A valve is a mechanical or electromechanical device used to control the movement of liquids, gases, powders, and more, through pipes or tubes or from tanks or other containers. In most applications, valves rely on a plate, ball, diaphragm, or some other type or mechanical barrier that can be inserted to or removed from the flow stream of the material flowing through. Some valves are strictly of the on/off variety, while others allow the user to control the flow rate of the media traveling through it. The type of material a valve is made from also plays an important role in distinguishing valves and ensuring the compatibility of the wetted parts of the valve with the fluid passing through it. Furthermore, sizing is determined by the pipe or tubing diameter, flow rate, and in pipeline valves being installed as replacements, the width between flanges.
There are many different types of valves that operate in unique ways for specific applications. The six most common, and the six that will be discussed in this blog, are the ball valve, butterfly valve, check valve, gate valve, globe valve, and plug valve.
Ball valves are quarter-turn valves that utilize ported spheres (balls) that swivel in the pipe stream to either block or allow the flow of fluid, though certain designs do allow a degree of flow regulation. The key specifications of a ball valve include the number of ports, configuration of the ports, port connections, valve size, and the materials that make up the valve body, seat, seal, and stem packing. They are ideal for use in any area where fluid flow must be shut off, ranging from compressed-air lines to high-pressure hydraulic systems and more. Because the port can exactly match the pipe diameter, ball valves offer low head-loss characteristics. They also tend to seal better than butterfly valves, though they are generally more expensive to purchase and maintain. In most configurations, the valve is actuated with a lever that provides a visual reference of the valve’s status.
A butterfly valve is a quarter-turn valve that employs centrally-mounted circular flaps that swing into and out of the flow stream. The key specifications of this type of valve include the port connection, valve size, and the materials from which the valve body, seat, seal, disc, and stem packing are constructed. Butterfly valves are used in wastewater plants, power plants, and process plants for shut-off as well as regulating and isolating applications, especially in pipelines with very large diameters. Butterfly valves are generally cheaper and smaller than a ball valve of the same capacity, but do not operate as well against high pressure and flow. Another drawback is that they are more prone to leakage and therefore subject to higher head losses.
Check valves allow fluid to flow through them in one direction only. Many types of check valves exist. Lift-type check valves are similar to ball valves, using a ball or piston backed by a spring that opens under a specified pressure and closes as the pressure decreases to prevent backflow. A variant of this is the stop check valve which doubles as a shut-off valve. Both these types of check valves are suited to high-pressure applications. Another type of check valve, swing check valves, employ spring-actuated hinged gates or wafers that close against ports as pressure diminishes. These are ideal for use in low-pressure applications. Though there is a wide range of types of check valves, they are used in relatively the same manner: anywhere that fluids needs to be transported in a single direction.
Gate valves are rarely used for flow regulation and instead commonly serve to block fluid flow. Gate valves use a plate-like barrier that can be lowered into the flow to stop the stream. Valves of this type operate similarly to globe valves except the gate provides less flow restriction than a traditional globe-valve plug when the valve is fully opened. Gate valves use either wedge-shaped plugs or parallel plates to seal off the stream. Plugs typically seal both the up and downstream sides of the valve while plates only seal the upstream face. To accommodate wear and tear of the sealing surfaces, wedges can take on an array of gate valves. Though they have the advantage of reduced head loss, gate valves are not useful for throttling.
Globe valves are named for their spherical valves bodies and their use of a globe-shaped disc that constricts flow by closing against a restricting orifice. This disc opens and closes either with a handwheel (in manual valves) or an actuator and sliding shaft (in automatic valves). Globe valves are used in wastewater plants, food processing facilities, and process plants for both fluid shut-off and regulating. The most common variety is the Z-style valve, named as such due to the path which the fluid follows through the valve body.
Finally, plug valves are another example of a quarter-turn valve. These valves operate similarly to ball valves, but constrict flow by using a ported plug rather than a ported ball that swivels into the stream. Plug valves are most commonly used for shut-off, but can also be used as controlled valves in chemical process industries, processing plants, wastewater treatment facilities, and more. There are two types of plug valves: lubricated and non-lubricated. Lubricated plug valves use a lubricant between the plug and valve body to act as a sealant, while non-lubricated plug valves instead use a polymeric sleeve to seal and relieve friction.
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