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The testing of pressure relief valves includes housing testing and performance testing. Symbols, units, and definitions of the relevant performance parameters of pressure relief valves. Section 1: Shell testing of pressure relief valves. The testing medium for pressure relief valve shells is normal temperature water. The test pressure is 1.5 times the nominal pressure. Section 2: Performance Testing of Pressure Relief Valves 1. General Requirements for Testing The testing objectives, location, testing medium, measurement methods, as well as the testing instruments and equipment should, as much as possible, correspond to the actual operating conditions of the product, so as to accurately reflect its performance. Before the experiment, consultations should be held with the relevant parties to reach an agreement. The supervising tester should have practical experience in flow measurement and be present throughout the testing process. The test shall result in a test report prepared in accordance with the standards, and it shall become valid only after being signed by the person supervising the test and stamped by the relevant authority. No adjustments should be made to the valve during the test. When the test conditions change, adjustments can be made again, but the parts must not be replaced. The test pipe should be the same as the channel of the valve being tested. 2. Testing instruments 1) Pressure gauges can be liquid pressure meters and Bourdon tube pressure gauges; other pressure measuring instruments can also be used. The error of the pressure measuring instrument should be less than or equal to 0.5% of the instrument’s range, and the pressure value being measured should fall within the 30%-70% range of the instrument’s range. 2) Thermometers can be glass liquid thermometers or other temperature measurement instruments (such as thermocouples and thermal resistance thermometers, etc.). Except that glass liquid thermometers must be inserted into a sleeve before being installed in the pipeline, the other temperature sensing elements mentioned above can either be inserted into a sleeve or installed directly in the pipeline. The thermometer bulb should be clean and free of rust, and it should be filled with an appropriate liquid whose boiling point is higher than the highest temperature to be measured. 3) The flow meter can be a flow meter or a calibrated standard throttling device. Sufficiently long straight pipe sections should be provided before and after the throttling device; alternatively, a direct measurement method involving the collection and weighing of the discharged medium or its condensate can be used. Before conducting the continuous operation test, the instruments (including sensors, strain gauges, counters, pressure gauges, etc.) shall be calibrated as required. The accuracy of the pressure gauge must be at least grade 1.5. 3. Test Methods (1) Sealing performance test method 1) Test medium: Ambient air ； Water (suitable for water pressure reducing valves) ； Steam. 2) The test pressure shall be the highest inlet operating pressure (numerically equal to the nominal pressure) and the lowest inlet operating pressure. 3) Test procedure: For soft-seal structures, during the static sealing test, the pressure reducing valve is closed (the adjustment spring is in its free state). The maximum operating pressure is applied at the inlet, while the outlet is connected to the atmosphere. The leakage rate is measured and recorded, and the average of the two measurements is taken. Gas leak detection method, using a leak induction tube for measurement. The inner diameter of the introduction tube is 6 mm, its length is not more than 500 mm, and its height above the liquid level in the tank is not more than 300 mm; the leakage rate is recorded after applying pressure for 5 minutes. For metal-sealed structures, the pressure relief valve is closed during static sealing tests (the adjustment spring is in its natural state). The maximum operating pressure is applied at the inlet, while the outlet is connected to the atmosphere, in order to determine the leakage rate at the outlet. When it is not convenient to measure the leakage rate, dynamic sealing tests are permitted. At this point, the pressure relief valve closes (the adjusting spring is in its relaxed state); the highest operating pressure is applied at the inlet, while the outlet pressure is set to either the highest possible outlet pressure or the lowest possible outlet pressure. Then, close the stop valve after the pressure relief valve, and measure and record the pressure increase value using the outlet pressure gauge. (2) Voltage regulation test method: Voltage regulation test system. Test procedure: The pressure relief valve is closed (the adjusting spring is in its free state). Open the shut-off valve behind the pressure regulator, set the inlet pressure to the maximum operating pressure, and slowly adjust the adjustment screw (or handwheel) of the pressure regulator so that the outlet pressure varies continuously between the maximum and minimum values set by the spring of that pressure stage. Repeat this two times; each time a gear is adjusted, the pointer of the outlet pressure gauge must be returned to zero. Otherwise, adjust the opening degree of the shut-off valve again and record the observed conditions. (3) Flow rate testing method 1) Determination of the flow capacity C value: With a pressure difference of 0.1 MPa before and after the pressure reducing valve, and a fluid density of 1 g/cm3, the flow rate through the valve per hour at full opening (in m3/h or t/h) is the K value. The relationship between the flow capacity C and K is as follows: C=1.17K. The test medium is water at 5–30°C. During the test, the pressure on the inlet side was maintained at 0.1 MPa, while the outlet side was connected to the atmosphere, thereby maximizing the opening degree of the pressure relief valve. The container weighing method or a flow meter is used to measure the flow rate, and the arithmetic average of the values obtained from 3 measurements is taken. 