Types and characteristics of fluid valves

1,Ball Valves
When the operating temperature between -29 degrees to 200 degrees, most manual (open and close) ball valves are adapted to hydrocarbon and utility systems in the operation of the ball valves used in more than 100 ℃, the application of the soft sealing material should be carefully considered when the temperature limit should be more than 100 ℃. In high temperature or abrasive 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 are not suitable for throttling because, when the valve is partially open, its sealing surfaces can be damaged by exposure to the process fluid. For critical operations, consideration should be given to the purchase of ball valves equipped with seat and stem lubrication fittings because lubrication prevents minor leakage, reduces operating torque, and, if the valve is required to have both shutoff and relief functions, ball relief holes should be provided independent of the lubrication fittings.

2,Gate Valves
Adaptable to most switching operations, non-vibrating hydrocarbons, and utilities in all temperature ranges. In vibrating operations, gate valves may open or close from their normal position. Unless the stem packing is carefully adjusted, gate valves have better torque characteristics than ball and plug valves, but do not have the ease of operation of a 90-degree swivel action. For manually operated gate valves sized DN50 or larger, they should be equipped with resilient or expansion gates. Deeded gate valves usually do not have cavity overpressure protection. Unprotected open stem gate valves are not recommended. The marine environment can corrode exposed stems and threads, making the valve difficult to operate and prone to stem packing damage. Gate valves with reverse acting plates are adapted for operation in automatic shut-off systems. Simple push-pull operators are available for these valves, thus avoiding the complex lever cams normally required for ball and plug valves. All movable parts of the gate valve with power operators can be enclosed, eliminating contamination due to paint and corrosion products. Gate valves cannot be used in throttling operations. Especially for fluids containing sand, throttling can damage the sealing surfaces. The operating temperature of soft seal gate valves is limited by the sealing material.

3,Check Valve
There are various forms of check valves: including swing, lift and double valve check valves. Among them, the rotary check valve is also used in vertical pipeline (flow direction upward). And this time there is a stop block inside the valve to prevent the valve from opening beyond the upper dead center. Swing check valves cannot be used in vertical pipelines where the flow direction is downward. If used in low fluctuation, low flow rates, swing check valves will vibrate and eventually damage their sealing surfaces. To extend service life, the valve flap can be coated with a tungsten-chromium-cobalt alloy. To minimize seat leakage, resilient seals should be used. Removable seats should be preferred because they are easy to service and allow for easy replacement of the seals in the valve. A screwed or bolted bonnet should be selected for swing check valves to allow inspection and repair of the valve flap and seat. Lift check valves can only be applied to small diameter (DN40), high pressure pipelines handling clean fluids. Lift check valves can be designed to be used on horizontal or vertical pipelines, but the two are not interchangeable. Because lift check valves are usually operated by gravity, they can be affected by paraffin or debris and become clogged. Ball check valves are very similar to lift check valves. Piston check valves are fitted with an orifice plate to control the movement of the piston. Orifice plates for liquids are much larger than those for gases. Piston check valves designed for gas piping cannot be used for liquid service unless the orifice plate in the piston is replaced.

4,Butterfly Valves
Ordinary butterfly valves are suitable for rough throttling and low-pressure, hydrocarbon-free, non-hazardous operations, and they are not suitable for use as important shut-off valves for containers, tanks and so on.

5,Globe Valve
Globe valve belongs to the forced sealing type valve, so when the valve is closed, pressure must be applied to the valve flap to force the sealing surface not to leak. When the medium from below the valve flap into the valve, the operating force needs to overcome the resistance, is the stem and packing friction and the pressure generated by the medium of the thrust, off the valve force than the force of the valve, so the stem diameter should be large, otherwise it will occur stem top bend failure. Globe valve open, the opening height of the valve flap, for the nominal diameter of 25% ~ 30% when. Flow has reached its maximum, indicating that the valve has reached the fully open position. So the full open position of the globe valve should be determined by the travel of the valve flap.

6,Diaphragm Valve
Diaphragm made of synthetic rubber is used in the design of this valve to connect with the valve stem, and closing the valve is achieved by pressing the diaphragm against the metal cam (which is part of the valve body). Diaphragm valves are mainly used in low-pressure water 1400kPag (200psig or less) operations, they are particularly suitable for systems containing sand and other solid particles.
 

7,Plug Valves
Plug valves and ball valves are used in the same range and have similar temperature limits. Plug valves with 90-degree rotary operation are available in both lubricated and non-lubricated designs. Lubricated plug valves must be regularly lubricated with oil, so that its sealing is good, and easy to operate, the number of times of refueling is determined by the conditions of use. Its lubrication feature is a solution for preventing valve jamming. In non-lubricated designs, its sealing is accomplished with Teflon, nylon and other soft materials. They do not require frequent maintenance lubrication, but it is more difficult to rotate the valve after it has been set in one position for an extended period of time. Based on these characteristics, the valve should be selected according to the specific use of the environment.
 

8,Needle Valve
Needle valve is basically a small stop valve. They are often used as instruments and pressure gauges shut-off valves for instrument air, natural gas and hydraulic fluids, small flow throttling, but also used to reduce pressure fluctuations in the instrument piping. Needle valves have very small passages that are easily clogged, and this should be taken into account when using them.