Web Exclusive! Faster Water Transit Times for Large Dry Pipe Fire Sprinkler Systems
Predicting water transit times for fire sprinkler systems controlled by conventional differential dry pipe valves has long been the nemesis of the design technician. Section 4-2.3.1 of the 1999 edition of NFPA 13 states that not more than 750 gallons (2,839 L) of system capacity shall be controlled by one dry pipe valve. The "exception" to this limitation allows the system piping volume to exceed 750 gallons (2,839 L) provided that the system design is such that water is discharged from the inspector's test connection in not more than 60 seconds. This exception gives contractors the opportunity to test the limits of their design creativity and nerve.
A new dry pipe system called the LDX system from The Reliable Automatic Sprinkler Company was designed to lower system air pressures. LDX stands for Lo-Pressure Dry system with an external reset. Lower system operating air pressures provide the contractor with the opportunity to install larger dry pipe systems with faster water transit times.