The valve is a piping accessory used to open and close the pipeline, control the flow direction, and regulate and control the parameters of the conveying medium. Its role is very important, then what types of fluid valves and what are their characteristics.
1, ball valve
When the operating temperature is between -29 degrees and 200 degrees, most manual ball valves are suitable for use in hydrocarbon and utility systems. Ball valves used above 100 °C should be carefully considered. The temperature limit of the soft sealing material should be 100. Above °C. In the case of high temperature or severely 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 available in two designs, namely float and trunnion ball valves. The design of the float ball valve produces high operating torque at high pressure or large pipe diameter, but the seal is better.
2, butterfly valve
Ordinary butterfly valves are suitable for rough throttling and low pressure, hydrocarbon-free, non-hazardous operations. They are not suitable for use as important shut-off valves for vessels, tanks, etc. A wireless butterfly valve should be used at operating conditions above 65oC or pressure levels above ASME 150 or hazardous fluids. Since the butterfly valve can be vibrated to open with a small torque, the handle should be equipped with a locking device. High operating torque is produced at high pressure or large diameter, but the sealing is better.
3, the stop valve
The shut-off valve, also known as the gate valve, is a forced-sealed valve, so when the valve is closed, pressure must be applied to the valve flap to force the sealing surface to not leak. When the medium enters the valve from below the valve flap, the resistance to be overcome by the operating force is the friction between the stem and the packing and the thrust generated by the pressure of the medium. The force of closing the valve is greater than the force of opening the valve, so the valve stem The diameter of the stem should be large, otherwise the valve stem can be bent. When the shut-off valve is opened, the opening height of the valve flap is 25%~30% of the nominal diameter. The flow rate has reached the maximum, indicating that the valve has reached the fully open position. Therefore, the full open position of the shutoff valve should be determined by the stroke of the valve flap.
4, diaphragm valve
In this valve design, the diaphragm valve is connected to the valve stem by a diaphragm made of synthetic rubber. The valve is closed by pressing the diaphragm against the metal boss (which is part of the valve body). Diaphragm valves are primarily used in low pressure waters up to 1400 kPag (200 psig or less) and are especially suitable for systems containing sand and other solid particles.
5, gate valve
Gate valves are suitable for most switching operations, vibration-free hydrocarbons, and utilities in all temperature ranges. In a vibrating operation, the gate valve may be opened or closed from a normal position. Unless the stem packing is carefully adjusted, the torque characteristics of the gate valve are better than those of the ball valve, but there is no convenient operating characteristic of the 90 degree rotation. Manually operated gate valves of size DN50 or larger should be equipped with spring or expansion gates. The gate gate valve usually does not have valve cavity overpressure protection. Unprotected open gate valve, not recommended. Because the marine environment can corrode exposed stems and threads, it is difficult to operate the valve and easily damage the stem packing.
Gate valve with reverse action plate, suitable for automatic shut-off system operation. Simple push-pull operators are available for these valves, thus avoiding the cams of the complex joysticks typically required for ball and plug valves. All movable parts with power operators on the gate valve can be closed, 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 surface. The operating temperature of the soft seal gate valve is limited by the sealing material.
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