Dry Pipe Valves and Air Check Valves

Air check valves are special, small, dry pipe valves that are usually connected to a wet pipe system. The alarms are actuated at the wet pipe system riser when the air check valve "trips." To prevent premature operation, the valves should be fitted with an air chamber to maintain at least 50 gallons of air in the chamber and on the system.

Perform the 2-inch drain test quarterly by opening the 2-inch drain valve fully and recording the pressure at the lowest point. Close the 2-inch drain valve and record the pressure at the stabilization point. Notice whether pressure returns quickly or slowly. Maintain a continuous record of drain tests.

If the recorded pressure when the valve is wide open is similar to previous recordings and pressure returns quickly, it is normal.

If recorded pressure when the valve is wide open is significantly lower or pressure is slow to return when the valve is closed, there may be an obstruction in the waterway. Check for partially closed valves to the sprinkler system.

Because dry pipe sprinkler systems are installed in areas where temperatures are expected to drop below freezing, all parts of the system must be airtight and kept free of water. Complete drainage is essential.

Each fall, before freezing season comes, check the pitch of all piping carefully using a spurt level to detect dips and small pockets in the lines. Check for broken, loose, or missing hangers; and water in low point drains.

Check air and water pressures weekly. If air pressure losses exceed 10 psi, check the entire system for tightness and eliminate air leaks. Principal checking methods are as follows:

. Put a strong smelling oil, such as oil of peppermint, into the air supply. This will produce a strong odor at the point of leakage.

. Paint fittings with a soapy water solution and watch for bubbles.

Check the temperature of valve enclosure and maintain a temperature above 42F.

Make certain that the valve between the intermediate chamber and the alarm devices is open on dry pipe valves.

Check drip valves at intermediate chambers, making certain that clappers or balls are in a position to allow drainage. This is done by lifting push rods or by inserting a pencil in the opening. Water leakage through this valve is an indication that the water clapper is not holding tightly to the seat.

Check the air pressure. The air pressure versus water pressure for differential dry pipe valves should be as outlined in table 8-3 unless otherwise specified by the manufacturer's operating instructions. Certain mechanical dry pipe valves are designed to trip at a fixed pressure of 10 to 15 psi. Maintain 30 psi air pressure on these valves.

Basic inspections for accelerators and exhausters include the following: . Check air pressure. The system and the quick-opening device air pressure should be the same. . Relieve excess pressure in the quickopening device by opening bleeder valves or loosening air gauges.

If the system pressure is high, relieve the excess pressure through the priming water test valve. Close the valve as soon as pressures balance. To avoid the possibility of tripping the dry pipe valve, do not open the priming test valve more than one turn and keep the valve to the quick-opening device closed while the priming test valve is open.

To make sure that dry pipe valves will operate effectively in fire situations, they should be trip-tested annually as follows:

1. Close the main control valve.

2. Open the 2-inch drain.

3. Open the main control valve until 5 psi pressure shows on the water gauge.

4. Close the 2-inch drain valve slowly.

5. Open the inspector's test connection of the system. Where there is no test connection, use the most remote low point drain.

6. As soon as the dry pipe valve trips, close the main control valve and open the 2-inch drain. This is particularly important in permanently cold areas.

7. Record initial air and water pressures, air pressure at the trip point, and time required for tripping.

8. Examine and clean the dry pipe valve interior. Replace facings and gaskets if needed.

9. Reset the dry pipe valve and the open control valve.

10. When a dry pipe valve fails to trip or when a clapper fails to latch in the open position, notify the person responsible for fire protection so that a qualified sprinkler contractor may be contacted.

To test dry pipe valves you should do the following:

1. Close the main control valve and open the 2-inch drain valve and low point drain valves.

Table 8-3.-Differential Dry Pipe Valve Air Pressure Specifications

Close low point drain valves when water stops flowing.

2. Clean clapper facings and seats.

3. Clean the valve interior.

4. Place clappers on seats and make certain the antiwater column latch is in place. Bolt on the cover. Do not use grease or other material to help seat clappers. Fill the system with 10 psi air pressure to blow out any residual water through low point drains.

5. Open valves at the top and bottom of the priming chamber and priming test valves.

6. Admit water to the priming chamber until water flows out of the test valve. Close this valve.

7. Close the priming chamber valves.

8. Admit air pressure to the system.

9. Open the main control valve slowly.

10. Close the main 2-inch drain valve, except where water hammer conditions exist. In this case, leave the 2-inch drain valve open until pressures stabilize.

To check air supply piping, do the following:

Note air pressure within 12 to 24 hours after resetting the dry pipe valve. If air leakage exists, test sprinkler piping for leaks.

Make sure the valves to manually operated compressors are tightly closed. A slow air leak back through one of these valves can trip the dry pipe valve.

Examine restriction orifices in air piping and air pressure regulators, if used, from automatic air compressors to dry pipe valves.

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