Valves are important mechanical devices that help control flow within a variety of applications. With so many different types, it can often be difficult to determine which valve is right for your needs. Although most valves have the same basic purpose, different characteristics and designs make different types better for different situations. Explore our guide below to understand how valves work and the most common types you may encounter. It’s also important to understand the major factors that will help you determine which valve type is the correct choice.
What Is a Valve?
A valve is a device that controls, regulates, or directs the flow within a system or process. They are typically used for controlling a medium, such as a liquid or gas. It operates by opening, closing, or throttling the medium to regulate flow rate or direction of flow. Valves are vital to a wide range of applications, ensuring the efficient and precise management of fluid movement.
Valve Functions
Valves carry out a variety of functions within a fluid system, including:
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On/off control - The most basic function of a valve. On/off valves can start or stop liquid from flowing by opening or closing their passages.
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Flow regulation - Valves can also maintain a predetermined flow rate, throttling the liquid to meet specific needs. Flow rate is the volume of material that moves through your system, usually measured in litres per minute (L/min). Throttling refers to partially closing a valve to regulate flow, without fully opening or sealing.
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Flow direction - Valves can ensure flow is headed in the right direction, or can even change the direction of the entire flow in the system. Achieved by using check valves or multi-port ball valves, which can redirect flow or prevent backflow, which is the reverse movement of fluid.
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Overpressure protection - Valves are crucial for promoting safety. If a pressure spike occurs, then valves can safely relieve pressure by reducing the flow rate and automatically open.
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Excess flow control - A valve can shut off or restrict flow if it detects a sudden increase in flow rate, making it effective against a leak or system failure. Excess flow valves are used in this situation and can be activated to prevent a medium from escaping when the flow increases to a predetermined value.
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Mixing and diverting - Valves can be used to mix different types of fluids. Great for situations where a specific blend or temperature is required within a fluid.
Valve Classifications
Although different valves can achieve the same results, they can have different, unique mechanics. One of the most obvious differences is in how they open and close. Valves will typically fit into one of these categories:
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Linear valves - These use a closure element, such as a disc, plug or diaphragm, that moves in a linear motion to start, stop or regulate flow. Due to its design, linear valves are well-suited for situations requiring precise accuracy and tight sealing.
- Rotating valves - Unlike linear valves, these offer up to 270 degrees of motion. They are great within applications that prioritise a quick turn of the handle for easy opening, closing over precise control.
Beyond the mechanical motion within a valve’s opening, it’s also important to consider the method of actuation, which is the process by which your valve is powered or controlled. Valves usually fall into one of these categories:
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Manual valves - These valves are usually adjusted by the valves lever, or handwheel located on top of the valve.
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Actuated valves - These types of valves are typically connected to some form of mechanical device that operates the valve. They are commonly linked to an electric motor or pneumatic/hydraulic systems, or solenoids. Unlike manual valves, actuated valves are usually used when the force or speed required to operate them exceeds human abilities.
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Automatic valves - These valves don't rely on manual effort to operate. Instead, they function within a system that controls the movement of valves via the actuator by means of inputs and outputs. For example, your neighbours' sprinklers turn on and off by using a simple timer control device.
What Are The Different Types Of Valves
With so many different valves, each with its unique characteristics, we have listed the most common types that are commonly used across a broad range of industries.
Ball valve
One of the most widely used types, which features a hollow ball that rotates within the body of the valve to control flow. Commonly used as a shut-off valve, a simple 90-degree turn of the handle can align the ball with the flow inlet, causing the fluid to flow through. Conversely, if the valve is turned back 90 degrees, the ball blocks the liquid from flowing. Known for being fast and reliable, ball valves are typically quicker and easier to use than gate valves. These two-way valves are great for situations where a quick shut-off is required to prevent spills or leaks that could damage both the system and the environment.
Three-way valves
Commonly used to control flow in multiple directions. Great for when mediums require mixing or simply the diversion of flow from one direction to another. For more complex systems, the use of four-way valves is an ideal method for simplifying a function that would need several valves to achieve the same outcome.
Butterfly valve
In contrast to a ball valve, butterfly valves use a disc that rotates within its body to regulate flow. When closed, the disc sits vertically in the flow path, and rotates parallel to it when it opens, allowing liquid to flow without obstruction. These valves are great for saving space with their wafer-type, compact design.
Check valve
Designed to prevent backflow within piping. The types of check valves within the industry are the swinging flap encased within a flanged body, as well as the ball, cone and needle shaped valves. When your valve is open, the fluid flows through normally. However, whenever any reverse flow is detected, it checks the flow and stops it from passing through. It achieves this by closing the valve using the medium's back pressure and/or with the aid of a spring mechanism attached to the flap, ball or needle. This type of valve is used to protect a system from the medium returning or flowing backwards. Great for use within sewage systems, to stop any sewage from flowing back in the opposite direction.
