Differences and applications of valves with different connection methods

The difference between different connection methods of valves and the application of valve connection methods refers to the way and specifications of valve and pipeline or equipment connection, the main common ones are flange connection, threaded connection, welding, clamp, ferrule, clamp, etc., this article conducts a detailed analysis of the differences, characteristics and applications of various connection valves.

1. threaded connection valves. This connection is usually made by machining the inlet and outlet ends of the valve into tapered or straight threads, which allow them to be connected to a tapered threaded fitting or pipe. Because of the potential for large leaking channels in such connections, these channels can be plugged with sealants, sealing tape, or packing. If the material of the valve body can be welded, but the coefficient of expansion varies greatly, or the operating temperature varies widely, the threaded connection must be honeysealed. The valves with threaded connection are mainly valves with nominal passage below 50mm. If the bore size is too large, it is difficult to install and seal the connection. To facilitate the installation and removal of threaded valves, fittings are available at the appropriate location in the piping system. Valves with a nominal diameter of less than 50 mm can use a pipe sleeve as a pipe joint, and the thread of the pipe sleeve joint connects the two parts of the connection together.

2. the flange connection valve.
The flange connection valve is easy to install and disassemble. However, it is heavier than the threaded valve, and the corresponding price is also higher. Therefore, it is suitable for pipe connections with various diameters and pressures. However, when the temperature exceeds 350 degrees, the bolts, gaskets and flanges become relaxed, which also significantly reduces the load of the bolts, and leaks may occur in the flange connection with great stress. Flange valves are low in common connections
Flange connection valve installation
1) The specifications and models of the mating flanges are the same; When connected with the flange of the equipment, it should be paired according to its specifications;
2) When the flange is connected, it is coaxial and parallel, and the flange surface is perpendicular to the center of the pipe;
3) The tightening bolt has the same specification and direction, and the exposed length of the bolt is 1/2 of the diameter of the bolt or flush with the nut;
4) When connecting the valve, the nut is placed on the valve side;
5) The top two screw holes of the horizontal pipe flange are kept horizontal, and the vertical pipe flange is against the wall, and the two screw holes are parallel to the wall.

3. Weld the connection valve.
This connection is suitable for a wide range of pressures and temperatures, and is more reliable than flange connections when used in more load-sensitive conditions. However, it is difficult to remove and reinstall welded valves, so its use is limited to situations where it usually operates reliably for a long time, or when the conditions of use are high and the temperature is high. Such as thermal power stations, nuclear energy projects, ethylene projects on the pipeline. For example, high-pressure welded globe valves, welded gate valves.
Welded valves with a nominal diameter of less than 50mm usually have welded sockets to accept the pipe at the load plane end. Because socket welding forms a gap between the socket and the pipeline, it is possible that the gap is corroded by some media, and the vibration of the pipeline will fatigue the connection part, so the use of socket welding is limited to a certain extent.
In the case of large nominal diameter, load engraving and high temperature, the valve body often adopts groove welding, and at the same time, there are original requirements for the welding seam, and the welder must be selected to complete this work.

Installation methods and precautions for welded valves:
Weld bevel
According to the specification requirements, the groove is generally V-shaped, the groove angle is 60-75°, and the gap is 2-3mm.
Weld pairing
The amount of inner wall misalignment should not exceed 10% of the wall thickness, and ≯2mm; The amount of misalignment on the outer wall is ≯3mm.
1) The stainless steel pipe is welded with argon for protection, and the weld and heat-affected zone are pickled and passivated after welding;
2) The brazing of copper pipes shall not be overheated (650-750 °C), and the residual slag and other sundries at the welding joints shall be removed after welding;
3) The appearance inspection of the weld is free of defects such as biting meat, slag inclusion, cracks, and spatter.

The advantages of this form of connection are:
1) Small size, light weight, simple structure, easy to disassemble and assemble;
2) Strong connection force, wide range of use, can withstand high pressure (1000 kg/cm²), high temperature (650 °C) and shock vibration;
3) A variety of materials can be selected, suitable for anti-corrosion;
4) The processing accuracy requirements are not high;
5) Easy to install at high altitude.
Sixth, clamp connection
This is a quick connection method that requires only two bolts and is suitable for low-pressure valves that are frequently disassembled. It is generally found in sanitary valves.