Wet Pipe Systems

Wet pipe systems are the most common. As the name implies a wet pipe system is one in which water is constantly in the piping and under pressure. When a sprinkler activates water is immediately discharged onto the fire. Some of the advantages of a wet pipe sprinkler system are:   simplicity and reliability, relative low installation and maintenance cost, ease of modification and short term down time in the event of a fire The main disadvantage of wet pipe sprinklers are that they are not suitable for areas that may be expose to freezing conditions. Back                                                                                                                                                                Drawing

	Dry Pipe Systems
	A dry pipe system is one in which the pipes are filled with pressurized air rather than water. The air uses a mechanical advantage to hold back a device known as a dry pipe valve. In the event of a fire, a sprinkler head operates that air rushing out of the piping, releasing pressure on the dry pipe valve. As the air pressure in the piping decreases the mechanical advantage in the valve is diminished, the valve opens and water rushes to the open head and onto the fire. Their main advantage is the ability to use dry pipe systems in areas where freezing is possible. Some of the disadvantages are increased complexity, higher installation and maintenance cost and increased response time. Back                                                                                                                                                               Drawing

Deluge Systems

The third sprinkler system type is the pre-action system which employs the basic concept of a dry pipe system in that water is not normally in the pipes. The difference is that water is held out of the piping by an electrically operated valve, know as a pre-action valve. Valve operation is controlled by an independent system of heat, flame or smoke detectors. Two separate events must take place to initiate a water discharge. First the detection system must sense the heat, flame or smoke of a developing fire and then open the pre-action valve allowing water to flood the piping. Secondly, the individual sprinkler heads must be fused or activated by heat from the fire in order to allow the water to flow from the head. The primary advantage of a pre-action system is that a minimum of two separate actions must take place for water to be discharged, thereby providing an added level of protection against accidental discharge. The disadvantages of a pre-action system are high installation and maintenance cost, which potentially decrease reliability due to the systems complexity and modification difficulties caused by specific size limitations. A variation of the pre-action system is the deluge system. Basically a deluge system is a pre-action system with open sprinkler heads. Operation of the pre-action valve caused by the separation detection system allows water to immediately flow from all the sprinkler heads. Back                                                                                                                                                              Drawing