Process Valves and Their Functions; a Simple Guide
Valves perform different functions in a system, including regulation, control, throttling, safety, and so forth. That is why they come in various types, designs, and materials. There are 9 primary types of valves, including gate valves, ball valves, butterfly valves, check valves, globe valves, plug valves, pinch valves, pressure relief valves, and needle valves. In this guide, we will discuss different process valves and their functions in simple words.
We have already reviewed five main types of valves in our previous blog ‘Main Industrial Valves and Their Applications’, and today we will discuss the other types and categories of valves.
Process Valves and Their Functions in Process Systems
Although plug valves, pinch valves, pressure relief valves, and needle valves are less commonly used compared with the first 5 types of valves discussed in our previous blog, their applications are not less important.
Let’s go over them one by one and find out more about these process valves and their functions.
Type 6. Plug Valves, a Tight-Sealing Valve Ideal for Sewage Systems
The disk in plug valves, which looks like a plug, moves in a rotational fashion to close or open the passageway. As it needs a quarter turn to open and close, it is considered a quick valve. It also offers a tight shut off/on.
As the internal parts of the valve do not come in contact with the fluid, the plug valve is an excellent choice for fluid with debris, very hot media, and higher pressures. It also works well with gas and slurries. For example, plug valves are very popular for sewage systems.
Based on the system’s requirements, you can select the material for the plug valve. It comes in steel, stainless steel, cast iron, aluminum, brass, bronze, PVC, and more.
Plug valves also come in four main types:
- Lubricated plug valves,
- Non-lubricated plug valves,
- Eccentric plug valves,
- Multi-port plug valves.
Advantages of Plug Valves
- The internal parts of the valve are protected against abrasion and corrosion.
- They can tolerate higher temperatures and pressures.
- The multi-port plug valves are great for changing the direction of the flow.
- They have a simple design.
- They can be cost-effective.
- They are easy to maintain.
- They do not cause high pressure drops.
- They offer a long-lasting tight seal.
- They are quick.
Disadvantages of Plug Valves
- Due to the friction, they last longer with actuation than with manual operation.
- They are not a great choice for throttling.
Type 7. Pinch Valves, a Simple Valve Good for Thicker Media
A clamp valve or pinch valve uses a linear motion to stop/start or throttle the fluid. They do not obstruct the passageway, so the fluid can flow without any restriction. Although the design is simple, the media never comes in contact with the valve parts. This isolation has made pinch valves popular for fluids that must not get contaminated.
In addition, pinch valves are suitable to use with slurries and other media with debris. The most common applications of clamp valves are wastewater, cement, and chemical processing. Moreover, they can operate manually or pneumatically.
Pinch valves come in different types:
- Normally open or NO pinch valves,
- Normally closed or NC pinch valves,
- Changeover or CO pinch valves.
They are also available in various materials, such as stainless steel and cast iron for the body, rubber and silicon for the sleeve, and stainless steel or aluminum for the actuator part.
Advantages of Pinch Valves
Their design is simple and easy to fix.
Their maintenance is not difficult and costly.
They can tolerate corrosive fluids very well.
They can protect the fluid from contamination.
Disadvantages of Pinch Valves
They do not work well in higher pressures.
Gas is not a suitable medium for pinch valves.
Type 8. Pressure Relief Valves, a Valve to Ensure Safety
In systems that are susceptible to overpressure, the spring-automated pressure relief valves (also called pressure safety valves or PSVs) can ensure the system’s safety by returning the pressure to the normal level. Otherwise, the system will be damaged or even explode.
On the other hand, if there is a pressure drop, the pressure relief valve increases the pressure to reach the preset normal level. Therefore, the main task of this kind of valve is to maintain the predetermined pressure balance. So, they are usually employed in pressure vessels and boilers.
There are three basic types of pressure relief valves, including
- Conventional spring loaded pressure-relief valve,
- Balanced bellows pressure-relief valve,
- Pilot-operated pressure-relief valve.
PSVs are manufactured in several materials, such as stainless steel, brass, aluminum, plastic, etc. The spring is also made of stainless or carbon steel.
Advantages of Pressure Relief Valves
- They are cost-effective.
- They ensure the system’s safety.
- They can tolerate higher pressures and temperatures.
Disadvantages of Pressure Relief Valves
As the spring should not be corroded, pressure relief valves are not suitable for thicker corrosive media.
Their function might be affected by back pressure, which is why regular maintenance is important.
Type 9. Needle Valves, a Precise Valve for Smaller Systems
Last but not least on our list of process valves and their functions are needle valves. The conical disk in needle valves looks like a needle, hence the name. Needle valves are very precise in controlling the media and are mainly used in smaller systems. They are also a good choice for calibration applications.
