A comprehensive guide to the inspection and installation of valves

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Inspections before valve installation ① Carefully check and verify that the valve model and specifications meet the requirements of the drawings. ② Check whether the valve stem and valve disc open smoothly, and whether there is any sticking or misalignment. ③ Check whether the valves are damaged, and whether the threads on threaded valves are straight and intact. ④ Check whether the valve seat is firmly bonded to the valve body, as well as the connections between the valve disc and the valve seat, the valve cover and the valve body, and the valve stem and the valve disc. ⑤ Check whether the valve gaskets, packing, and fasteners (bolts) are suitable for the requirements of the working medium. ⑥ Old or long-idle pressure relief valves should be removed, and debris such as dust and sand must be cleaned off with water. ⑦ Remove the vent cover and check the sealing; the valve disc must close tightly. Pressure testing of valves: Low-pressure, medium-pressure, and high-pressure valves must undergo strength tests and tightness tests. For alloy steel valves, spectral analysis of the casing must be carried out individually to verify the material composition. 1. Strength test of the valve: The strength test of the valve is conducted with the valve in the open position, in order to check for any leaks on the outer surface of the valve. For valves with PN≤32MPa, the test pressure is 1.5 times the nominal pressure, and the test duration must be at least 5 minutes; the valve is considered qualified if there is no leakage at the shell or the packing gland. 2. Leakage test of valves: This test is conducted when the valve is completely closed, to check whether there are any leaks at the valve’s sealing surfaces. For valves other than butterfly valves, check valves, foot valves, and throttle valves, the test pressure should generally be equal to the nominal pressure. When the operating pressure can be determined, a test pressure equivalent to 1.25 times the operating pressure may also be used. The test is considered successful if no leakage occurs at the valve’s sealing surfaces. General provisions for valve installation: 1. The location where the valve is installed should not hinder the operation of the equipment, pipelines, and the valve itself, nor should it complicate its disassembly, assembly, and maintenance. At the same time, attention must be paid to the aesthetic appearance of the overall assembly. 2. For valves on horizontal pipes, the valve stem should be installed facing upward or at a certain angle; it must not be installed with the handwheel pointing downward. The valves, valve stems, and handwheels on high-altitude pipelines can be installed horizontally, with chains positioned at a lower vertical position being used to operate the opening and closing of the valves from a distance. 3. Symmetric arrangement, neat and aesthetically pleasing ； For the valves on the risers, as permitted by the process requirements, it is most convenient to operate the valve handwheel at chest height; generally, a height of 1.0–1.2 meters above the ground is suitable, and the valve stem must be installed in the direction of the operator. 4. For valves on parallel vertical pipes, it is advisable that their centerlines be at the same elevation, and the clear distance between the handwheels should be no less than 100 mm ； Valves on parallel horizontal pipes should be installed offset from each other to reduce the pipe spacing. 5. When installing heavier valves on equipment such as water pumps and heat exchangers, valve supports should be provided ； For valves that are operated frequently and are installed at a height of more than 1.8 m above the operating surface, a fixed operating platform should be provided. 6. If there are arrow marks on the valve body, the direction indicated by the arrows is the flow direction of the medium. When installing the valve, care should be taken to ensure that the arrow points in the same direction as the flow of the medium within the pipe. 7. When installing flanged valves, it is necessary to ensure that the two flange faces are parallel and concentric; dual gaskets shall not be used. 8. When installing threaded valves, to facilitate disassembly, one threaded valve should be equipped with a union. The installation of the union should take into account ease of maintenance; usually, the water flow passes through the valve first and then through the union. Precautions for valve installation: 1. The body of valves is usually made of cast iron, which is brittle; therefore, it must not be struck by heavy objects. 2. When handling valves, they must not be tossed carelessly ； When lifting valves, the rope should be tied to the valve body; it is strictly prohibited to tie it to the handwheel, valve stem, or flange bolt holes. 3. Valves should be installed in locations where operation, maintenance, and repair are easiest; it is strictly prohibited to bury them underground. For valves on pipes buried directly in the ground or in trenches, inspection chambers should be provided to facilitate the opening, closing, and adjustment of the valves. 4. The threads must remain intact and undamaged; hemp should be wrapped around them, lead paint applied, or PTFE tape used. When tightening, a wrench should be used to hold the hexagonal valve body at one end of the pipe in place. 5. When installing flanged valves, be careful to tighten the connecting bolts in a diagonal direction, applying even force while tightening to prevent the gaskets from shifting or to avoid deformation and damage to the valve body. 6. The valve should be kept closed during installation. For threaded valves located close to a wall, it is often necessary to remove the valve stem, disc, and handwheel during installation in order to turn them. When disassembling, the valve should be kept open by turning the handwheel before proceeding with the disassembly.