What are the common media used for valve pressure testing? The pressure testing methods for industrial valves, including pneumatic valves, are as follows

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This post was last edited by At the foot of Hengshan Slope on 2018-5-22 07:10. In chemical production, valves are used wherever there is fluid flow; their importance in the chemical industry is self-evident. So today, YiKong Jun will discuss with everyone the pressure testing methods and precautions for commonly used valves. 　　Common media used for valve pressure testing include water, oil, air, steam, nitrogen, etc. The methods for pressure testing various industrial valves, including pneumatic valves, are as follows: 1. Globe valves and throttle valves – For strength testing of globe valves and throttle valves, the assembled valves are placed on a testing frame, the valve discs are opened, and the medium is injected to the specified level; then it is checked whether there is any sweating or leakage from the valve body and cover. Strength testing can also be conducted on individual pieces. The seal integrity test is only performed on globe valves. During the test, the stem of the stop valve is kept in a vertical position, the valve disc is opened, and the medium is introduced from the end below the valve disc to the specified level; the gaskets and seals are checked at this point. Once everything is satisfactory, the valve disc is closed and the other end is opened to check for any leaks. If both strength and sealing tests are to be conducted on the valve, the strength test can be carried out first; thereafter, the pressure is reduced to the value specified for the sealing test, and the packing and gaskets are inspected. Next, the valve disc is closed and the outlet end is opened to check whether there is any leakage at the sealing surfaces. 　　2 Gate Valve The strength test for gate valves is the same as that for globe valves. There are two methods for the sealing test of gate valves. 　　①The gate is opened to raise the pressure inside the valve to the specified value; then the gate is closed, and the gate valve is immediately removed to check for any leaks at the seals on both sides of the gate. Alternatively, a test medium can be injected into the plug on the valve cover until the specified pressure is reached, in order to check the seals on both sides of the gate. The above method is called intermediate pressure testing. This method is not suitable for conducting seal tests on gate valves with a nominal diameter of DN32 mm or less. 　　②Another method is to open the gate valve to raise the test pressure of the valve to the specified value; then close the gate valve and open one of the blind flanges to check whether there is any leakage at the sealing surface. Tilt the head back again and repeat the above test until it passes. 　　The sealing test at the packing and gasket of the pneumatic gate valve should be carried out before the seal test of the gate plate. 　　3 Ball valve The strength test of pneumatic ball valves shall be conducted with the ball in a partially open position. 　　①Sealing test for floating ball valves: Place the valve in a semi-open position, introduce the testing medium at one end while keeping the other end closed; rotate the ball several times, then open the closed end while the valve is in the closed state to check for any leaks. At the same time, examine the sealing performance at the packing and gasket areas to ensure that there are no leaks. Then, the test medium is introduced from the other end, and the above experiment is repeated. 　　②Sealing test for fixed ball valves: Before the test, rotate the ball several times with no load applied, with the fixed ball valve in the closed position. Introduce the test medium from one end until the specified pressure is reached; use a pressure gauge to check the sealing performance at the inlet side, using a pressure gauge with an accuracy of 0.5–1 grade and a range that is 1.6 times the test pressure. If there is no drop in pressure within the specified time, it is considered acceptable; then the test medium is introduced from the other end, and the above test is repeated. Then, set the valve in a semi-open position with both ends sealed, fill the internal cavity with the medium, and under the test pressure, check the packing and gaskets to ensure there is no leakage. 　　③The three-way ball valve should be tested for sealing performance at various positions. 　　4 Plug Valve ① When conducting a strength test on the plug valve, the medium is introduced from one end, with the remaining pathways sealed off. The plug is then rotated to each fully open operating position one after another for testing; the valve is considered qualified if no leakage is detected in the valve body. 　　②During the tightness test, for straight-through stopcocks, the pressure inside the chamber must be kept equal to that in the passageway. Rotate the plug to the closed position and perform inspections from the other end; then rotate the plug 180° and repeat the test. For three-way or four-way stopcock valves, the pressure inside the chamber must be kept equal to that at one end of the passageway. Rotate the plug sequentially to the closed position; introduce pressure from the perpendicular end while conducting inspections from the other ends simultaneously. 　　A layer of non-acidic light lubricating oil may be applied to the sealing surface on the plug valve test bench; it is considered satisfactory if no leakage or expanding droplets are observed within the specified time. The test time for plug valves can be shorter; it is generally specified as 1–3 minutes based on the nominal diameter. 　　Gas control valves shall be subjected to an air tightness test at 1.25 times the operating pressure. 　　5 Butterfly Valve The strength test for pneumatic butterfly valves is the same as that for globe valves. For the seal performance test of butterfly valves, the test medium should be introduced from the inlet side; the butterfly disc must be open while the other end is sealed, and pressure should be applied up to the specified value. After verifying that there are no leaks at the packing and other sealing points, the butterfly disc is closed and the other end is opened. The test is considered successful if no leaks are observed at the sealing surface of the butterfly disc. Butterfly valves used for flow regulation do not need to undergo sealing performance tests. 　　6 Diaphragm Valve: For the strength test of the diaphragm valve, the medium is introduced from either end; the valve disc is opened while the other end is kept closed. Once the test pressure reaches the specified value, it is considered successful if there is no leakage in the valve body or cover. Then reduce the pressure to the sealing test pressure, close the valve disc, and open the other end for inspection; no leakage indicates success. 　　7 Check Valve Test condition for check valves: For lift-type check valves, the axis of the valve disc is in a position perpendicular to the horizontal; for swing-type check valves, the axis of the flow channel and the axis of the valve disc are in a position approximately parallel to the horizontal line. 　　During the strength test, the test medium is introduced from the inlet side to the specified level, while the other end is sealed; the test is considered successful if there is no leakage from the valve body or the valve cover. 　　