TELLTALE SIGNS OF WATER HEATER GAS CONTROL VALVE OVERPRESSURIZATION

摘要

Regulators and gas control valves are at the heart of gas pressure regulation. The regulators are designed to limit the pressure delivered to the gas control valves to a specified maximum, typically 1.7 kPa (7 inches water column gauge (w.c.)) for natural gas and 3.2 kPa (13 inches w.c.) for propane. The gas control valve allows gas to flow to its associated appliance burner when there is a call for operation. The gas control valve usually has internal regulation, which reduces the manifold pressure below that of the incoming pressure, typically about 0.87 kPa (3.5 inches w.c.) for natural gas and 2.5 kPa (10 inches w.c.) for propane. Although fires, flash fires and explosions can occur if gas systems and appliances are subjected to significantly higher than normal pressures, overpressurization is too often incorrectly identified as the cause of these types of incidents. When it does occur, evidence of overpressurization can be obvious, such as a failed regulator or a heat pattern above the water heater gas control valve. Other times, however, the physical evidence observed directly contradicts this conclusion - regulators operate correctly, control valve or gas system is leak free, and no visible signs of an overpressure. A study was conducted on the most common Robertshaw water heater gas control valves, both old and new. Testing was done to determine 1.) whether or not one can expect to find telltale signs of overpressurization and what the telltale signs are for a particular control valve, 2.) what pressures and pressurization scenarios are required to cause leakage, and 3.) what leak rates are created by overpressurization events.