2) Determination of maximum flow rate: Test procedure: Specify the highest inlet operating pressure. Adjust the pressure reducing valve to a certain outlet pressure. At this point, the shut-off valve downstream of the pressure relief valve results in a minimal flow rate (i.e., the outlet pressure returns to zero). Then, gradually open the shut-off valve to bring the outlet pressure deviation to the maximum allowable value. The flow rate measured at this point is the maximum flow rate. (4) Test method for flow characteristics Test system for flow characteristics Test procedure: Specify the maximum inlet operating pressure. Adjust the pressure reducing valve to a certain outlet pressure. At the same time, adjust the stop valve behind the pressure reducing valve so that the outlet flow rate is 20% of the maximum flow rate under those operating conditions. Then, gradually open the shut-off valve to bring the outlet flow to 100% of the maximum flow rate for that operating condition. Record the deviation value of the outlet pressure at this time. (5) Pressure characteristic test method, Pressure characteristic test system, Test procedure: Specify the maximum inlet operating pressure. The adjusted inlet pressures are the highest and lowest pressures within that spring pressure range, respectively. Maintain the maximum flow rate under this operating condition. Then, adjust the opening degree of the shut-off valve before the pressure reducing valve to vary the inlet pressure within the range of 85% to 105% of the maximum operating pressure, and record the deviation value of the outlet pressure at that time. (6) Test method for continuous operation test 1) Test requirements: Use clean tap water as the test medium. One cycle of turning on and off constitutes one test run. During testing of the pressure relief valve, each opening and closing of the valve following it corresponds to one opening and closing of the pressure relief valve. The opening degree of the pressure relief valve is determined by the inlet and outlet pressures set during testing, as well as the number of times per minute the control valve at the outlet opens and closes. As long as the test pressure is maintained, the dimensions of the test pipeline and the pressure reducing valve channel need not be identical; it is permissible to install converging (diverging) tubes before and after the straight pipe. The test can be terminated if either of the following conditions occurs: ① Direct flow, with equal pressure at the inlet and outlet ； ② Spring breakage ； ③ Diaphragm failure ； ④ Normal testing cannot be carried out due to damage to other components. 2) Test system. The test can be carried out once the valve under test passes the factory tests. Test procedure: Apply the maximum operating pressure on the inlet side, open the solenoid valve, slightly open the shut-off valve behind the pressure regulator (until the pressure gauge reads zero), and adjust the pressure regulator to achieve the desired outlet pressure. At the same time, make the solenoid valve open and close at the required frequency, and record the time and number of times. 4. Performance requirements (1) Sealing performance requirements: 1) For soft-sealing structures, the maximum allowable leakage amount during static sealing tests; 2) For metal-sealing structures, the maximum allowable leakage amount during static sealing tests is 0.5% of the maximum flow rate (the maximum flow rate is specified by each manufacturer). 3) During the dynamic sealing test of the soft-seal structure, the increase in the outlet pressure gauge reading should be zero. 4) During the dynamic sealing test of the metal-sealed structure, the increase in pressure on the outlet pressure gauge shall not exceed 0.2 MPa/min. (2) Pressure regulation performance requirements: Within the given range of spring pressure levels, the outlet pressure must be able to be adjusted continuously between its maximum and minimum values, without any sticking or abnormal vibrations. (3) Flow characteristic requirement: When the outlet flow changes, the negative deviation of the outlet pressure shall not exceed 20% for directly-acting pressure regulators ； For pilot-operated pressure relief valves, it is not more than 10%. (4) Pressure characteristic requirement: When the inlet pressure changes, the deviation in outlet pressure shall be no more than 10% for directly-acting pressure regulators ； For pilot-operated pressure relief valves, it is not more than 5%. (5) Continuous operation requirements: Number of overall tests. After a one-time test, the pressure relief valve shall still meet the performance requirements in terms of its sealing performance, pressure regulation performance, pressure characteristics, and flow characteristics. 5. Test report: Pressure relief valve test report.