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Pressure testing is the most fundamental test for valves. Each valve must undergo a pressure test before leaving the factory. Currently, the domestic standards for pressure testing of valves are GB/T13927-1992 \"General Valves – Pressure Testing\" and JB/T 9092-1999 \"Inspection and Testing of Valves\". GB/T13927-1992 was formulated with reference to the international standard ISO5208-1991 \"Pressure testing of industrial valves\", while JB/T 9092-1999 was formulated with reference to the American Petroleum Institute standard API598-1996 \"Inspection and testing of valves\". GB/T13927-1992 mainly specifies the pressure testing for gate valves, globe valves, check valves, plug valves, ball valves, butterfly valves, diaphragm valves, etc. The JB/T 9092-1999 standard is applicable to the pressure testing of gate valves, globe valves, plug valves, ball valves, check valves, and butterfly valves with non-metallic or metallic seals for the closing elements. Other types of valves can also undergo pressure testing in accordance with these two standards, as specified by the product standards. Currently, steel valves are generally subjected to pressure testing in accordance with the JB/T 9092-1999 standard. Iron and copper valves, as well as the forgings and castings of valves, are subjected to pressure testing in accordance with GB/T13927-1992. At present, valves, forgings, and castings covered by the following standards are subjected to pressure testing in accordance with the GB/T13927-1992 standard. In the GB/T13927-1992 and ISO5208-1991 standards, the pressure testing of valves includes: housing testing ； Upper seal test (ISO5208-1991) (this test item is not available) ； Sealing test. Although the GB/T13927-1992 and ISO5208-1991 standards do not explicitly classify seal tests into low-pressure seal tests and high-pressure seal tests. However, within a certain range of nominal diameter and nominal pressure, low-pressure sealing tests can be carried out using gaseous media, while high-pressure sealing tests can be conducted using liquid media across the entire range of nominal diameter and nominal pressure. GB/T13927-1992 and ISO5208-1991 stipulate that for smaller nominal diameters (DN≤50) and nominal pressures (PN≤0.5MPA), it is permissible to use a gas medium at a pressure of 0.5-0.7MPA for the shell test. JB/T 9092-1999 and API598-1996, on the other hand, specify that a pressure equal to 1.5 times the nominal pressure should be used for shell testing. Furthermore, there are also significant differences between the requirements of GB/T13927-1992 and ISO5208-1991 regarding the minimum test duration and the allowable leakage amount. ISO5208-1991 and API598-1996 are the currently authoritative international standards for valve pressure testing, and many countries formulate their own standards by referring to these two standards. Below, the main standards for pressure testing at home and abroad are listed and compared according to the categories of pressure testing items. Section 1: Shell Testing of Valves The shell testing of valves involves performing a pressure test on the entire valve housing, which is composed of the valve body, the valve cover, and other connected components. Its purpose is to test the tightness of the valve body and valve cover, as well as the pressure resistance of the entire housing, including the joint between the valve body and valve cover. Each valve shall undergo a shell test before leaving the factory. Before the shell test, it is not allowed to paint the valve or apply any other anti-leakage coatings. However, chemical rust prevention treatments that do not provide sealing are allowed, as well as lining valves. If the user inspects the inventory valves randomly, the existing coating will no longer be removed. During the testing process, no external forces that could affect the test results shall be applied to the valve. The test pressure should remain constant during pressure holding and testing. When conducting tests with liquids, gas within the valve cavity should be removed as much as possible. After the holding time has elapsed, the housing (including the stuffing box and the joints between the valve body and the valve cover) must not leak or suffer any structural damage. Methods and steps for shell testing: Close the inlet and outlet valves, tighten the packing gland, and place the operating element in a partially open position ； Fill the donor cavity with the test medium and gradually increase the pressure to the test pressure (check valves should be pressurized from the inlet side) ； After the specified time has passed, check the housing (including the stuffing box and the joints between the valve body and the valve cover) for any leaks. Test temperature, test medium, test pressure, minimum test duration, and allowable leakage rate for shell tests. Section 2: Upper Sealing Test of Valves The upper sealing test is a test to evaluate the sealing performance of the seal between the valve stem and the valve cover. Gate valves and globe valves that require upper sealing performance must undergo an upper sealing test. Methods and steps for the upper seal test: Seal the valve’s inlet and outlet, loosen the packing gland (if the valve is equipped with a device for checking the upper seal, and its performance can be reliably tested without loosening the packing gland, then there is no need to do so). With the valve in the fully open position, close the upper seal, fill the chamber with the testing medium, and gradually increase the pressure to the specified test pressure; thereafter, check the performance of the upper seal. This test can be conducted before the shell test. Test temperature, test medium, test pressure, minimum test duration, and allowable leakage rate for the upper seal test. Section 3: Sealing Test of Valves The sealing test is a test to evaluate the sealing performance of the moving parts and the sealing surfaces of the valve body. Before the sealing test, oil stains on the sealing surface should be removed, but a thin layer of a protective agent with a viscosity not greater than that of kerosene is allowed to be applied ； Valves sealed with grease allow the application of the grease specified in the design requirements. During the test, the valve should not be subjected to any external forces that could affect the test results. The valve should be closed in the manner specified by the design. The sealing test should be conducted after the housing test. The pressurization method for the sealing tests of main valves is specified according to regulations. However, for valves that specify the flow direction of the medium, pressure should be applied in accordance with the specified flow direction (except for check valves). During testing, pressure should be increased gradually to the specified test pressure, after which the sealing performance of the sealing pair is checked. Standards such as API 1598-199 and JB/T9092-1999 classify seal tests into high-pressure seal tests and low-pressure seal tests, and specify that butterfly valves shall undergo high-pressure seal tests. Other types of valves must be able to withstand high-pressure sealing tests, but this test is usually not carried out. For check valves, a high-pressure sealing test or a low-pressure sealing test can be conducted. Standards such as ISO5208-1993 and GB/T13927-1992 do not explicitly classify seal testing into high-pressure testing and low-pressure testing. The test medium is selected at the discretion of the manufacturer. However, when using gas as the test medium, the test should be conducted at low pressure ； When a liquid is used as the test medium, tests can be conducted at high pressure.