Valves are a very important part of any piping system. And there are many different types of valves you will encounter in the chemical industry.
The knowledge of various kinds of valves will definitely help you in your journey in chemical engineering.
So in this post, We are going to learn about valves.
What is a valve?
A valve is a mechanical device that regulates, directs, or controls the flow of fluid. Valves do these by closing, opening, or partially closing the flow area.
When you enter any chemical industry, no matter small, medium, or large scale, you will see tons of different types of valves attached to piping systems.
Valves are everywhere, you can see one in your bathroom which controls the flow of water. Yes, Tap is one type of valve which helps you to control the flow of water that comes from the tank.
Another example of the heart valve is found inside your heart. Your heart contains two chambers and the flow of blood is controlled by valves.
The valve can also be used to reduce the pressure of the gases to reduce its temperature by expanding. A throttling valve is an example of this type of valve.
The valve can not only be used for flow control but can also be used to control the pressure of most gases.
Valves diameter is decided by the pipe on which valve is to be fitted and the pressure drop of the valve is added to the total pressure drop across piping.
The pipe can be joined with a valve by threads (generally used), butt weld (For higher pressure operations), socket weld (for relatively low-pressure operations).
Types of valves
Types of valve based on operation
- Manual valve: This type of valve is operated manually. The upper part of the valve which may be made up of a wheel, lever, or handle is rotated to operate the valve. This type of valve requires high labor costs and a lower level of controllability. But this type of valve requires less maintenance.
- Automatic valve: This type of valve is operated by the control system. The input given by the user on the control panel operates the valves. Pneumatic, Hydraulic, and solenoid valves come under this category. These types of valves utilize compressed air or electric current for the operation of the valves. This type of valve involves no labor cost as it operates itself. Also, this type of valve provides a high level of controllability, and precise operations of closing and opening the valve can be performed. As this type of valve has more parts involves in the operation, Maintenance is high compared to manual types of valve.
Types of valve based on working
Gate Valve
- Type: On/Off
Gate valve is one of the common types of valve found in every process industry. In operation, this valve is positioned completely open or completely closed.
This valve can only be used to start/stop the flow of fluid. The motion of the part of the gate valve called the disk which controls the flow of fluid only does the linear motion.
Gate valve can be best used for pure process fluid or one-phase fluids such as water, gasoline, diesel, air, steam, etc.
Gate valve should not be used for the liquids which contain suspended solids that may get deposited on the seat of the stem which might cause improper shut-off.
As the handle of a gate valve is rotated it transmits its rotation to the stem which linearly comes down. The stem completely sits on the seat and the flow of fluid is obstructed.
Pressure drop across the gate is the valve is low as compared to another type of valve at its open condition.
The major parts of Gate Valve are
- Casing - Casing is the outside body of the valve that protects the valve from the outside environment.
- Bonnet - Bonnet is the outside body of the valve that protects the stem of the valve.
- Port - The flow area of fluid can be obstructed by the stem.
- Stem - Stem does linear motion and obstructs the fluid flow.
- Handle - Handle is rotated to operate the valve
- Seat - The seat is where the stem touches which completely closes the flow area.
Globe Valve
- Type: On/Off/Regulate
Globe valve is the second most used type of valve in the process industry. This type of valve can be used not only for On/Off but also for Throatling operations. In the globe valve flow of fluid is continuously changing. As the handle of the globe valve is rotated its motion is transmitted to the stem which contains the seat fitted with it. The seat (Plug) comes down and fits on another seat made by the metal sheet having a hole at the center. The hole in the metal sheet gets closed by the seat fitted with a stem, This is how the valve is closed. Due to directional change in fluid flow, the globe valve provides a higher pressure drop compared to other valves. As the complex manufacturing of globe valve, it is generally used where we want to partially close the flow area. Shut off in globe valve is superior then gate valve.
Ball valve
Type: On/Off/Regulate
The ball valve is also one of the most used types of valve in the process industry.
The ball valve is a quarter-turn valve which means only 90° Turn is required for the valve to go from open to close.
The ball valve contains the ball as the regulating part which has a hole in the middle of it. The hole of the ball is the same as the size of the pipe fitted with it.
So in open conditions ball valve acts as a simple pipe. But when we rotate the handle of the ball valve, the hole of the ball rotated 90° and the fluid flow gets obstructed by the ball body.
Shut-off in a ball valve is also very good but can not be used for fluid with suspended solids which may get deposited inside the ball cause problem in the operation of the valve.
A ball valve should not be used for fluid with corrosive or hazardous nature because when the ball valve is closed fluid gets trapped inside a ball hole which might cause the problem.
Butterfly Valve
Type: On/Off/Regulate
The butterfly valve is a valve very similar to a ball valve. A butterfly valve is also a quarter-turn valve. A butterfly valve is one of the most widely used valves in the chemical industry.
This valve is widely used because it is cheaper compared to other valves and requires less space for installation.
A butterfly valve is available for a wide range of sizes. Below is an image of a large size butterfly valve.
Check Valve
Type: On/Off
The check valve is one of the special types of valve which is used to prevent backflow.
When the flow is in desired direction check valve completely opens and when any backflow happens valves shut off automatically.
This type of valve is mostly added to piping which fed gas to any equipment because the change in pressure of piping may lead to backflow in the pipe.
Plug Valve
The plug valve is the same as the ball valve but there is a change in the shape of the stem. The stem's shape is a Plugin plug valve. The plug valve has a cavity in it and it obstructs the flow of fluid by rotating inside the flowing region. A plug valve has very similar characteristics to a gate valve.
Needle valve
The globe valve with needle shape stem is called a needle valve. The needle valve is used when accurate flow control is required for small flow rates. A needle valve is often used to control the flow of gases.
Safety Valve
The safety valve is used for systems that deal with gas. When the pressure inside the equipment exceeds the max limit, Safety valves open and reduces the pressure inside the equipment. Due to its working safety valve is also called a pressure relief valve.
Conclusion
So in this article, we learned about what is a valve and learned about different types of valves. If you like the article you can share this article with your friends. Also, you can subscribe to the newsletter to get notified about new articles published.