> Dry System
A dry system is a fire protection system which is filled with air. The air is under pressure. The components of a dry system are the same as a wet system except a dry valve is required. A dry valve is a specially designed valve which uses a mechanical apparatus or straight differential to hold a higher water pressure from overcoming a lesser air pressure in the system. Most dry systems should not have air pressure greater than 40 psi. It can be seen that both system size and static air pressure are important in obtaining a satisfactory trip test. Where a dry system is large and it exceeds 500gpm in capacity a miniature dry valve, when tripped, city water is piped directly into the intermediate chamber forcing the clapper open. This event speeds the delivery of water to the open head or test valve. Also see Standpipe System for additional information.

Main Points to Establish

Main Control Valve
* Is the main control valve open and all valves down stream of the connection to the water supply open?
* Is this and all other valves controlling water to the system locked in the open position or supervised and functioning?

Pressure Gauges
* There should be at least two on a dry system one indicating the city water pressure and one indicating the air pressure. In most cases they should read different amounts, and the air normally less than the water pressure. Where there is a quick opening device it also has a gauge and should read the same pressure as the air pressure in the system.

Alarm Mechanism
* On a dry system a water motor gong piped from the dry valve or a pressure switch attached to a local bell is standard.

Drain
* This valve allows the system to be drained and is used to test to see if the city water valve is open. This is done by opening the valve wide open while reviewing the pressure drop on the pressure gauge. The loss should not be significant. If it is the city water supply should be investigated.

Fire Department Connection
* This is used to allow the fire department to pump into, using their pumper truck to supplement the city water pressure. Threads should be checked to see if they meet standard threads used by local fire department.
* The siamese connection has to be piped in between the control valve and the dry pipe valve.

Alarm Testing Apparatus
* This is usually a 1" located somewhere in the building and piped to the outside or a drain capable of sustaining a full 1" flow equivalent of one sprinkler orifice. When this valve is opened the alarm must ring.

Air Compressor
* Each dry system must have an approved air source which is capable of replenishing the air within 45 minutes and must be U.L. approved of this application.

Air Maintenance Device
* This is an approved device which allows air to flow into the system at a rate approved by the NFPA standards. It is not installed on all systems as it is a contractor option.

Sprinklers
* All sprinklers in the pendent position must be approved dry type sprinklers. If the area where pendent sprinklers are installed is heated, the sprinklers can be ran using a return bend, thus eliminating the dry pendent sprinklers. All changes in piping directions which caused a trapped portion of piping must be provided with the appropriate drain or drum drip assembly.
* There should be a supply of extra sprinklers in the facility as per NFPA #13 and a sprinkler wrench.
* As you walk through a facility there should be no gaps in coverage in those areas requiring sprinklers.
* The question should be asked if any area has been changed from one occupancy to another after original system had been installed.
* What is the age of the sprinklers?

Certification of Inspection
* The owner, under NFPA #13A, is responsible for certain tests and the collection of certain data to demonstrate the performance capability of the system. The owner should have documentation of periodic testing and inspection.

 

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