Crispin CR-PL10A 2" Pressure Air Release Valve Systems under pressure can be vented of accumulating air with the use of Pressure Air Release Valves. These should be mounted on the system at all high points, and downstream from these points where the velocity of the liquid carries the air or gas slightly beyond the crest. On lines with little gradient, valves should be placed every half mile or so, at the discretion of the engineer. Crispin Type “N” is for normal use in water below 150° F, and features a PVC seat. Crispin Type “P” is for use with all types of fluid, and is supplied with a steel seat. Both are supplied with a Buna-N rubber plunger. For special applications, an optional stainless steel seat with a Buna-N plunger is available. When a valve is used in a system where a vacuum is desired, such as in a pump prime, an optional vacuum check unit is offered that will prevent air from re-entering the system