Preaction Sprinkler Systems
Argus Fire Protection has considerable experience with the design, on-going service, maintenance, testing and compliance management of specialist fire sprinkler systems such as preaction sprinkler systems. We are able to offer a full range of specialist systems of this type and the backup service to support your installation.

What is a Preaction Sprinkler System?
Preaction sprinkler systems are utilised in situations where a greater level of security against false discharge of water is required.

A preaction sprinkler system is a form of dry pipe sprinkler system incorporating water discharge pipework fitted with closed sprinkler heads, but charged with low pressure gas for supervision purposes. Water entry to this piping system is controlled by an independent detection system, usually either electric (e.g. heat detectors, smoke detectors, or other detectors suited to the specific risk being protected) or a further system of small diameter piping with closed sprinkler heads charged with gas for control purposes.

Before water may be discharged it is necessary that both the detection system and the sprinkler heads on the discharge pipework operate.

Preaction sprinkler systems are categorised by their style of operation (generally either single interlock or double interlock) and their type of detection (generally electric or pneumatic) as described below.

Types of Preaction Sprinkler Systems
The basic types of preaction sprinkler systems and their typical uses are described below.

Single Interlocked
With a single interlocked preaction sprinkler system the preaction control valve opens and charges the discharge pipework with water on operation of the detection system. Water is not discharged from the discharge pipework until one of the closed head sprinklers on the discharge pipework operates.

The discharge pipework is normally charged with gas at low pressure for supervision purposes to ensure that the pipe remains closed. If a sprinkler on the discharge pipework is operated without the detection system operating then the preaction system will provide indication of a defect state, so that the service agent can be brought to site to repair the system.

  

Double Interlocked
With a double interlocked preaction sprinkler system the preaction control valve does not open until both the detection system and one of the closed head sprinklers on the discharge pipework operates.

Double interlocked preaction sprinkler systems are more complex than single interlocked sprinkler systems and are therefore considered to be less reliable. In addition because the preaction control valve does not open until both the detection system and a closed head sprinklers on the discharge pipework operate there is a longer delay before water is discharged onto the fire.

The New Zealand automatic fire sprinkler standard (NZS4541) only permits the use of double interlocked preaction sprinkler systems in freezers and other similar environments where it is undesirable to permit water to enter the discharge pipework until the after the sprinklers have been activated due to the risk of and damage associated with freezing water in the pipework.

Pneumatic Detection
The most common type of detection for a preaction sprinkler system is pneumatic detection where a system of small diameter piping with closed sprinkler heads charged with gas (normally dry air) is distributed throughout the enclosure for detection and control purposes. When a sprinkler on the detection network operates, the gas pressure is lost and the preaction control valve operates.

The New Zealand automatic fire sprinkler standard (NZS4541) favours the use of pneumatic detection over other means of detection.

Electric Detection
The New Zealand automatic fire sprinkler standard (NZS4541) only permits the use of electric detection in limited circumstances such as freezers and then only with the specific approval of the Sprinkler System Certifier.