The valves are used all over the world for controlling the flow of fluids. They are used to control different types of fluids. There are multiple types of valves, and a diaphragm valve is one of them. Diaphragm valves are used for closing, opening, and throttling the fluid flow. This article mainly explains diaphragm valve working, types, parts, and many other aspects.
What is a Diaphragm Valve?
A diaphragm valve is a type of valve that uses a flexible diaphragm to regulate the flow of fluid. The diaphragm valve is also known as a membrane valve.
The diaphragm or membrane is a flexible pressure-responsive part. This part delivers force to regulate, shut, or open the valve. This type of valve is very similar to a pinch valve, but it uses an elastic membrane instead of a flexible liner to isolate the fluid flow from the closure part.
The diaphragm valves have two types:
- Weir valve
- Straight-way valve
The weir valve is the most commonly used diaphragm valve. The linear or straight-way valve needs the additional expansion of the diaphragm, which reduces the service life of the diaphragm. Therefore, a straight-way valve is less common than a weir valve.
The main advantage of the diaphragm valve is that you can isolate the valve parts from the working fluid. This structure also doesn’t need stuffing box seals (packings) to stop fluid leaks as you use in other types of valves.
The diaphragm of the valve connects with a compressor via bolts molded into the diaphragm.
This compressor moves the stem of the valve in upward and downward directions. Therefore, the diaphragm moves up and down with the up and down movement of the compressor.
These types of valves may also be employed for throttle services. The weir-type valve has good throttling, but the range is limited. Due to the large closing area along with the valve seat, the throttling behavior essentially corresponds to that of a quick-opening valve.
Diaphragm Valve Working
A diaphragm valve uses a ‘pinching’ method to regulate the fluid flow through the valve. The diaphragm connects with a compressor. This compressor further connects with the stem.
When the valve operator desires to increase the fluid flow rate, he moves the stem upward. As the stem moves up, it further moves the compressor in an upward direction. This compressor further transfers its motion to the connected diaphragm, and the diaphragm also starts moving upward.
As the diaphragm moves up, the fluid flow increases according to the operator’s requirements.
When the operator wants to lower or close the fluid flow, he turns the stem and moves it downward. This stem transfers its motion to the compressor, which further presses the diaphragm in a downward direction and reduces or closes the flow.
Some valves also have throttling fluid flows. In such a case, the diaphragm is partially closed and partially opened.
To better understand the working of the diaphragm valve, watch the following video:
Read Also: Working of Check Valve
Types of Diaphragm Valves
The diaphragm valve has the following types:
- Weir valve
- Straight-way valve
1) Weir Diaphragm Valve
This is one of the most famous types of diaphragm valve. This design is ideal for small, leak-free flow controls due to the bonnet on the actuator and diaphragm.
The inclined body design of this valve provides a unique self-draining feature, and this draining can occur in both directions of the valve. Therefore, it is not best for some specific applications.
These valves are best suitable for corrosive or hazardous gases and liquids because the valve bonnet controls diaphragm failure or any leakage by the valve.
Weir valves are primarily used for homogeneous, clean liquids because viscous sludge and contaminations can collect on the saddle’s side. These are most commonly used in applications such as water, corrosive, gas production, chemicals, and food applications.
2) Straight-way Diaphragm Valve
The straight-way or in-line valve has an identical structure as the weir-type, but it has a completely straight pathway instead of the characteristic saddle.
These valves have more flexible diaphragms. These diaphragms make contact with the valve bottom, which can increase the diaphragm travel distance. Due to the flexibility of the diaphragm, these valves generally have a shorter life cycle than the weir structure and require frequent repairs/replacements.
The in-line or straight-way diaphragm valves are used for viscous liquids, water sludge, and other applications where you want to reduce the clogging. It’s also useful for bidirectional flow ranges as there is no saddle to prevent quick changes from inlet to outlet.
Read Also: Working of Ball Valve
Additional Diaphragm Valve Types
- Process valve: These are the most common mechanical diaphragms designed to stop, start, or regulate a fluid flow.
- Diaphragm actuated gate valves: It is a bi-directional flow safety valve. It uses a combine method of the gate valve and diaphragm valve to produce a very reliable hybrid.
- Sanitary diaphragm valves: It helps to stop fluid contamination. Sterile materials are used for the construction of these diaphragm valves. They have the ability to foster a sterilized atmosphere.
