Understand what valves are, the types of valves that exist, and their uses within piping. In this guide, learn specifically about ball valves, gate valves, globe valves, butterfly valves, check valves, pressure relief valves, and pressure regulating valves.
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What Is A Valve?
A valve is a device used to decrease or stop the flow of a fluid in piping. It is a type of pipe fitting that controls the flow inside a pipeline.
Valves can be operated manually by turning the handle of the valve, or automatically by using a pressure difference and an actuator. An actuator is a device that automatically controls the valve on or off.
Types of Valves
There are two categories of valves for piping: shut off valves and regulatory valves. Within each category, there are many types of valves, each with their own handle and use. The types of valves that we'll cover in this guide are:
Shut Off Valves
Shut-off valves that are used primarily to start or stop the flow of fluid in the pipe. A shut-off valve can be operated manually, or automatically using external control such as an actuator. An electric motor is a type of actuator that can be used to rotate the handle of a valve. This way the shut-off valve can be operated automatically.
There are many types of shut off valve:
Ball valve
Gate valve
Globe valve
Butterfly valve
Ball Valves
Ball valves are 2-way, 2-position valves used for shut-off or isolation of a system. 2-way valves mean there are two ports (in and out of pipe) and 2-position valves refer to open or closed.
Ball valves can also be 3-way or 4-way. Such multi-port valves are used in piping that require more than one source of flow. For example, if your home is equipped with two sinks. To stop the water supply from one of the sinks, you may use a 3 way shut-off valves.
A ball valve controls a liquid or gas flow using a rotary ball with a hole in the middle. When we rotate the ball valve, the ball aligns with the valve cylinder. This allows liquid or gas to flow through. A slot is machined on the top of the ball. The stem fits into this slot and is bolted to the handle on the other end. As you turn the handle, it turns the ball to open or close the valve.
Ball valves have a fast shut-off with only a quarter-turn or 90° turn to close the valve. This makes them easier to use for applications where frequent opening and closing is required.
Gate Valves
Gate valves work by inserting a rectangular gate or wedge into the path of a flowing fluid. Similar to a ball valve, the stem is connected to the handle of the gate valve. The other end of the stem is connected to a rectangular wedge.
When the hand-wheel is turned, it rotates the stem. This makes the threads on the stem unscrew. Due to movement of the threaded rod, the rectangular wedge attached at the other end of the stem also moves up. This opens the valve and fluid flows through the pipe.
Gate valves are similar to old water taps. They are considered multi-turn valves, as it takes more than one 360° turn to fully open or close the valve. Due to this reason, they are used in applications that does not require frequent opening and closing. Gate valves are easier to clean and maintain though, making them suitable for applications that involve slurries.
Globe Valves
A globe valve is used to stop, start and regulate flow. Unlike a gate valve, a globe valve can control the flow of fluid. A 2-way globe valves are used for single inlet flow and outlet flow. When more than one inlet and single outlet, a 3 way or 4 way globe valves is used.
In globe valves, a disc is used to block the flow through the pipe. The other parts used such as stem, bonnet are similar to gate valves. The disc within the globe valve is designed to move up and down from the seat. These vertical movements allow the space between the disc and the seat to change slowly, giving the valve good control over flow of fluid through the pipeline. The further apart the disc and seat, the more liquid that will flow through the valve. This control of fluid flow is not possible in a gate valve.
The workings of a globe valve is similar to tap used in wash basin and kitchen; as you rotate the tap handle, fluid flow starts gradually and will reach maximum when fully opened. In a globe valve, when the disc is fully lowered, the fluid flow is shut off. When the disc is fully raised, the fluid flows at its maximum rate.
Globe valves are used for regulating and shut off applications in swimming pool drains and lubrication systems. All these systems require starting, stopping and regulating flow for its application.
Butterfly Valves
Butterfly valves are shut-off valves that are used to start and stop liquid flow. They are made to be specifically compact for tight spaces.
In butterfly valves, a disc is used similarly to a globe valve. When the disc within a butterfly valve is completely sideways, fluid is permitted to flow; when the disc of a butterfly valve is upright, the flow of fluid is blocked completely.