The materials needle valves are made of are varied. Most commonly their body comes in stainless steel, brass, and bronze. The seat is also available in PVC, plastic, CPVC, etc. Besides, they can be operated manually, pneumatically, electrically, and hydraulically.
The three basic types of needle valves based on their designs are straight needle valves, angle needle valves, and multiport needle valves.
Advantages of Needle Valves
- They are very accurate and precise in controlling the flow.
- They can be used as regulators.
- It is effortless to seal the valve.
Disadvantages of Needle Valves
- They cannot tolerate high flow rates.
- To turn them on/off, they need a few turns.
Other Classifications of Valves
To complete our discussion of process valves and their functions, it’s good to review other classifications of valves. There are three more basic valves classifications based on
- Their functions,
- Their opening method,
- Their operating method.
Let’s go over them briefly.
Classifying Valves by Function
As we have seen, each type of valve is most suitable to carry out a certain function or functions. That is why, one of the best ways to categorize valves is by their function. Based on this, valves fall into five main categories. However, a specific type of valve can belong to more than one function group.
1. Isolation Valves
The most important function of an isolation valve in a system is to prevent the media from flowing into a specific part. The other application is for the manual control of the media.
Some examples of isolation valves include butterfly valves, ball valves, plug valves, pinch valves, gate valves, and diaphragm valves.
2. Regulating Valves
The main purpose of a regulation valve is to make some adjustments to different parameters in a system. For instance, the pressure, temperature, flow rate, etc. That is why they are also known as adjustment valves.
Ball valves, needle valves, globe valves, and plug valves are a few examples of regulating valves.
3. Safety Relief Valves
Safety relief valves are used to avoid damage to the system or explosion due to build-up pressure or temperature. Pressure relief valves (PRV) and vacuum relief valves are two common examples.
4. Non-Return Valves
The purpose of a non return valve is to make sure the media is flowing in the right (and one) direction. So, they prevent any reverse of the flow, which can cause problems for the system. Different types of check valves belong to this category.
5. Special Purpose Valves
Special-purpose valves are designed in a way to carry out more duties and functions than control, check, and two-way isolation valves. For example, multi-port valves can direct the flow in up to 5 different directions. Knife gate valves, float valves, and line blind valves are some other examples of special purpose valves.
Types of Valves Based on Their Opening Methods
Valves open and close by two basic methods.
- Quarter-turn valves: To fully open and close these valves, you just need to turn the handle 90 degrees. That is why it is really easy and quick to operate them. However, they are not suitable for more precise purposes.
- Multi-turn valves: Unlike the quarter-turn valves, you need to turn the handle a few times to fully open or close a multi-turn valve. But they vary in their speed based on their design.
Valve Types Based on Their Operating Methods
Although you can operate valves mechanically by turning the handle, this is not the only way. There are mainly three ways to operate valves.
- Manual operation: This is the most basic way of operating a valve. It can be done by a handle, a gear wheel, a handwheel, a hand level, etc.
- Actuated valves: When an actuation is mounted on the valve, it makes it possible to operate it remotely in different ways, including electrically, pneumatically, hydraulically, and solenoid.
- Automatic operation: These valves are triggered by a parameter in a system, such as flow rate, temperature, pressure, and other factors. Usually, they act according to some predetermined presets.
Now that you learned about process valves and their functions, and different classifications of valves, you can find the right valve for your system more easily. Look up what you want on our products page here.
Process Valves and Their Functions FAQs
Let’s answer some of your frequent questions about industrial valves and their applications.
How Can I Maintain the Valves in a Piping System?
Clean the valves regularly, check the whole system often, lubricate the valves, and if you are not using them for a while, wrap them.
What Type of Process Valves Is More Common in Chemical Industry?
As controlling the flow rate accurately is usually vital in the chemical industry, gate valves are the most commonly used ones.
What Factors Should I Consider When Choosing a Valve?
Choosing the right valve for the system is one of the most important decisions when it comes to the process industry. Some of the factors you must consider include
- Size and diameter,
- Purpose and function,
- Chemical compatibility between the valve material and the fluid,
- Pressure and temperature.
What Is a Good Throttling Valve?
Butterfly valves are usually considered one of the best for throttling.
What Type of Valve Is the Most Common One?
Ball valves are very popular and common. One reason can be their simple and easy operation.
Other Process Equipment You Might Need
We have reviewed the main points and facts about the nine main process valves and their functions. Besides, different valve opening and operating methods have been introduced. However, valves are not the only thing we need in a process system.
At Process Valve and Instruments in Alabama, we supply any type of process equipment and deliver it across the US. Our team of experts also offers you advice on the right equipment for your specific purpose. Call us at 800-749-8068 from 8 am to 5 pm.