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Page 6 of 20 TFP1020 This action permits water flow into the Operating system piping and subsequently to be Maximum System Air discharged from any open sprinklers. Water Supply Pressure Principles Also,with the Clapper Assembly open, Pressure, Range, the intermediate chamber is pressur- psi psi The Model DPV-1 Dry Pipe Valve is a ized and water flows through the alarm differential type valve that utilizes a port(Ref. Figure 36) at the rear of the 20 10 substantially lower system(air or nitro- DPV-1 Valve to actuate system water gen) pressure than the supply (water) flow alarms. The flow from the alarm 60 15-23 pressure, to maintain the set position port is also sufficient to close the oth- shown in Figure 3A. The differential erwise normally open Automatic Drain 80 20-28 nature of the DPV-1 is based on the Valve in the valve trim. area difference between the air seat After a valve actuation and upon sub 100 25-33 and the water seat in combination with P the ratio of the radial difference from sequent closing of a system main con- 120 30-38 the Hinge Pin to the center of the trol valve to stop water flow,the Clap- Water Seat and the Hinge Pin to the per Assembly will latch open as shown 145 35-43 center of the Air Seat. The difference in Figure 3D. Latching open of the is such that 1 psi (0,07 bar) of system DPV-1 will permit complete draining of 165 40-48 air pressure can hold approximately the system(including any loose scale) 5.5 psi(0,38 bar)of water supply pres- through the main drain port. 185 45-53 sure. During the valve resetting procedure 205 50-58 Table B establishes the minimum re- and after the system is completely quired system air pressure that in- drained; the external reset knob can 225 55-63 cludes a safety factor to help prevent be easily depressed to externally un- false operations that occur due to latch the Clapper Assembly as shown 250 60-68 water supply fluctuations. in Figure 3E. As such, the Clapper Assembly is returned to its normal set TABLE B The Intermediate Chamber, of the position to facilitate setting of the dry SYSTEM AIR PRESSURE DPV-1 is formed by the area between pipe sprinkler system, without having REQUIREMENTS the Air Seat and Water Seat as shown to remove the Handhole Cover. in Figure 313.The Intermediate Cham- ber normally remains at atmospheric pressure through the Alarm Port con- nection and the valve trim to the nor- mally open Automatic Drain Valve (Fig.4,5, or 6). Having the Intermedi- ate Chamber, Figure 313, open to at- mosphere is critical to the DPV-1 Valve remaining set,otherwise the full resulting pressure of the system air pressure on top of the Clapper Assem- bly cannot be realized. For example and assuming a water supply pressure of 100 psi(6,9 bar), if the system air pressure is 25 psi (1,7 bar) and there was 15 psi (1,0 bar) pressure trapped in the Intermediate Chamber, the resulting pressure across the top of the Clapper would only be 10 psi (0,7 bar).This pressure would be insufficient to hold the Clap- per Assembly closed against a water supply pressure of 100 psi (6,9 bar). It is for this reason that the plunger of the Automatic Drain Valve must be de- pressed during several of the resetting steps, as well as during inspections, making certain that the Automatic Drain Valve is open. When one or more automatic sprin- klers operate in response to a fire, air pressure within the system piping is relieved through the open sprinklers. When the air pressure is sufficiently reduced, the water pressure over- comes the differential holding the Clapper Assembly closed and the Clapper Assembly swings clear of the water seat, as shown in Figure 3C,