Butterfly valves are a quarter turn rotational motion valve, making them great for quick-acting situations. Similarly to ball valves, butterfly valves are easier to use for applications where frequent opening and closing is required.
Regulating Valves
While shut-off valves are used to start and stop the flow inside the pipe, regulating valves are a type of valve used to control the flow. Regulating valves can be considered control valves. Control valves also control fluid flow, hence their name.
Regulating valves are operated and controlled automatically using pressure difference. An actuator is used to actuate valves in order to turn them one way or another. There are many types of actuators, such as hydraulic actuators, pneumatic actuators, mechanical actuators, and more. Actuation is the process of actuating a valve.
There are many types of valves that are regulating valves:
Check valve
Pressure relief valve
Pressure regulating valve
Check Valve
A check valve opens with forward flow and closes against reverse flow to act as a safety device for fluid to flow in only one direction. Check valves are generally installed to prevent backflow. Backflow is when water flows backward in the supply line due to pressure changes.
Check valves require a minimum pressure difference between inlet and outlet to open the valve and allow fluid flow through it. If there is minimum pressure difference or inlet pressure becomes equal to outlet pressure, then the check valve opens. If the inlet pressure starts to fall due to damage to parts, then the check valve will close automatically. Depending on the check valve design, the closing mechanism can change.
Pressure Relief Valve
Pressure relief valves are spring-loaded safety valves. Pressure relief valves are normally closed but are opened automatically when the safe pressure limit is crossed. The safe pressure limit is the pressure at which the valve should be operated.
We release the pressure to protect the system from high pressure damage. That is why the outlet of the pressure relief valve is connected to the tank. This ensures pressure does not build up in the system.
Similar to the spring in a pressure cooker whistle, there is a spring inside the pressure relief valve. This spring is present in the middle of the valve, also called the bonnet. The spring helps to actuate the valve depending upon the pressure.
The safe pressure limit of the pressure relief valve can be changed by adjusting spring tension. An adjustment screw is used to set the pressure of the relief valve. As you loosen or tighten the screw, the tension in the spring is adjusted. This will increase or decrease the set pressure.
In pipes, if the fluid reaches pressure higher than set limit, then the fluid pushes the disc upwards. This pushes the spring attached to the disc. The spring gets compressed and disc is moved upwards to open the valve.
If the fluid pressure from inlet is reduced below set limit, the spring tries to come to its original position. This is because spring force becomes greater than fluid pressure. This causes the disc to come down and close the valve.
Pressure Regulating Valve
Pressure regulating valves are also known as pressure reducing valve. It is normally an open type valve that maintains a constant pressure in the pipeline even when there are fluctuations in the inlet and outlet pressure.
Pressure regulating valves consist of the following elements:
Poppet valve
Spring
Sensing element such as a diaphragm or a piston
As the outlet pressure increases, approaching the set pressure of poppet valve, the fluid is diverted over the diaphragm. The fluid pressure under the diaphragm begins to overcome spring pressure. This forces the poppet valve upward and closes the valve.
When the outlet pressure drops below the set point of the valve, the spring pressure overcomes the outlet pressure. This forces the valve downward, opening the valve.
As pressure in the inlet side becomes more than set pressure, the fluid enters on the top of the poppet and closes the valve. The valve remains closed until inlet pressure becomes equal to outlet pressure.
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FAQs
What is a valve?
A valve is a device used to control the flow of a fluid in a pipeline. It can either stop, regulate, or start the flow of liquid or gas, depending on the type and application. Valves can be operated manually or automatically using actuators.
What is the function of a shut-off valve?
Shut-off valves start or stop the flow of fluid in a pipe. These valves can be operated manually or automatically through an actuator. Common shut-off valves include the ball valve, gate valve, globe valve, and butterfly valve.
What is a gate valve used for?
A gate valve insert a rectangular wedge into the path of a flowing fluid. It is a multi-turn valve, meaning it requires several turns to open or close fully. These valves are used where frequent opening and closing are not required.
What is the difference between a globe valve and a gate valve?
A globe valve can regulate the flow of fluid, unlike a gate valve that is only used stop or start the flow. The globe valve uses a disc that moves vertically to control the space between the disc and seat, allowing gradual control of the fluid flow.
