A pinch valve is one of the simplest valves. These valves have many advantages over conventional valves. Many other types of valves cannot control fluids with high solid concentrations because the solid particles jam the parts of the metal and clog the valve. Pinch valves are best suitable to process almost all fluids, even the most hazardous application conditions, without the use of mechanical or metal parts. This article explains the pinch valve working, parts, applications, and types.
What is a Pinch Valve?
A pinch valve is a flexible body valve with a flexible tube that can “pinch” together by mechanical or fluid pressure to close the fluid flow completely.
The pinch valve is also called a clamp valve or tube valve. This valve has a linear motion. A pinch valve is a 2/2-way valve made for controlling or blocking the flow of granular, abrasive, or corrosive fluids.
The pinch valves are used to stop, regulate and start the flow of fluids. These have a simple construction.
These types of valves have straight flow passages with no gaps or moving parts. The soft body of the valve can seal trapped solids. Due to this characteristic, this valve is best suitable for processing pharmaceuticals, food, and slurries.
Synthetic or natural rubber is used for the manufacturing of pinch tubes. In some cases, plastic is also used to make pinch tubes because plastic has excellent wear-resistant characteristics.
Maximum pinch valves have an open style which has an exposed pinch tube. There is another style in which a metal body completely surrounds the pinch tube.
The pinch valve has a lightweight and low maintenance cost than conventional valves. You can also use these valves in systems that require explosion-proof pipe plugs.
Pinch valves are best suitable for aseptic production lines and for applications where product purity is paramount, but the same designs have several drawbacks. The clamp or pinch valves have elastomeric bodies. Therefore, these aren’t ideal for applications where the fluid is transported at high temperatures. They are also not best for services or gases that require high-pressure flow.
How does a Pinch Valve work?
The pinch valve works on the pinch mechanism. This valve has the following three main parts:
- End connections
- Inner rubber boot
- Outer housing
The end connections are threaded, screwed, or bolted at both ends to offer connection and support to the valve.
The rubber sleeve is positioned inside the valve casing from the suction side to the discharge side. This is a unique part of the valve that makes a connection with the fluid.
As the high-pressure air exerts pressure on the valve, the air compresses the rubber sleeve in the downward direction and generates a pinching effect (as shown in the below-given Fig B). As the rubber sleeve is fully pressed, the fluid flow blocks and the valve closes.
The pinch valve’s rubber sleeve has the ability to trap contamination particles around it and provides an outstanding closing effect, unlike other types of valves such as gate valves and ball valves which can also trap particles around the disc or ball.
The pinch valve only opens when no force acts on it. As no external pressure is exerted on the rubber sleeve, its elastic resilience properties and the force of the flowing fluid cause the valve to open completely.
A fully open valve gives a free flow path for fluid to prevent the valve from blockage or clogging. Since the fluid only makes contact with the rubber sleeve, the fluid is isolated and doesn’t contaminate or damage any part of the valve.
Read Also: Working of Plug Valve
Methods of Flow Control
The pinch valve uses a linear motion control method as a diaphragm or membrane valve. This valve has a stem that has a free-wheel connection with a movable shut-off rod (known as a compressor). This compressor installs directly on the liner.
When the operator turns the handwheel, the compressor moves downward and forces the liner to move down. As the linear or rubber sleeve moves downward, it closes the valve and stops the fluid flow. The fluid pressure inside the valve helps to stop or start the flow.
Read Also: Different Types of Valves
Types of Pinch Valves
The pinch valve has the following types:
- NO Pinch Valve
- NC Valve
- CO Pinch Valve
1) Normally Open (NO) Pinch Valve
NO valve opens when there is no pressure on the valve rubber sleeve. As the pressurized air exerts pressure on the compressor, which is directly connected to a rubber sleeve, the compressor further compresses the rubber sleeve and stops the fluid flow.
These types of pinch valves are driven by two pressures:
- Positive control pressure force (air pressure)
- Operating pressure force (fluid pressure)
2) Normally Closed (NC) Pinch Valves
The normally closed pinch valve normally closes in non-pressurized conditions. It has a spring element.
A spring element carries out the valve shut-off process. This spring element pushes the pinch element for normal closure and stops the fluid flow. If there is vacuum pressure on the valve air vent and the spring force is exceeded, the rubber sleeve opens the flow path, and fluid begins to flow.
The following three forces drive the rubber sleeve of the NC valve:
- Spring force
- Control pressure force
- Operating pressure force
Read Also: Working and types of Check valve
3) Changeover (CO) Pinch Valve
The changeover valve is a combination of the normally closed valve and the normally open valve.
You can switch this valve between normally open or normally closed positions at any time by turning the changeover nut. The control pressure, operating pressure, and spring forces are the major forces that play a significant role in the valve opening and closing.
Parts of the Pinch Valve
The pinch valve has the following major parts:
- Stem
- Pinching device
- Body
- Rubber sleeve
- Handle
1) Body
Pinch valves are typically designed with a top compression pressure, letting thorough drainage in all positions except when inverted.
Furthermore, many of these valves feature a straight-through design, ensuring high flow rates with negligible turbulence. These characteristics contribute to low air consumption, minimizing the entry of airborne impurities and maintaining a relatively closed system.
2) Stem
The stem of the valve plays a crucial role in the valve’s operation as it facilitates the movement of the liner to open or close the valve. The stem is attached to the valve actuator, hand wheel, or lever through threading. By employing linear motion, the stem controls the motion of the disc to either stop or start the fluid flow.
3) Pinch Valve Actuator
To operate the disc and stem and control valve opening and closing, a valve actuator is employed. Pinch valves offer various types of actuators to suit different applications. Closure of pinch valves can be achieved manually or through fluid actuation.
