ASME Pressure Relief Valve Testing
Many processes involve the use of high pressure steam, water or air. Piping systems carrying these fluids must be protected from over-pressures that could cause damage or injury. A pressure relief valve is a device that opens to vent any pressure higher than the relief valve’s operating set point. The water heater in your house, for example, has a pressure relief valve set to open at a pressure that is lower than the burst pressure of the heater tank. That way if pressure inside the tank exceeds the relief valve’s set point pressure, the valve will open and vent the pressure before the tank is damaged – you get a wet floor but you don’t have to replace the heater tank.
Pressure relief valves come in all sizes and pressures and these are critical parts of a high pressure piping system carrying steam in an industrial plants, refineries, power plants, etc. The ASME has established criteria for the size and set point pressures for relief valves operating in industrial systems. Additionally, these valve are tested on a regular basis to insure that they open at the correct pressure and do not impede the flow of fluid as the pressure is vented. The vales are tested at their operating pressures and temperatures, and the opening pressure and pressure drop through the valve as it vents must be measured.
There are testing laboratories that are used to test industrial pressure relief valves by simulating the operating conditions for water, air and steam. One customer of Validyne has a test lab capable of generating up to 10,000 lbs. per hour of steam at 300 psig, air flows to 3500 SCFM at 500 psig and water flow rates of 500 gpm at 300 psig. Pressure relief valves are tested depending on their operating conditions, and the valves are instrumented to verify correct operation at their set point pressure.
The Validyne product used to make relief valve measurements is the DP15 pressure transducers. One transducer is used to measure the pressure upstream of the relief valve, a second DP15 measures the downstream pressure. These transducers are 300 or 500 psi, depending on the test. A third DP15 measures the pressure drop across the relief valve when it is flowing and this transducer is typically 100 In H2O full scale. The DP15s are used because they can be mounted remotely from the control station. A large steam relief valve, for example, is connected to piping with runs of 25 and 30 feet. The DP15 can be mounted at the measurement point and the cable to the demodulator can be up to 50 feet with no compromise in calibration.
The pressure transducers are connected to Validyne CD23 demodulator with digital display. The CD23 features large LED displays that are helpful for the operator to see while opening and closing large control valves during the test. The display can be given directly in PSIG and the CD23 provides an analog output proportional to pressure that can be connected to a LabVIEW computer to record the pressures during the test. Alternatively the pressure sensors can also be connected to the USB2250 DAQ.
The Validyne CD23s and DP15s have given many years of service in this difficult environment and this reliability, plus the ability to interface to a data acquisition system make it a great solution for relief valve testing.
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