How does a butterfly valve function?
A butterfly valve is a quarter-turn valve used to shut off or start fluid flow. It uses a disc that rotates 90° to block or allow fluid flow through the pipes. Butterfly valves are ideal for quick-acting applications due to their simple design.
What is a check valve?
A check valve allows fluid to flow in one direction and prevents backflow. It opens when the fluid flows in the correct direction and automatically closes if the flow reverses, acting as a safety feature in pipelines.
What is a control valve?
A control valve is a type of valve used to regulate the flow of fluid (liquid, gas, or slurry) in a system. Control valves automatically adjusts the flow rate, pressure, or temperature based on input signals from a control system, allowing for precise control over the process. Control valves are commonly used in industrial applications, such as chemical plants, water treatment facilities, and HVAC systems, to ensure optimal performance and safety.
How does a control valve work?
Control valves use a combination of a valve body, actuator, and sensor to regulate fluid flow. The actuator (which can be pneumatic, hydraulic, or electric) adjusts the position of the valve's internal components (such as a disc, ball, or plug) based on signals from a control system. These signals, often from a pressure or temperature sensor, tell the actuator to open or close the valve to maintain the desired flow rate, pressure, or temperature.
What is a plug valve?
A plug valve is a type of valve that controls the flow of fluid by using a cylindrical or tapered plug that can be rotated to open or close the flow path. The plug has one or more holes (ports) that align with the pipe's flow path when the valve is open. Plug valves are typically used for on/off or diversion applications and can handle both liquids and gases.
How does a plug valve work?
A plug valve operates by rotating a cylindrical or tapered plug inside the valve body. The plug has one or more ports that line up with the inlet and outlet ports of the valve when it is turned to the open position, allowing fluid to pass through. When the valve is closed, the ports are rotated away from the flow path, stopping the fluid from passing through. The operation is typically manual, but can also be automated with an actuator.
What is the purpose of a pressure relief valve?
A pressure relief valve is used to prevent excessive pressure buildup in a system. It opens automatically when the pressure exceeds a safe limit, allowing the fluid to escape and protecting the system from damage.
How does a pressure regulating valve work?
A pressure regulating valve maintains a constant pressure in the pipeline, regardless of pressure fluctuations at the inlet or outlet. It automatically adjusts to maintain the set pressure by controlling the flow of fluid.
What is an actuator in a valve?
An actuator is a device that automatically operates a valve. It uses an external control like pressure difference, electric motors, or hydraulic systems to open or close the valve without manual intervention. Common types of actuators include pneumatic actuators and hydraulic actuators.
Why would I need to use a ball valve over a globe valve?
A ball valve is ideal for applications where quick shutoff is needed, with only a 90° turn required to close. On the other hand, a globe valve is better suited for regulating flow, as it provides finer control over the flow rate.
Can a valve be operated automatically?
Yes, many valves, especially shut-off valves, can be operated automatically using actuators. These actuators use a pressure difference or other control systems to open or close the valve without human intervention.
What is a flanged valve?
A flanged valve is a type of valve that has flanges on either side, which are used to connect the valve to a pipeline. The flanges are typically bolted together, ensuring a tight seal and preventing leaks. These valves are often used in systems that handle high-pressure or high-temperature fluids.
Quiz
Question #1: What is the primary function of a valve?
To increase the flow of fluid
To decrease or stop the flow of fluid
To monitor the pressure of fluid
To regulate the temperature of fluid
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Question #2: Which valve type is commonly used for quick on/off flow control and can operate with a 90° turn?
Gate valve
Plug valve
Ball valve
Globe valve
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Question #3: Which valve type uses a tapered or cylindrical plug to control the flow of fluid?
Gate valve
Plug valve
Ball valve
Butterfly valve
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Question #4: Which of the following valves is specifically used for regulating flow and pressure in a pipeline?
Check valve
Gate valve
Pressure relief valve
Butterfly valve
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Question #5: Which type of valve is designed to prevent backflow in a system?
Pressure relief valve
Check valve
Globe valve
Ball valve
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