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25
2022
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02
Several connection methods for gate valve bonnet
The valve cover and body of the stop valve can be connected by thread, flange, welding and other methods, or by pressure self-sealing device, or the valve cover and body can be made into a whole without connection. The following editor introduces several connection methods.
The bonnet and body of the stop valve can be connected by thread, flange, welding, etc., or by a pressure self-sealing device. The bonnet and body can also be made as a whole without connection. The following describes several connection methods.
1. Threaded Bonnet
This threaded bonnet has a simple structure and low price. However, the gasket of the bonnet is in close contact with the rotating surface, and loosening or tightening the bonnet may damage the joint surface. If the valve size is large, the torque required to tighten the bonnet is large. Therefore, the threaded bonnet is limited to valves with a nominal size of no more than DN80.
The bonnet can also be connected to the body through a separate threaded ring sleeve. The advantage of this structure is that the joint is tight, so the joint will not move relative to each other. Therefore, even if the bonnet is tightened frequently, the joint surface is not easily damaged. Like the threaded bonnet, the bonnet connected by the threaded ring sleeve is limited to valves with a nominal size of no more than DN80. If the bonnet is made of weldable material, the threaded bonnet can be sealed by welding.
2. Welded Bonnet
The welded bonnet structure is not only economical but also reliable, and is not limited by the valve diameter, working pressure, and temperature. However, its disadvantage is that it is difficult to maintain. Only by machining off the weld can the inside of the valve be accessed. Therefore, welded bonnets are usually only used for valves that do not require long-term maintenance, disposable valves, or valves where it is more difficult to seal the bonnet connection than to disassemble and repair the valve.
3. Flanged Bonnet
The flanged bonnet is superior to the threaded bonnet because its tightening force can be distributed to all the bolts. Therefore, the flanged bonnet can be used on valves of any diameter and pressure rating. However, as the valve size and pressure increase, the volume and weight of this structure of valve become larger and larger. When the working temperature of the valve is higher than 350℃(600℉), the bearing capacity of the bolts will be greatly reduced due to creep relaxation. Seal welding can also be used for flange connections in demanding applications.
4. Pressure Self-Sealing Bonnet
Pressure self-sealing bonnet, this structure presses the joint surface through the medium pressure, overcoming the disadvantage of large weight of other structures. Moreover, as the medium pressure increases, the sealing of the bonnet becomes tighter and tighter. This structure has become the bonnet connection method for high-temperature and high-pressure large valves.
The pressure self-sealing structure at the connection between the body and the bonnet provides a tight seal between the body and the bonnet through the pressure of the fluid inside the valve. At present, there are two types of pressure self-sealing: metal sealing ring and composite sealing ring (flexible graphite + 304 stainless steel wire). The metal sealing ring is made of low carbon steel and the outer surface is silver plated. Silver has good plasticity and can easily fill the micro-pores on the sealing surface, thus ensuring the sealing performance of the sealing ring under high pressure.
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