For the sealing test, the test medium is introduced at the outlet end, and compliance is achieved if no leakage is detected at the sealing surfaces, as well as at the packing and gaskets, at the inlet end. 　　8 Safety valve ① The strength test of the safety valve, like that of other valves, is carried out using water. When testing the lower part of the valve body, pressure is applied from the inlet I=I end, with the sealing surfaces closed; when testing the upper part of the valve body and the valve cover, pressure is applied from the outlet El end, with the other ends closed. It is considered qualified if there is no leakage from the valve body and valve cover within the specified time. 　　②For tightness tests and set-pressure tests, the commonly used test media are as follows: for safety valves used with steam, saturated steam is used as the test medium; for valves used with ammonia or other gases, air is used as the test medium; for valves used with water and other non-corrosive liquids, water is used as the test medium. For safety valves in some critical locations, nitrogen is commonly used as the testing medium. 　　The seal test is conducted using the nominal pressure value as the test pressure; it must be performed at least twice. It is considered successful if no leakage occurs within the specified time period. There are two methods for checking for leaks: The first is to seal all the connections of the safety valve, and then use butter to attach a piece of thin paper to the outlet flange; if the paper bulges, there is a leak, while if it does not bulge, the valve is intact. The second method involves using butter to attach a piece of thin plastic sheet or another type of sheet to the bottom of the outlet flange, filling the space with water to cover the valve disc; if no bubbles appear in the water, the valve is considered to be leak-free. The safety valve shall undergo pressure setting and reset pressure tests no less than 3 times; it is considered qualified if it meets the specified requirements. 　　9 Pressure relief valve ① The strength test of the pressure relief valve is generally carried out after assembling individual units, but it can also be done after assembly. 　　Duration of strength test: greater than 3 min for DN150 mm. 　　After welding the bellows to the components, a strength test shall be conducted using air at a pressure equal to 1.5 times the maximum pressure after installation of the pressure relief valve. 　　②The sealing test shall be conducted using the actual working medium. When testing with air or water, the test is conducted at 1.1 times the nominal pressure; when testing with steam, it is carried out at the maximum operating pressure permitted at the operating temperature. The difference between the inlet pressure and the outlet pressure must be at least 0.2 MPa. 　　The test method is as follows: after the inlet pressure is set, gradually adjust the adjustment screw of the valve so that the outlet pressure can change sensitively and continuously within the maximum and minimum value ranges, with no stagnation or jamming occurring. 　　Precautions for valve pressure testing: (1) Under normal circumstances, valves are not subjected to strength testing; however, valve bodies and covers that have been repaired, or those that are damaged due to corrosion, should be tested for strength. For safety valves, their set pressure, return pressure, and other tests shall comply with the provisions of their instructions and relevant regulations. 　　(2) The valves after installation shall be subjected to strength and sealing tests. 20% of low-pressure valves shall be inspected randomly; if they fail the inspection, 100% of such valves need to be checked. Medium and high-pressure valves must be inspected 100%. 　　(3) During testing, the valve should be installed in a direction that facilitates inspection. 　　(4) For valves with welded connections, if pressure testing using a blind plate is not feasible, conical sealing or O-ring sealing can be used for pressure testing. 　　(5) During the hydraulic test, exhaust as much air as possible from the valve. 　　(6) The pressure should be increased gradually during testing; sudden and rapid increases in pressure are not allowed. 　　(7) The duration of strength tests and tightness tests is generally 2–3 minutes; for important and special valves, it should be 5 minutes. The testing time for small-diameter valves can be correspondingly shorter, while that for large-diameter valves can be correspondingly longer. During the test, if there are any doubts, the test time can be extended. During strength testing, the valve body and valve cover must not show any sweating or leakage. For seal integrity testing, it is generally performed only once for ordinary valves, while critical valves such as safety valves and high-pressure valves require testing to be carried out twice. During testing, slight leakage is permitted for low-pressure, large-diameter valves that are not critical, as well as those for which leakage is allowed by regulations. Since general-purpose valves, valves used in power plants, marine valves, and other types of valves have different requirements, the specifications regarding leakage must be followed according to the relevant rules. 　　(8) The throttle valve is not subject to a sealing test as a closing element, but it shall be subjected to a strength test as well as sealing tests at the packing and gasket areas. 　　(9) During pressure testing, the valve shall only be closed using the normal physical strength of one person; no tools such as levers may be used to apply force (except torque wrenches). When the diameter of the handwheel is greater than or equal to 320 mm, two people may close it together. 　　(10) Valves with an upper seal should have their packing removed for a sealing test; after the upper seal is installed, check for any leaks. When testing with gas, fill the stuffing box with water for inspection. When performing the filler sealing test, it is not allowed for the upper seal to be in the sealed position. 　　(11) For valves equipped with a driving device, the sealing performance shall be tested by using the driving device to close the valve and conduct the sealing test. For manually driven devices, a sealing test of the valve when closed manually shall also be conducted. 　　(12) The bypass valve installed on the main valve after the strength and sealing tests shall, during the strength and sealing tests of the main valve, open as well when the closing element of the main valve is opened. 　　(13) During the strength test of cast iron valves, use a copper hammer to tap the valve body and valve cover to check for any leaks. 　　(14) When testing valves, except that plug valves allow the application of oil to the sealing surface as specified, oil shall not be applied to the sealing surfaces of other valves during testing. 　　(15) During valve pressure testing, the clamping force exerted by the blind plate on the valve should not be too great, to avoid deformation of the valve and thus affecting the test results; in the case of cast iron valves, excessive clamping force can even cause damage to them. 　　(16) After the valve pressure testing is completed, any water accumulated inside the valve should be removed promptly and the area cleaned, and test records should also be kept.