- Zero static valves: This valve is best suitable for clean operational applications because it has the capability to remove the flow stagnation and bacterial growth opportunities.
- Shut-off valves: This is a most common type of valve which uses a positive closure to stop the fluid flow.
- Diaphragm Solenoid Valve: This is a type of the regular solenoid valve, which is an electromechanical valve employed to control flow. In addition to the solenoid coil, this valve also has a rubber diaphragm in the valve body. It opens and closes against the hard seat. It can act indirectly or directly.
- Indirectly acting diaphragm solenoid valves: It is also called a pilot solenoid valve. It requires pressure on the diaphragm to operate. When the liquid flowing by the valve gets adequate pressure, the position of the diaphragm changes. In simple words, the pressure of the fluid behaves as a pilot to direct the position of the diaphragm.
- Direct-acting diaphragm solenoid valves: As the solenoid coil starts working, the direct-acting solenoid diaphragm valve changes the position of the diaphragm. The membrane opens and shuts depending on whether the valve is normally shut or normally opened.
Parts of Diaphragm Valve
The diaphragm valve has the following major components:
- Stem
- Compressor
- Bonnet
- Actuator
1) Stem
The valve stem may be non-indicating or indicating. If this stem is non-indicating, the handwheel rotates the valve stem bushing to engage the stem threads. This engagement helps to move the compressor connected to the stem upward and downward and connects the diaphragm to the compressor. The non-indicating stem uses seal bushing with sealed bonnets.
The indicating stem has a similar design as that of the non-indicating stem, but it has a longer stem stretched upwards through the handwheel. The indicating body uses a sealing bonnet with O-ring and sealed a bushing.
2) Compressor
The compressor is a most important part of the diaphragm valve. It uses to operate the diaphragm. One end of the compressor connects with the stem, while the other end connects with the diaphragm.
As you turn the handwheel to move the stem up or down, the stem transfers its motion to the compressor. As the compressor receives motion, it forces the diaphragm to move upward or downward to regulate the fluid flow according to your requirements.
Read Also: Different types of Compressors
3) Bonnet
It acts as housing on top of the valve and contains the non-wetted parts of the valve, such as the compressor, stem, and handwheel mechanism. It is screwed with the valve body.
The bonnet of the diaphragm valve is operated by a lever. It has a quick opening nature. In the case of conventional weir-type, these bonnets can be replaced by the standard bonnet.
By using bonnets with a maximum size of 10 cm, the diaphragm valve can be employed for vacuum operation. With large valves, you will need to use a vacuum-tight bonnet.
4) Actuator
This part of the valve uses to operate the stem, which further opens or closes the valve disc to regulate the fluid flow. Different types of actuators are used according to the requirements of the applications, such as required torque, automatic, and speed requirements for valve operation.
Various actuators perform different functions such as positioners, valve position electric relays, and adjustable orifices for precise flow control.
Read Also: Working of Butterfly Valve
Methods Of Flow Control
The diaphragm valve has a flexible membrane coupled with the compressor via a bolt molded into the diaphragm. Instead of compressing and closing the liner, the compressor pushes the diaphragm in the downward direction to make contact with the body’s bottom side to stop the fluid flow.
The manual diaphragm valve controls the pressure drop across the valve and offers a variable and precise degree of opening. Therefore, this is one of the best valves for flow control.
This type of valve has a handwheel. The operator turns the handwheel until the required amount of fluid flows by the system.
For fluid flow opening and closing applications, the handwheel uses to move the compressor up and down. As the handwheel turns, the compressor pushes the diaphragm towards the bottom body of the valve and stops the flow or lifts it upward until the desired amount of fluid flows by the system.
Construction materials of Diaphragm Valves
Different types of materials are used for the construction of the diaphragm valves. The selection of material depends on the properties of the material, such as efficiency, operational frequency, pressure, and temperature.
The diaphragm made of elastic material has excellent chemical resistance at high temperatures. However, the mechanical characteristics of elastic materials reduce at high temperatures (i.e., more than 150°F) and high pressure. The concentration of the medium that a diaphragm can control is another factor that influences the functionality of the diaphragm.
Following are some famous materials used for the construction of the diaphragm valve:
1) Diaphragm Materials
- Rubber lined or Unlined type: Viton, Leather, Silicone rubber, Natural Rubber, Buna – N or Nitrile.
- Fluorine Plastic Type: PFA EPDM backing, PTFE with EPDM backing, or FEP with EPDM backing.
