Common valve installation knowledge I

Author:     Published time:2022-04-24 09:30     Reading times:259    

Inspection and installation of valves

Inspection before valve installation

① Carefully check whether the valve model and specification meet the requirements of the drawing.

② Check whether the valve stem and disc can be opened flexibly and whether they are stuck and skewed.

③ Check whether the valve is damaged and whether the thread of the threaded valve is correct and complete.

④ Check whether the combination of valve seat and valve body is firm, the connection between valve disc and valve seat, valve cover and valve body, and the connection between valve stem and 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 old or long-standing pressure reducing valve shall be disassembled, and the dust, sand and other sundries shall be cleaned with water.

⑦ Clear the port cover, check the sealing degree, and the valve disc must be closed tightly.

Pressure test of valve

Strength test and tightness test shall be conducted for low-pressure, medium pressure and high-pressure valves, and spectral analysis shall be conducted for the shell of alloy steel valves one by one to recheck the material.

1. Strength test of valve

The strength test of the valve is to check the leakage on the outer surface of the valve when the valve is open. For valves with PN ≤ 32Mpa, the test pressure is 1.5 times of the nominal pressure, the test time is not less than 5min, and it is qualified if there is no leakage at the shell and packing gland.

2. Valve tightness test

For the test conducted when the valve is fully closed, check whether there is leakage on the sealing surface of the valve. The test pressure, except for butterfly valve, check valve, bottom valve and throttle valve, shall generally be carried out at the nominal pressure. When the working pressure can be determined, the test can also be carried out at 1.25 times the working pressure, and the valve disc sealing surface is qualified if there is no leakage.

General provisions for valve installation

1. The installation position of the valve shall not hinder the operation, disassembly and maintenance of the equipment, pipeline and valve body, and the beauty of the assembly appearance shall be taken into account.

2. The valve stem on the horizontal pipeline shall be installed upward or inclined at a certain angle, and the handwheel shall not be installed downward. The valve, valve stem and hand wheel on the high-altitude pipeline can be installed horizontally, and the opening and closing of the valve can be remotely controlled by the vertical low chain.

3. The arrangement is symmetrical, neat and beautiful; For the valve on the riser, if the process permits, the valve handwheel is most suitable for operation at chest height, generally 1.0-1.2m from the ground, and the valve stem must be installed along the direction of the operator.

4. Parallel the valves on the riser. The elevation of the center line should be the same, and the clear distance between the hand wheels should not be less than 100mm; Valves on side-by-side horizontal pipelines shall be installed staggered to reduce pipeline spacing.

5. When installing heavy valves on water pumps, heat exchangers and other equipment, valve supports shall be set; When the valve is operated frequently and installed more than 1.8m away from the operating surface, a fixed operating platform shall be set.

6. If there is an arrow mark on the valve body of the valve, the direction of the arrow is the flow direction of the medium. When installing the valve, pay attention to make the arrow point to the same direction as the medium flow in the pipeline.

7. When installing flange valves, ensure that the end faces of the two flanges are parallel and concentric with each other, and double gaskets shall not be used.

8. When installing threaded valves, in order to facilitate disassembly, a threaded valve shall be equipped with a union. The setting of the union shall 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 of the valve is mostly made of cast iron, which is brittle, so it shall not be impacted by heavy objects.

2. When handling the valve, it is not allowed to throw it at random; When lifting and hoisting the valve, the rope shall be tied to the valve body and shall not be tied to the hand wheel, valve rod and flange bolt hole.

3. The valve shall be installed in the most convenient place for operation, maintenance and overhaul, and it is strictly prohibited to be buried underground. Inspection chambers shall be set for valves on pipelines directly buried and in trenches to facilitate the opening, closing and adjustment of valves.

4. Ensure that the thread is intact, and wrap hemp, lead oil or PTFE raw material belt on the thread. When screwing, 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 along the diagonal direction, and the force shall be uniform when screwing, so as to prevent the gasket from deviation or deformation and damage of the valve body.

6. The valve shall be kept closed during installation. For threaded valves close to the wall, the valve stem, disc and hand wheel often need to be removed before they can be screwed. During disassembly, the hand wheel shall be turned to keep the valve open before disassembly.