:
Non-Interlock Preaction System: This preaction system utilizes a Viking deluge, which may be opened either by the fusing of a sprinkler in the sprinkler piping or by the operation of the detection system. The sprinkler piping contains air or gas under pressure. If the detection system does not operate, the sprinkler system will operate as a dry pipe system. If the sprinkler piping is broken or the sprinkler operates, the valve will open and water will flow. If the detection system operates due to fire, damage, or malfunction, the valve will open, but the water will be contained in the sprinkler piping. The system is supervised to indicate low air pressure. The objective of this system is to fill the sprinkler piping with water prior to the fusing of a sprinkler, thereby permitting more rapid fire attack.
Single-Interlocked Preaction System: The single interlocked preaction system requires operation of the detection system to trip the Viking deluge valve and fill the system with water. It also utilizes supervisory air pressure in the system piping. Water will then be discharged on the fire when the sprinklers fuse. If the sprinkler piping or sprinkler is broken, a supervisory alarm will sounds, but the valve will not open. If the detection system operates due to fire, damage, or malfunction, the valve will open, but the water will be contained in the sprinkler piping. If the detection system does not operate, the valve will not open. Supervision is generally used since control of accidental discharge is usually desired. The single interlocked preaction system is commonly used where it is desirable to have water available at the sprinkler when the sprinkler fuses and where the sprinkler piping is subject to damage. The most common applications are large dry systems that exceed the capacity normally permitted on a dry valve, and in a system applications where it is important to control accidental water discharge due to damaged sprinkler piping.
Double-Interlocked Preaction System: The Double-Interlocked Preaction System utilizes a detector system and pressurized air or gas in the sprinkler piping. This system utilizes the Viking deluge valve and is arranged so that the valve will open only when both pressure reduced in the sprinkler piping and the detection system operates. If the detection system operates due to fire, damage, or malfunction, the valve will not open, but an alarm will sound. If the sprinkler piping is damaged or sprinkler is broken or fused, the valve will not open but a supervisory alarm will sound. The operation of both a sprinkler and a detector (or release) is required before the valve will open, allowing water to enter the system piping. Because pressurized air or gas is available in the output piping, the system is usually supervised. The Double-Interlocked Preaction System is commonly used in freezers where flooding of the pipe can have serious consequences and in system applications where it is important to control accidental discharge of the system.
Firecycle System: This is a special type of supervised recycling system. For further details, see the Firecycle section.


A Deluge System is a fixed fire-protection system which totally floods an area with pressurized water through a system of piping and open nozzles or sprinklers. The system piping is empty until the Deluge Valve is activated by a hydraulic, pneumatic, electric or manual release system.

Regular Deluge Systems may be required to protect extra-hazard occupancies by creating a fire buffer zone or by cooling surfaces to prevent deformation or structural collapse. Examples: storage or process areas containing substances having a low flash point; areas in which fire may spread rapidly; tanks containing combustible solutions, transformers, equipment pits or product handling systems. Systems should be designed by qualified fire-protection engineers in conjunction with the approving bodies having jurisdiction. Foam-water de luge systems are those using foam-water sprinklers or spray nozzles and an air-foam concentrate which is in troduced into the water at controlled rate on the system side of the deluge valve. Foam water systems are used to control and/or extinguish fires which require a smothering and cooling agent. Examples are: extraction plants, aircraft hangars and areas where flammable-liquid spill fires may occur.
The deluge valve prevents water from entering the system piping until required. The deluge valve is kept closed by a pressurized upper valve chamber. The pressure is maintained through a restriction on the service side. This upper chamber is also connected to the release line. When the pressure is relieved from the upper chamber through the release line, the clapper is lifted by the water pressure under the clapper. Water floods the system and rings alarm.