Gate valve
They are simple in design, using a flat or wedge-shaped gate that moves up and down to control flow. When the gate is up, the medium is free to flow through unobstructed. When the gate is down, the flow is completely shut off. Great in situations that require either a full flow or complete shut-off, such as when a section of pipeline needs to be completely shut off during maintenance.
Knife-gate valve (KGV)
Operates in the same way as a gate valve, just with a flat-plate design. The two main types are: the push-through KGV, where the plate pushes through the seals to open and close; and the standard KGV that pushes into the seal to close. These valves can be metal or resilient seated (non-metal), unidirectional, or bi-directional, depending on the application requirements. This is great for when you're working with slurries like grease, oil, paper or wastewater that could obstruct the flow of other valve types.
Globe valve
These valves have a globe-shaped design with a plug that moves up and down to regulate the flow. This design allows for start/stop functions, with the flow stopping when the plug is down and continuing when it’s raised. They can provide great precision when accuracy on flow rate and pressure is critical.
Needle valve
Very similar design to globe valves, with two key differences. They are typically smaller in design, allowing for finer control of flow through smaller lines. Furthermore, instead of a globe-shaped plug, they use a needle shape, which moves in and out to control flow. Although they can technically be used as an on/off valve, they are great for throttling flow control. Because of their smaller design, needle valves are often used within laboratories in small tubes or pipes, where precise control over flow is vital.
Pinch valve
These valves rely on a flexible rubber tube and a mechanical pinching mechanism to block or restrict flow. The pinching mechanism flattens the tubing to create a seal to stop flow. Because a pinch valve has fewer components than other types, it is a relatively cheaper alternative, and can be used for stop/start and to regulate flow. They are great for liquids, but are unsuitable for gases, because their rubber tubing is unsuitable for high temperatures or pressure.
Pressure reducing valve
A self-acting automatic control valve designed to reduce a higher, unregulated inlet pressure to a constant, lower outlet pressure. It operates independently to maintain downstream pressure, regardless of fluctuations in upstream pressure.
Diaphragm valve
This design features a flexible diaphragm attached to a linear shaft. When the shaft is lowered by the valve stem, the diaphragm seals and cuts off the flow. Because the diaphragm seal and valve body have only contact with the medium, by design, it prevents contamination, making it great for food processing or pharmaceutical sites.
Solenoid-operated valves
Acting more like control units, these valves use electricity to open and close the valve. The actuator plays the role of an electromagnet, which creates a magnetic field to energise and pull up the spring-loaded plunger to open the valve. This design is great for fluid or gas applications where flow is controlled automatically. It can be found anywhere from the refrigerant flow in air conditioners, or water flow in an irrigation system.
Coaxial valve
This valve operates with an internal hollow tube that shifts sideways to control or redirect flow. Typically built from stainless steel, they are an advanced electromechanical device designed to control both fluids and gas flow with precision. Because of its stainless steel design and ability to provide unobstructed flow paths, it is ideal for handling chemicals or any contaminated media.
How To Choose The Right Type of Valve
With so many valve options, it may be difficult to understand how to choose the right one.
- Choice of construction materials - It’s vitally important to understand your valve’s choice of material. Depending on if your valve is processing gases or liquids, your material must be compatible. Typically, plastic valves usually handle corrosive chemicals better than metal, although metal has better temperature resistance.
- Performance criteria assessment - You must determine the pressure and temperature requirements for where your valve will be installed. Usually, different valve designs can handle pressure and temperatures differently. For instance, metal valves are better fitted for higher temperatures and pressures when compared to plastic valves. Specific valve types are also better suited for more extreme performance. Gate valves are a great choice for high-pressure systems, because they prioritise flow isolation and provide a tight seal.
- Valve function - This determines how you want your valve to function within the system. Valves are used to stop and start flow, control the direction of flow, whether it be in one or multiple directions, and to regulate the flow and pressure within the system.
- Fluid type - Your valve type should be able to adequately handle a specific fluid. There are a variety of materials that could alter your choice of valve, including water, gas, oil, or chemicals. For instance, if you are handling anything corrosive or chemical, consider choosing a ball valve, due to its simple design and tight shut-off. If you are dealing with the flow of solids, consider a knife-gate valve, which can work better for slurry type material, etc.
- Maintenance - Ongoing maintenance should be heavily considered when choosing your valve. This is important because it ensures both your valve’s reliability and durability. Your ease of maintenance will depend on your type of valve and the environment in which the valve operates. In critical applications, valves will require a higher level of maintenance.
- Cost - Specific valve types will be more expensive than others. Typically, valves with more complexity will cost more than simpler designed valves, such as ball valves. Other factors that will affect cost include: type of material used, pressure and temperature requirements, size and actuation.
With a variety of valve types suiting many different situations, it may seem like a complex task choosing the right one. Considering each valve type’s specific characteristics and design will allow you to better understand how they can function in your fluid system. When picking the right valve type, it is also important to consult your engineering team to ensure the valve is fit for purpose. At Fluidflo, we can ensure you find the right valve for your specific needs. For more information, please contact our friendly team.