These limits are established by the appliance manufacturer or your company policy. You can tell the regulator has shut off the flow of propane when the pressure stops increasing. There are some important facts to keep in mind when conducting these tests: 1. A pressure test is normally conducted with a minimum test pressure of 1 ½ times above the normal operating pressure of the piping. 2. Interruption of service is when the vapor pressure in the vapor distribution system is no longer sufficient to allow the appliances to operate. Many times this is discovered as an “out of gas” call. Appliances with 100% safety shut-off valves An appliance with a 100% safety shut-off valve will automatically stop any gas from passing through the gas control to the appliance combustion chamber when the control is in the “ON” position and there is no ignition source. When performing a leak check on systems with this type of appliance, you must ensure two valves are in the “ON” position: • The 100% safety shut-off valve • The manual gas shut-off or “gas cock” This allows propane to flow through the system to the 100% safety shut-off valve to ensure that the valve is not allowing any propane to the appliance chamber, thereby proving its functional stability. In other words, the valve is not allowing gas to pass through, often called a “passing gas valve.” A valve that is passing would have to be replaced as it is unsafe and not shutting off on safety. Appliances without 100% safety shut-off valves An appliance without a 100% safety shut-off valve does not have a safety device to automatically stop gas from passing to the combustion chamber. When performing a leak check on this type of appliance, the manual shut-off valve must be in the “OFF” position; this will completely shut off the supply of gas to the appliance. The words “shutting off” are for gas ranges and other appliances with a standing pilot (one that runs 24/7). You can shut off the gas to those pilots by finding the shut offs on the equipment, on ranges that include the broiler and oven pilots. Keep in mind you will not be testing anything downstream from those shut offs, so they will need to be tested with a leak detection solution. Figure 3. The U-shaped tube manometer and pressures Using a Manometer A manometer (Figure 3) is a gauging device used to measure gas pressure at low levels, such as interior piping inside a residence. Piping systems that supply appliances with gas at pressures of ½ per square inch gauge (psig) or less may be leak checked by inserting a manometer downstream of the final-stage regulator. In this test all of the regulators in the system must be open and unlocked. A water manometer may be connected to a regulator outlet test tap, to a special test adapter downstream from the appliance shut off valve or directly to the inlet of an appliance gas control test tap. Be certain the manometer is filled with water according to manufacturer’s instructions and is set to zero reading before testing. You can also use an electronic manometer (See Figure 2), which works on the same principle as a water manometer, but gives a digital reading instead of a water level reading. WARNING Do not use a water manometer on modulating condensing equipment or any equipment using a negative pressure gas valve. Those systems will suck the water out of the manometer into the gas valve, rendering the valve useless. You can also use a magnehelic gauge (see Figure 4), or a 0 to 35" water column (w.c.) pressure gauge kit, which gives a dial reading. Any gas pressure measuring device should be properly calibrated according to manufacturer’s instructions. Using a Vapor Meter for Testing A vapor meter may also be used to perform a leak check. Immediately prior to performing the leak check make sure the meter is in good operating condition. Watch the meter small test dial (see Figure 5 and Figure 6) with a small amount of gas being used and see if it moves; if it does not, replace the meter and have the one removed repaired. Also check for any structural damage to the meter and regulator, along with the piping system. Figure 4. Magnehelic Gauge ICM/May/June 2016 21
ICM May-June 2016
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