• SkillCat Team

A Complete Guide to Valves & their Uses

Updated: Jun 23

Piping: Chapter 8


Shut Off Valves


In this module, you will learn about:

What valve is, and

types of shut off valves Skip to quiz!


Valve


A valve is a device that it is used to decrease or stop the flow of a fluid. It is a type of fitting that controls the flow inside a pipeline.

The valve can be operated manually by turning the handle of the valve. Valves can also be operated by automatically using pressure difference and actuator. An actuator is a device that automatically controls the valve on or off.


The valves that use an actuator to operate automatically are called shut off valves. Regulating valves are operated automatically using pressure difference. Let us learn about shut off valve.


Shut Off Valves

A shut-off valve is used to start or stop the flow of fluid in the pipe. It works similar to an electric switch. An electric switch can be used to turn the system on or off. Similarly, to start or stop the fluid flow through the pipe, a shut-off valve is used.


A shut-off valve is 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.


The types of shut off valve are as follows:

  • Ball valve,

  • Gate valve, and

  • Globe valve

Ball Shut Off Valves


Ball valves are 2-way, 2-position valves that are used for shut-off or isolation of a system. The 2 ways are inlet and outlet of pipe. Open and close are the two positions for which ball valves are used.


Ball shut off valves can also be 3-way or 4-way. Such multi-port valves are used in applications 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 can use a 3 way shut-off valves.


A ball valve controls a liquid or gas flow using a rotary ball. The rotary ball has 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.


The ball shut-off valves have a fast shut-off with only a quarter-turn or 90° turn to close the valve. This makes them easier to use. They are used for application where frequent opening and closing is required.



Gate Shut Off Valves


Gate shut off valve is also used for starting or stopping flow. 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 to unscrew. This will result in vertical movement of the threaded rod or stem.

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.


For example, gate valves are used in power plants, mining, and water treatment applications.

Frequent closing and opening is not required in these applications.


Gate valves are easier to clean and maintain. This makes them suitable for application that involve slurries. For example, drainage pipeline of coal slurries.


Globe Shut Off 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 that are used for single inlet flow and outlet flow. When more than one inlet and single outlet, 3 way or 4 way globe valves is used.


In the globe valve, instead of a rectangular wedge, a disc is used to block the flow through the pipe. The other parts used such as stem, bonnet are similar to gate valve.

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. This gives 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 working of globe valve is similar to tap used in wash basin and kitchen. As you rotate the tap handle, fluid flow starts gradually, it will be maximum when the tap is fully opened.


In a globe valve, as you turn the handle, a disc is lowered or raised by means of the valve stem. When the disc is fully lowered, the fluid flow is shut off.


When the disc is fully raised, the fluid flow is at its maximum rate. If you turn the handle slightly, the disc is at less than maximum level. This will regulate the fluid flow with proportion to the vertical travel of the disc.


Globe valves are used for regulating and shut off applications in the following:

  • Swimming pool drain, and

  • Lubrication systems

All these systems require starting, stopping and regulating flow for its application.


For example, lubrication system used for drilling machine needs to be controlled. If the drilling is done at high speed more heat is produced, there we need more lubricant. For moderate or low speed drilling operation, we require less lubricant flow.


A valve is a device that it is used to decrease or stop the flow of a fluid. Shut off valves can be operated manually or automatically. Different types of shut off valves are:

  • Ball valve

  • Gate valve

  • Globe valve




Regulating Valves


In this module, we will learn about another type of valve that is a regulating valve. Skip to quiz!


Regulating Valves

Recall that a valve is used to start or stop the flow of a fluid. In addition to starting and stopping the flow inside the pipe, we also need to control the flow. A regulating valve is used to control the flow of fluid.


Recall that regulating valves are operated automatically using pressure difference. There is no requirement for any operator or external control.


The types of regulating valve are as follows:

  • Check valve,

  • Pressure release valve,

  • Pressure regulating valve, and

  • Backflow preventer valve


Check Valve


A check valve permits fluid to move in one direction. It opens with forward flow and closes against reverse flow. It acts as a safety device.

Check valves are generally installed in pipelines to prevent backflow. Backflow is when water flows backward in the supply line due to pressure changes. Such backflow can be prevented by a safety device such as a check valve.


A check valve requires 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 some accidental damage to parts, then the check valve will close automatically. Depending on the check valve design, the closing mechanism can change.


Check valves are very often used in HVAC systems. For example, an HVAC system is used in large buildings, where a coolant is pumped up. The check valves are installed here to make sure that the coolant is not flushing back down.


Pressure Release Valve


Pressure relief valves are spring-loaded safety valves. Pressure relief valves is normally closed. These valves open 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.


A pressure cooker has the whistle on top of it. The whistle has weight or spring inside. The whistle gets lifted if the pressure inside the cooker exceeds a limit.


As the whistle gets lifted, the steam gets released and the pressure inside the cooker come down. This release of pressure is done using a pressure relief valve.


Similar to the spring in the pressure cooker whistle, there is a spring inside the pressure relief valve. This spring is present in the middle of the valve, also called bonnet. The spring helps to actuate the valve depending upon the pressure.


The safe pressure limit of the pressure relief valve can be easily adjusted 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. It will close the valve.


Pressure Regulating Valve


Pressure regulating valve is also known as pressure reducing valve. It is normally open type valve. It maintains a constant pressure in the pipeline even when there are fluctuations in the inlet and outlet pressure.

Pressure regular consists 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 the pressure in the inlet side becomes more than the set pressure, the fluid enters on the top of the poppet. This pushes the spring loaded puppet to close the valve. The valve remains closed until inlet pressure becomes equal to outlet pressure.


Backflow Preventer Valve


A backflow preventer is a device that allows water to flow in one direction but never in the opposite direction. They rely on two one-way valves, or check valves, assembled in a series to prevent water from backing up into the supply line.

Water that enters a building’s fire protection, plumbing, or irrigation system from a main water supply line should only flow in one direction. But sometimes, pressure changes in the pipes can cause water to seep back into the main supply line. Backflow preventer valve is used to stop backflow of water in a pipe.


For example, irrigation system used for spraying water sprinklers is connected to main water supply line. If the pressure is dropped in the in the main supply line, the chemicals could go back and enter the main city drinking water system. When this happens, the public drinking water can be polluted.


Any time the pressure on the downstream side exceeds the pressure on the city side, the two check valves close. This prevents any backflow.


Regulating valves are operated automatically using pressure difference. Different types of regulating valves are:

  • Check valve,

  • Pressure release valve,

  • Pressure regulating valve, and

  • Backflow preventer valve




Question #1: Which of the following valve types requires only a 90 degree turn of the handle to fully open or close the valve?

  1. Ball Valve

  2. Gate Valve

  3. Both of the above

  4. None of these

Scroll down for the answer...











Answer: Ball Valve

The ball shut-off valves have a fast shut-off with only a quarter-turn or 90° turn to close the valve. This makes them easier to use.


Question #2: A globe valve is suitable for stopping and starting fluid flow, but not for regulating flow.

  1. True

  2. False

Scroll down for the answer...












Answer: False

A globe valve is used to stop, start and regulate flow.


Question #3: The valve which avoids back flow of water is_______.

  1. Gate valve

  2. Ball valve

  3. Globe valve

  4. Check valve

Scroll down for the answer...












Answer: Check valve

Check valve is a valve which permits fluid to move in one direction. It opens with forward flow and closes against back flow.





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