Types of valves in the chemical industry
1 Ball Valve (Ball Valve)
When the operating temperature is between -29oC and 200oC, most manual (opening and closing) ball valves are suitable for the operation of hydrocarbons and utility systems. For ball valves used above 100oC, the temperature limit of the soft sealing material should be carefully considered during application. Above 100oC. In high temperature or severe abrasion operations, the application of metal-sealed ball valves should be considered, but it should be noted that the operating torque must be increased.
——Ball valves have two designs, namely floating ball and trunnion ball valves. The design of the floating ball valve will produce high operating torque under high pressure or large pipe diameter, but the sealing performance is better.
——The ball valve is not suitable for throttling, because when the valve is partially opened, its sealing surface will be exposed to the treatment fluid and be damaged.
——For critical operations, you should consider buying a ball valve equipped with ball seat and stem lubrication fittings, because lubrication can prevent minor leakage and reduce operating torque. If the valve is required to have both shut-off and release functions, then A ball relief hole independent of the lubrication fittings shall be provided.
2 Globe Valve Gate valve is suitable for most switching operations, vibration-free hydrocarbons and utilities in all temperature ranges. During operation with vibration, the gate valves may open or close from their normal positions. Unless the stem packing is carefully adjusted, the torque characteristics of gate valves are better than ball valves and plug valves, but they do not have the convenient operating characteristics of 90-degree rotation.
——For manually operated gate valves with a size of DN50 (2 in) or larger, an elastic gate or an expansion gate should be equipped. Wedge gate valves usually do not have valve chamber overpressure protection.
——Unprotected rising stem gate valve is not recommended. Because the marine environment will corrode the exposed stem and threads, the valve is difficult to operate and the stem packing is easily damaged.
——Gate valve with reverse acting plate, suitable for automatic shut-off system operation. For these valves, a simple push-pull operator can be used, thus avoiding the complicated operating lever cam required for ball valves and plug valves. All movable parts with power operators on the gate valve can be closed, eliminating the pollution caused by paint and corrosion products.
——The gate valve cannot be used in throttling operations. Especially for fluids containing sand, throttling can damage the sealing surface.
——The operating temperature of the soft sealing gate valve is limited by the sealing material.
3 Check Valve
Check valves come in various forms: including swing, lift, ball, piston and separate disc swing check valves. Among them, the fully open swing check valve is suitable for most non-fluctuation situations. Swing check valves are also used in vertical pipelines (upward flow direction). At this time, there is a stop block in the valve to prevent the valve flap from opening beyond the top dead center.
swing check valve cannot be used on vertical pipelines with downward flow direction. If used in places with low fluctuations and low flow rates, the swing check valve will vibrate and eventually damage its sealing surface. In order to extend the service life, the valve disc can be coated with a layer of stellite. In order to reduce the leakage of the valve seat, an elastic seal should be used. Removable valve seats should be preferred because they are easy to repair and easy to replace the seals in the valve.
Swing check valve should use a screw or bolt connection bonnet to check and repair the valve clack and valve seat. In many cases, the minimum size of the repairable high-pressure swing check valve on the pipeline can be DN65 (2.5NPS) or DN80 (3NPS).
——Thin design of rotary check valve (space saving), suitable for installation between two flanges. This type of check valve does not fully open normally and needs to be removed from the pipeline for repairs.
——The double disc thin check valve occupies a small space and is light in weight, so it is usually used in offshore oil. Since fatigue can cause the spring to fail, the double-disc thin check valve cannot be used for pulsation operations. But you can consider using non-impact (or automatic) check valve or rotary check valve.
——Lift check valve can only be used to handle clean fluids on small diameter (DN 40), high pressure pipelines. Lift check valves can be designed to be applied to horizontal pipelines or vertical pipelines, but the two are not interchangeable. Because lift check valves are usually operated by gravity, they may be blocked by paraffin or debris.
——Spherical check valve is very similar to lift check valve. Because the ball is lifted by liquid pressure, this type of check valve does not have the tendency of the flap to close and strike like a rotary check valve. Therefore, it is better for clean fluids that frequently change the direction of flow in a pipeline not larger than DN 50 (2 in).
——Self-balancing, axial piston, non-automatic check valve, it is recommended to be used in pipelines with fluctuating flow, such as the outlet pipeline of reciprocating compressors and pumps. They are not suitable for use in pipelines with sand or impurities in the fluid. The piston check valve is equipped with an orifice to control the movement of the piston. The orifice plate for liquids is much larger than the orifice plate for gases. Piston check valves designed for gas pipelines cannot be used for liquid operations unless the orifice in the piston is replaced.
4 Butterfly Valve (Butterfly Valve)
Ordinary butterfly valves are suitable for rough throttling and low pressure, hydrocarbon-free, and non-hazardous operations. They are not suitable for important shut-off valves for containers and tanks. In working conditions where the temperature is higher than 65oC or the pressure level is higher than ASME 150 or dangerous fluids, wireless butterfly valves should be used. Because the butterfly valve can be opened by vibration with only a small torque, the handle should be equipped with a locking device.
5 shut-off valve
When a good throttling control is required (such as a bypass pipe of a control valve or a small exhaust hole), the stop valve is the most suitable.
6 Diaphragm valve (chip type)
In the design of this valve, a diaphragm made of synthetic rubber is connected to the valve stem, and the valve is closed by pressing the diaphragm on a metal boss (which is a part of the valve body). Diaphragm valves are mainly used in low-pressure water 1400 kPag (200 psig or less) operations. They are especially suitable for systems containing sand and other solid particles.
7 Plug Valve (Plug Valve)
The use range of the plug valve and the ball valve are the same (refer to section 1), and the use temperature limits are also similar. The plug valve with 90 degree rotation operation is available in both lubricated and non-lubricated designs. Lubricated plug valves must be lubricated regularly to make them have good sealing performance and easy to operate. The number of lubrication depends on the conditions of use. Its lubrication function is a solution to prevent the valve from jamming.
In the non-lubricating design, its sealing is done with Teflon, nylon and other soft materials. They do not require frequent maintenance and lubrication, but when the valve is set in one position for a long time, it is more difficult to rotate again. Based on these characteristics, the valve should be selected according to the specific use environment (conditions).
8 Needle Valve (Needle Valve)
Needle valve is basically a small shut-off valve. They are often used as shut-off valves for instruments and pressure gauges, for small flow throttling of instrument air, natural gas and hydraulic fluids, and for reducing pressure fluctuations in instrument pipelines. The passage of the needle valve is very small and it is easy to be blocked. This should be considered when using it.
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