• Inspection and installation of valves (part one)

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Inspection and installation of valves (part one)

  • Sep 18, 2018
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Inspection before valve installation
1 Check carefully whether the type and specifications of the valve meet the requirements of the drawing or not.
2 Check if the stem and disc opening are flexible, with or without jamming and skewing.
3 Check whether the valve is damaged and whether the thread of the threaded valve is clear and intact or not.
4 Check if the seat and the valve body are firmly bonded, the valve disc and the valve seat, the valve cover and the valve body, and the valve stem and the valve disc are connected.
5 Check if the valve gasket, padding and fasteners (bolts) are suitable for the nature of the working medium.
6 Old or long-lasting pressure reducing valves should be disassembled, dust, sand and other debris must be cleaned with water.
7 Clear the end seal-capping, check the sealing degree, and the valve flap must be closed tightly.

Pressure test of valves
For low-pressure, medium-pressure and high-pressure valves, strength tests and tightness tests are to be carried out. Alloy steel valves are also subjected to spectral analysis of the shells one by one, and the materials are to be recheck.
1. Strength test of the valve
The strength test of the valve is performed under the open state of the valve to check the leakage of the outer surface of the valve. For valves with PN ≤ 32 MPa, the test pressure is 1.5 times the nominal pressure, the test time is not less than 5 min, and no leakage at the shell and packing gland is desirable.
2. Tightness test of the valve
The tightness test is carried out under the condition that the valve is completely closed, to check whether there is leakage on the sealing surface of the valve, and the test pressure, except the butterfly valve, check valve, bottom valve, and throttle valve, should generally be carried out under nominal pressure. At the working pressure, the test can also be carried out with a pressure of 1.25 times nominal pressure, and the valve sealing surface with no leakage is qualified.

General rules for valve installation
1. The position of the valve installation should not impede the equipment, the operation of piping and valve body itself, disassembly, assembly and maintenance. Meanwhile, the aesthetic appearance of the assembly should be take into account.
2. Install the valve on the horizontal pipe with the valve stem facing up or at a certain angle. Do not install the hand wheel downward. The valves, stems and hand wheels on the high-altitude pipeline can be installed horizontally, and the valve is opened and closed remotely with a chain that is vertically lower.
3. Arranged symmetrical, neat and tidy, for the valve on the stand pipe, under the premise of the process, it is most suitable for the valve hand wheel to be installed at the chest height, generally 1.0-1.2m from the ground, and the valve stem must be installed in concert with the operator direction.
4. The valves on the side-by-side stand pipes should have the same center line elevation and the clearance between the hand wheels should not be less than 100mm. The valves on the side-by-side horizontal pipes should be staggered to reduce the pipe spacing.
5. When installing heavier valves on pumps, heat exchangers, etc., valve brackets should be provided; when frequently operating valves installed more than 1.8m from the operating surface, a fixed operating platform should be provided.
6. There is an arrow mark on the valve body, and the direction of the arrow is the flow direction of the medium. When installing the valve, care should be taken to point the arrow at the same direction as the media in the pipe.
7. When installing the flange valve, ensure that the end faces of the two flanges are parallel and concentric with each other. Do not use double gaskets.
8. When installed, a threaded valve should be matched with a loose joint for ease of disassembly. The setting of the joint should coincide with the convenience of maintenance. Usually, the water flow passes through the valve and then passes through the joint.