Valve inspection and installation

Inspection before valve installation: ① Carefully check whether the valve model and specifications meet the requirements of the drawings. ② Check whether the valve stem and valve clapper open flexibly, and whether there is jamming or skewing. ③ Check whether the valve is damaged, whether the thread of the threaded valve is correct and intact. ④ Check whether the connection between the valve seat and the valve body is firm, the connection 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 gasket, packing and fasteners (bolts) are suitable for the requirements of the nature of the working medium. ⑥ The pressure reducing valve that is outdated or left for a long time should be disassembled, and debris such as dust and sand should be cleaned with water. ⑦ Clear the port cover and check the degree of sealing. The valve disc must be closed tightly. Valve pressure test: Low pressure, medium pressure and high pressure valves should be subjected to strength test and tightness test. Alloy steel valves should also be subjected to spectrum analysis on the shell one by one, and the material should be reviewed. 1. The strength test of the valve The strength test of the valve is a test when the valve is opened to check the leakage of the outer surface of the valve. For valves with PN≤32MPa, the test pressure is 1.5 times the nominal pressure, the test time is not less than 5min, and there is no leakage at the shell and packing gland. 2. The tightness test of the valve. The test is carried out when the valve is fully closed to check whether there is any leakage on the sealing surface of the valve. Nominal pressure is used. When the working pressure can be determined, the test can also be carried out with 1.25 times the working pressure, and the sealing surface of the valve disc is qualified.

General requirements for valve installation: 1. The valve installation position should not hinder the operation, disassembly and overhaul of the equipment, pipeline and valve body itself, and the aesthetic appearance of the assembly should be considered. 2. For valves on horizontal pipelines, the valve stem should be installed upwards, or installed at a certain angle, and the handwheel should not be installed downwards. The valve, valve stem and handwheel on the high-altitude pipeline can be installed horizontally, and the valve can be opened and closed remotely with a vertical low chain. 3. The arrangement is symmetrical, neat and beautiful; the valve on the standpipe, if the process permits, the valve handwheel is most suitable for operation with chest height, generally 1.0-1.2m from the ground, and the valve stem must follow the operator Direction installation. 4. Valves on side-by-side risers should have the same centerline elevation, and the clear distance between handwheels should not be less than 100mm; valves on side-by-side horizontal pipes should be installed staggered to reduce the distance between the pipes. 5. When installing heavier valves on water pumps, heat exchangers and other equipment, valve brackets should be installed; when the valves are frequently operated and installed more than 1.8m away from the operating surface, a fixed operating platform should be installed. 6. If there is an arrow mark on the valve body, the direction of the arrow is the flow direction of the medium. When installing the valve, make sure that the arrow points in the same direction as the medium flow in the pipeline. 7. When installing flanged valves, ensure that the end faces of the two flanges are parallel and concentric with each other. Double gaskets must not be used. 8. When installing a threaded valve, in order to facilitate disassembly, a threaded valve should be equipped with a union. The setting of the union should consider the convenience of maintenance, usually the water flows through the valve first and then through the union.

Precautions for valve installation: 1. The valve body material is mostly made of cast iron, which is brittle, so it must not be hit by heavy objects. 2. When handling the valve, it is not allowed to throw it by hand; when lifting or hoisting the valve, the rope should be tied to the valve body, and it is strictly forbidden to tie it to the handwheel, valve stem and flange bolt holes. 3. The valve should be installed in the most convenient place for operation, maintenance and overhaul, and it is strictly forbidden to be buried in the ground. The valves on the pipelines in the direct buried and underground trenches shall be equipped with inspection wells to facilitate the opening and closing and adjustment of the valves. 4. Ensure that the thread is intact and undamaged, and wrap the thread with hemp, lead oil or PTFE tape. When screwing, use a wrench to clamp the hexagonal valve body screwed into one end of the pipe. 5. When installing the flange valve, pay attention to tighten the connecting bolts diagonally, and use even force when screwing to prevent the gasket from running off or causing deformation and damage to the valve body. 6. The valve should be kept closed during installation. For threaded valves close to the wall, it is often necessary to remove the valve stem, disc and handwheel during installation before they can be turned. When disassembling, you should turn the handwheel to keep the valve open before disassembling.