Dry Pipe Valve
Model A-1, 4 Inch (DN100)
FlangexGroove
GENERAL DESCRIPTION
The Star 4 inch (DN100), Model A-1 Dry Pipe Valve is a
differential valve used to automatically control the flow of
water into a dry pipe fire protection sprinkler system upon
operation of one or more automatic sprinklers. The Model
A-1 Dry Pipe Valve also provides for actuation of fire
alarms upon system operation.
Dry pipe sprinkler systems are typically used in unheated
warehouses, parking garages, store windows, attic
spaces, loading docks, and other areas exposed to freez-
ing temperatures where water filled pipe cannot be util-
ized. When set for service, the dry pipe sprinkler system
is pressurized with air (nitrogen), and the loss of air pres-
sure through an operated automatic sprinkler, in re-
sponse to heat from a fire, permits the Model A-1 Dry
Pipe Valve to open and allow a flow of water into the sprin-
kler system piping.
The differential design of the Model A-1 Dry Pipe Valve is
such that the minimum air pressure in the piping is calcu-
lated to be approximately 1/5 of the static water supply
pressure plus an added safety factor that helps prevent a
false operation that might otherwise occur due to water
supply pressure fluctuations.
WARNING
The Model A-1 Dry Pipe Valve described herein must be
installed and maintained in compliance with this docu-
ment, as well as with the applicable standards of the Na-
tional Fire Protection Association, in addition to the stand-
ards of any other authorities having jurisdiction. Failure to
do so may impair the integrity of this device.
The owner is responsible for maintaining his fire protec-
tion system and devices in proper operating condition.
The installing contractor or sprinkler manufacturer should
be contacted relative to any questions.
TECHNICAL DATA
Approvals
UL and ULC Listed. FM and LPC Approved.
Working Water Pressure
20 to 175 psi (1.4 to 12.1 bar).
Friction Loss
Refer to Figure 3.
System Air Pressure Requirements
Refer to Table A.
Physical Characteristics
Body components illustrated in Figure 1 are constructed
of cast iron. The seat ring is copper, and the clapper is
ductile iron. The clapper facing is Buna-N.
OPERATION
The Model A-1 Dry Pipe Valves are differential type
valves that utilize a substantially lower system (air) pres-
sure than the supply (water) pressure to maintain the set
position shown in Figure 2-A. The differential nature of
the Model A-1 Dry Pipe Valve is based on the area differ-
ence between the air seat and the water seat. The differ-
ence is such that 1 psi (0.07 bar) of system air pressure
can hold approximately 5 psi (0.34 bar) of water supply
pressure.
The minimum system air pressure (Ref. Table A) is, there-
fore, calculated to be approximately 1/5 of the static water
supply pressure, plus a safety factor, to help prevent a
false operation that might otherwise occur due to water
supply pressure fluctuations.
Priming water within the body of the Model A-1 Dry Pipe
Valve, as shown in Figure 2-A, helps to maintain a tight
air seal at the air seat. Between the air and water seats,
an intermediate chamber is formed, and the intermediate
chamber is normally open to atmosphere through the
alarm port and piping to the Automatic Drain Valve
(5 - Fig. 4).
Having the intermediate chamber open to atmosphere is
critical to the Model A-1 Dry Pipe Valve remaining set,
otherwise the full resulting pressure of the system air
pressure on top of the Clapper Assembly cannot be real-
ized. For example, if the system air pressure is 40 psi
(2.7 bar) and there was 25 psi (1.7 bar) pressure
trapped in the intermediate chamber, the resulting pres-
sure across the top of the Clapper would be only 15 psi
(1.0 bar), which would be insufficient to hold the Clapper
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 needs to be depressed several
times during resetting of the Model A-1 Dry Pipe Valve,
414-570-5000 • 800-558-5236 • FAX 414-570-5010
2-00
2-2.1.31
STAR SPRINKLER INC.
www.starsprinkler.com
#1097 Valve
#1210 Trim
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