Norman Noe Co., Inc. - Opflow Article

A water tank acts as a relief valve on your water system. If the pressure in the system increases past its design capacity, it raises the water in the tank past the high-water level. The water then spills into the weir box or overflow pipe inside the tank, and the excess water drains out of the tank. This is usually a fail-safe system that stops excessive amounts of pressure from building up in the underground water lines.

On a single-tank water system, when the tank is taken out of service due to a tank freeze-up, inspection, or maintenance, it usually must be isolated from the system. Relief valves are placed on fire hydrants to "replace" the tank and relieve any excess water pressure. How these are installed can be critical to their success, and the number of valves to be installed and their positioning in the water system will vary from one system to another.

We can generally say that two relief valves are better than one. If only one valve is installed, problems can arise. A single valve can malfunction, it can be vandalized, or a good samaritan may mistake the blowoff of the valve for a problem and turn off the hydrant. These problems have occurred in the past, resulting in excessive pressure and leaks in the system.

A System That Works
The following system has worked for us in the past. First, do not make any changes in your system before you install the relief valves. Leave the pumps on. This is a key element. Then, the gate valve that isolates the water tank should be located and a turnkey installed. The relief valves are then installed on the fire hydrants, making sure that the location has good drainage for the blowoff water. Do not allow this water to endanger the public or property, such as wetting or icing down a sidewalk or street or flowing onto a garden.

If the relief valves have pressure gauges, don't put too much faith in them. Remove the end cap from the relief valve and loosen the lock out from the adjuster. Slowly open the fire hydrant all the way. Make sure the spring inside the relief valve isn't stuck by opening and closing this spring manually. This can be done easily with the end of a crescent wrench.

Now, adjust the pressure adjuster on the end of the valve from almost open to almost closed. Do this several times. This "exercises" the spring in the valve. By now you should be good and wet. Adjust the pressure adjuster to its closed position, shutting down the water flow. Now, slowly open the adjuster. You will first hear a hissing sound as air escapes the valve.

Continue opening the adjuster until the water just starts "spitting" out the valve. Stop at this point, tighten the lock nut on the pressure adjuster and replace the end cap. No matter what the pressure gauge on the valve says, the relief valve should now be set just a few pounds below the pressure of the hydrant.

Repeat this procedure with any other relief valves to be installed. Loosen the nuts of the tank's removable access head, and close the valve that isolates the tank from the water system. The water tank may now be drained from the tank's drain valve or drain hydrant. Again, observe proper drainage and public safety.

After the tank is drained, immediately remove the access head. Usually the pumps are then set on manual-hand. Pump only the minimum volume of water into the system that is required. The pressure in the system should be closely monitored, and the relief valves should be checked and adjusted if necessary. Now you can tell the clerk to put the telephone back on the hook.

Norman Noe is president of Norman Noe Co., a water tank inspection and consulting firm that also supplies relief valves. He has served on AWWA's Steel Tank Manual Task Force and is a NACE Level III international cerificated coatings inspector. Noe is a patron member and Lead Paint Bulletin sponsor of the Steel structure Painting Council, for which he also serves as a technical committee member of the Surface Preparation Group, Industrial Abrasive Blast Cleaning, Power Tool Cleaning, Inspection. He can be reached at (317) 933-2274.