A valve is a mechanical component that controls the flow of a media (gas or liquid) by opening and closing a passageway. Valves are technically fittings as they connect two different components and Figure 1 shows an array of valve types and general fittings. They can be found in virtually every industrial process from chemicals to power generation as well as controlling the water in your home. In this article, we will discuss the purpose of valves, how they operate, and the five most common valve types.
A valve simply controls the flow of a media in a system. Either the flow needs to be regulated to ensure the correct flow rate (control valves or regulating valves) or it can be an intermittent process where the media is needed but not at a consistent flow (shut off valves). They are often connected to pipes, hoses and tubes depending on the type of application. The valves can be operated by hand with a lever or gear wheel, or by a machine remotely utilizing electricity, hydraulics or pneumatics. Depending on the application, different valve types and control mechanisms should be used to minimize cost and maximize performance. They can be as simple as 100% on/off or controlled proportionally depending on how the media needs to be moved from one stage to the next.
Different valve types are meant for different applications and media due to how they operate and the material they are made out of. The five most common valve types are solenoid, ball, butterfly, gate, and check valves.
A solenoid valve is an electromechanically controlled valve, which can be seen in Figure 2. The main components are a solenoid, plunger, spring, seal, and the valve body. They operate by the solenoid, also referred to as a coil, receiving power and creating an electromagnetic field. This field forces the plunger down, against the spring force, and closes the valve orifice (media passageway) with the seal. When power is cut, the spring pulls the plunger back up and the media is free to flow through the orifice. This operation describes a ‘normally open’ solenoid valve and for a ‘normally closed’ solenoid valve it simply works in reverse. Solenoid valves have very fast reaction time and are often used for clean gases and liquids for applications like industrial automation, bottling, or car wash systems.
A ball valve controls the flow of the media by utilizing a rotary ball that has a bore through it, as seen in the sectional view in Figure 3. A ball valve is considered a ‘quarter-turn valve’ as it only requires a quarter turn of the handle to completely open or close the valve. When the handle is in line with the pipe and media flow, the bore is in the flow path and the media is able to flow through the valve. When the handle is turned 90 degrees to be perpendicular to the pipe and valve, the ball and bore is turned and the flow path is closed. This 90-degree rotation can also be performed by utilizing an actuator to turn the valve remotely. Ball valves are durable, reliable, and have a long service life and are often used for water applications, slurries, or any application requiring good sealing.
A butterfly valve operates very similar to a ball valve, is also considered a ‘quarter-turn valve’ and can be seen in Figure 4. When the handle is parallel to the pipe and flow path, the disc is turned to allow media to flow past it. When the handle is turned, the disc also turns and blocks the flow path. Figure 4 shows a butterfly valve with a locking handle that can be locked in the open, closed, or even partially open configuration. Butterfly valves are a smaller cost effective solution compared to a ball valve, but are not as durable and don’t seal as well. However, they are still used for almost any media type, especially in dirty fluid (i.e. oil or beer) applications.
Gate valves simply operate by having a gate raise and lower to open and close the flow path. The gate is connected to a threaded handle and when turned it will move the gate. When it is fully raised, it creates an unobstructed passageway for the flow and allows for easy pipe maintenance (pigging) unlike butterfly valves. As they require multiple turns, they are slower than quarter-turn valves and aren’t as good at proportionally controlling media. However, they are cheap, easy to use, and are widely used for common on/off applications like garden faucets and water lines.
Check valves are also referred to as one-way valves or non-return valves as they only allow media flow in one direction. There is an arrow on the valve body showing the direction of the flow path. If the flow is reversed, the valve will automatically close via a spring or by the high pressure created. They are simple and can operate without the need for automation or a handle. The main purpose of a check valve is to prevent damage to a system if flow was reversed (i.e. if water went through a reverse osmosis system backwards).
Depending on system complexity, most valves can be controlled manually or remotely by electricity, hydraulics, or pneumatics. However, some valves don’t require any control, like a check valve as they only allow flow in one direction.
– Manual: Manually controlled valves either have a handle or a gear wheel. By turning or spinning the mechanism, the valve will open or close. This valve requires human interaction, but often times the manual lever/gear can be replaced with a rotary actuator if there is a desire to automate.
– Electric: An electric valve operates by means of electricity. A solenoid valve uses an electromagnetic field from a solenoid, but you can also utilize electric actuators. These have motors in them that when powered will spin or turn the output, effectively replacing a handle or wheel.
– Hydraulics Pneumatics: Hydraulic (fluid) or pneumatic (gases) actuators operate very similarly as they operate by means of high pressure. It converts this energy into linear or rotary motion that can then control the rotation of a valve stem.
Selecting the appropriate valve requires full application knowledge to ensure the valve will correctly control your fluid. You need to ensure the valve is big enough, effectively seals, effectively controls, and is made of the correct material to withstand the environment and media characteristics. Discuss your application with your valve supplier to choose the correct valve that will keep your system and media up and running.
All Image Sources: https://tameson.co.uk/
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