2) Valve Body Materials
- Wood
- Brass
- Plastic: Polyvinylidene fluoride, Polyethylene, Polypropylene, Polyvinylchloride, Acrylonitrile butadiene styrene.
- Steel: Carbon steel, Stainless steel, Cast iron, Ductile iron, and Alloy 20.
Read Also: Different types of Valves
Types of Diaphragm Valve Connections
Diaphragm valves are attached to various piping systems. The connection type of the valve varies according to the requirements of the pre-existing system and the required type of seal. There are multiple types of connections, and some of them are given below:
- Threaded: The ends of the threaded valve contain inner or outer thread that allows the pipe to be screwed over or into the end of the valve. The threaded design is one of the simplest and most common design of the diaphragm valve.
- Metal surface seal: The metal surface seal uses a metal gasket between two fitting sections. The gasket makes face seals on both sides of the fittings.
- Compression fittings: This fitting has the capacity to seal pipe connections without threading or welding. The seal is produced as you tighten the nut, and the washer is compressed around the 2nd pipe to generate a tight seal.
- Socket welding/soldering: The socket weld connection between the two parts is soldered and difficult to lose.
- Butt welding: This welding fixes a butt joint. This butt joint is positioned between two sections, bars, or plates. In this way, a butt joint connects two parts without interlocking or
- Bolt Flanges: This type of connection uses at the valve outlet or inlet.
- Tube Fitting: It enables direct connection from the pipeline to the valve.
- Clamp Flange: This is a spring hinge flange wrapped around a pipe for connection.
Applications of Diaphragm Valves
- The diaphragm valves are used in corrosive applications.
- These use for the regulation of dirty or clean air and water services.
- These types of valves are used in the power industries.
- They use in de-mineralized water systems.
- The diaphragm valve uses in the water treatment system.
- They use in chemical and food processing systems.
- They use in vacuum services.
- They use in pharmaceutical manufacturing systems.
Advantages and Disadvantages of Diaphragm Valves
Advantages of Diaphragm Valve
- You can use them for both throttling and on-off flow applications.
- It has many linings due to that; it provides good chemical resistance.
- There are no stem leakage issues.
- It delivers bubble-tight service.
- These valves don’t contain pockets for trapping contaminations.
- These are the best choice for viscous and slurries fluids.
- The diaphragm valve is the best choice for radioactive fluids and hazardous chemicals.
- They don’t allow impurities in the fluid flow. Therefore, they are most commonly employed in brewing, pharmaceutical, food processing, and other applications.
Disadvantages of Diaphragm Valve
- The weir of the valve can stop the complete drainage of piping.
- The body of this valve must be made of corrosion-resistant material.
- This type of valve is not suitable for very high-pressure applications (more than 300 psi).
- The diaphragm can corrode when it is most widely used for heavy throttling services with contamination.
- It only works efficiently at moderate pressure (up to 300 psi).
- These valves are not best suitable for multi-turn operations.
- You can use it only for moderate temperature (up to 400 F) applications.
- It may limit the hydrostatic pressure.
Differnce between Diaphragm Valve and Pinch Valve
| Diaphragm Valve | Pinch Valve |
|---|---|
| It uses a rubber diaphragm to control the fluid flow. | It uses a rubber sleeve to control the fluid flow. |
| It is less reliable. | The pinch valve is more reliable than the diaphragm valve. |
| These valves have less service life than the diaphragm valves. | These have a long service life. |
| It can’t stop the fluid flow immediately. It takes some time to fully close the fluid flow. | The pinch valve has the capability to quickly stop the fluid flow. |
FAQ Section
What is a diaphragm valve used for?
The main function of the diaphragm valve is to regulate the flow of different fluids. These valves use a rubber diaphragm to control the fluid flow. This diaphragm moves upward and downward to close or open the fluid flow.
What is another name for the diaphragm valve?
The diaphragm valve is also known as a membrane valve. It uses a rubber membrane or diaphragm to control the fluid flow.
What are the types of diaphragm valves?
The diaphragm valves have the following major types:
- Straight-way valve
- Weir valve
- Diaphragm actuated gate valves
- Sanitary diaphragm valves
- Zero static valves
Which is the most common material for diaphragm?
EPDM is a most popular material used for the construction of diaphragms.
It has excellent chemical resistance to many corrosive elements such as hot water, caustic alkalis, and acids.
