Generally takes the form of a wet pipe (line continuosly flooded) on to which are connected a number of sprinkler head. These heads consist of a valve held shut by a high expansion fluid filled quartzoid bulb.A small air space is incorporated.
Water is supplied from an air pressurised water tank ( thus the system functions without electrical power), this water is fresh water to minimise damage. The tank is half filled with water and the rest is compressed air at pressure sufficient to ensure that all the water is delivered to the highest sprinkler at sprinkler head working pressure. Once this source of water is exhausted, falling main pressure is detected by a pressure switch. This activates a sea water supply pump. A valve is fitted on the system to allow proper testing of this function. After sea water has entered the system proper flushing with fresh water is required to prevent corrosion
A shore connection may be connected to the system to allow function during dry-dock