How to Select a Pinch Valve?
The selection of the best pinch valve is the most critical step. There are multiple aspects that you must keep in mind for choosing a pinch valve.
Follow the below given major tips to select the best suitable pinch valve:
1) Valve Body Material
The material of the valve body must be light and easy to handle but does not have to be compatible with the fluid since they don’t make contact. However, the material for the rubber sleeve must be selected carefully because only this part of the valve makes contact with the fluid.
Different types of materials such as food-quality rubber, silicone, EPDM, NBR (nitrile), and natural rubber are used for the construction of the rubber sleeves. The material must have excellent wear resistance in order to stop environmental damage.
2) Certification
Some applications may require certification to ensure valve safety and clean media (e.g., drinking water, food-grade, etc.).
2) Temperature
During the valve selection, you must make sure that the valve material can resist the maximum and minimum working temperature requirements according to your application.
4) Pressure
The air pressure is a major factor that you must consider when choosing a pinch valve. The pressure of the flowing medium is called the operating pressure, and the air pressure used to generate the compression or pinch effect is called the control pressure.
To open the valve, the control pressure must be lower than the operating pressure, but the control pressure is typically 0 bar. If the pressure difference (pressure difference between operating and control pressures) is lower than the control pressure, the operating pressure can’t open the rubber sleeve.
If you want to shut off the valve, the operating pressure must be less than the control pressure. If the pressure difference is inadequate, the control pressure cannot overcome the operating pressure when the sleeve is pressed to shut off the valve.
What is the Symbol of the Pinch Valve?
The pinch valve has the following symbol:
How Does A Pinch Valve Can Self-Clean?
The pinch valve has a rubber sleeve. This sleeve is attached with a steel bar. The steel bar pinches the sleeve to close the valve. The rubber sleeve is fully bored into the valve.
For closing the valve, this rubber sleeve stretches completely. When it starts to stretch, the material accumulation will begin to flake.
Therefore, if the sleeve continuously closes the valve, flaking will increase, and the media velocity will also be increased significantly. As a result, the flaked material is thrown out of the sleeve’s elastic surface with the high-velocity flow.
Advantages and Disadvantages of Pinch Valves
Advantages of Pinch valve
- Pinch valves are ideal for corrosive or abrasive fluids.
- They don’t need an additional or special actuator.
- These have a straight flow path. Therefore, they don’t produce clogging or blocking for the flowing fluid.
- There is very low turbulence and friction.
- There is no need of packing, bearings, or seals.
- The pinch valve ensures a contamination-free fluid flow.
- It has easy maintenance.
- It has a self-cleaning capability.
- They consume less energy than other valves.
- These valves have low maintenance and repair costs.
- They have excellent sealing capabilities.
- They have a quick operation.
Disadvantages of Pinch Valve
- These valves are not ideal for high-temperature applications due to sleeve elasticity.
- In the event of a large pressure difference, the rubber sleeve may deform or squash, and the valve will not open completely.
- They are not ideal for vacuum services because the suction in the valve can cause sleeve damage.
- The operating pressure of the working media is limited.
Applications of Pinch Valves
Pinch valves are typically used in applications in which the medium must be completely separated from the internal component of the valve.
These types of valves are widely used in chemical analysis equipment, clinical, medical equipment, and various experimental equipment. The pinch valves are commonly used in slurry applications.
Some major industrial applications of the pinch valve are given below:
- Wastewater industry
- Plastic industry
- Ceramic industry
- Bulk and solid handling industry
- Cement industry
- Beverage and food industries
- Chemical industry
- Pharmaceutical industry
Pinch valve vs Gate valve
The main difference between pinch and gate valves is given below:
| Pinch Valve | Gate Valve |
|---|---|
| A pinch valve uses a rubber sleeve to control the fluid flow. | A gate valve uses a gate to regulate fluid flow. |
| It has a self-cleaning ability. | It needs manual cleaning. |
| This valve has fewer parts than the gate valve. | It has many parts. |
| It has a relatively low cost. | It has a high cost. |
| These valves have simple designs. | These have complex designs. |
Read Also: Working of Gate Valve
FAQ Section
What is the function of the Pinch Valve?
The pinch valves are used for closing, opening, and throttling applications. These valves have a straight-through design that permits unlimited flow, making them best suitable for open/close operations. Therefore, the pressure loss between the outlet and inlet is very low in these designs.
How does a pinch valve stop flow?
The pinch valve works on the pinch mechanism. It uses a compressor, rubber sleeve, and a handwheel to regulate the fluid flow. As the air pressure pinches or compresses the rubber sleeve, the rubber sleeve is pinched and stops the fluid flow.
Which motion can we observe in the pinch valve?
The pinch valve has linear motion. The pinch valves are used to throttle, stop and start the fluid flow via a system.
What are the parts of the Pinch valve?
- Compressor
- Handwheel
- Rubber sleeve or pipe
- Body
- Stem
What is Air Operated Pinch Valve?
A pinch valve that is operated through the pressure of air or natural gas is known as an air-operated valve.
What is a pinch valve used for?
The pinch valves are used to open, close, or control the flow of granular, abrasive, or corrosive fluids.
What is the difference between a solenoid valve and a pinch valve?
A pinch valve is a type of control valve that features a full bore or fully ported design. It utilizes a pinching effect to regulate the flow of fluids or gases by either closing or opening the passage. In the case of a solenoid pinch valve, it is an electronically controlled device that employs a solenoid to operate and control the opening and closing of tubes, thereby managing the flow of liquids or gases electronically.