Flange connection, which refers to the detachable connection of the flange, washer and bolt as a set of combined sealing structures, is the most used form of connection between valves and piping or equipment. The flange connection uses conveniently and can withstand large pressures. Flange connection can be applied to forged steel valves of various nominal sizes and nominal pressures, but there are certain restrictions on the use temperature. When in high temperature conditions, the connecting bolts of flanges are prone to creep and will cause leakage. In general, flange connections are recommended for use at temperatures lower than or equal to 350 °C.
Flange connection can be divided into the following types according to the shape of the bonding surface:
Smooth: Easy to process, and for low pressure valves.
Unevenness: Used in high working pressure conditions, medium hard washer can be used.
Tongue and groove: It can be used washer with large plastic deformation, which is widely used in corrosive medium with good sealing effect.
Trapezoidal groove: Use oval metal ring as washer, for valves with working pressure greater than or equal to 60/100 kg/cm2 or high temperature valves.
Lens: The washer is in the shape of a lens and is made of metal, for high pressure or high temperature valves with working pressure greater than or equal to 100 kg/cm2.
O-ring: It is a relatively new flange connection whose sealing effect is more reliable than the general plain washer.
The welded joint refers to a connection form in which the valve body has a welded groove and is connected to the piping system by welding. The welding connection between valve and pipeline is divided into butt welding connection (BW) and socket welding connection (SW). Butt welding connection (BW) can be applied to various sizes, various pressures and high temperature conditions. Socket welding connection (SW) is generally applicable to the valve lower than or equal to DN50.
Threaded connections are a convenient method of connection and are often used in small forged steel valves. There are two cases:
Direct sealing: Internal and external threads seal directly. In order to ensure that the joints are not leaking, they are often filled with lead oil, wire hemp and polytetrafluoroethylene raw material tape, and the polytetrafluoroethylene raw material tape is widely used. This material has excellent corrosion resistance, great sealing effect, easy to use and store, and can be completely removed when disassembled, because it is a non-stick film, which is superior to lead oil and wire.
Indirect sealing: The force that facilitates the tightening of the thread is transmitted to the washer in two planes, allowing the washer to seal.
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