Pre Action Fire Sprinkler Systems

Type A
Like dry pipe systems the pipes are filled with air (but at lower pressure) and the water is only let into the pipes when the detection systems is/are alerted. Pre-action Type A systems are used where it is not acceptable to have the pipes full of water unless there is a fire, for example in areas containing high value equipment or contents and spaces which are highly sensitive to the effects of accidental sprinkler water discharge.

Type B
Like dry pipe systems the pipes are filled with air and the water is let into the pipes either a) when the detection systems is/are alerted or b) should sprinklers operate. Pre-action Type B systems are used usually in storage facilities where freezing could be a problem.