What is Pinch Valve?
A pinch valve is a full bore or fully ported type of control valve which uses a pinching effect to obstruct fluid flow.
A pinch valve is a 2/2-way valve designed to shut off or control the flow of corrosive, abrasive or granular media. It utilizes pressurized air to open or close the valve. In the open position, the valve has no restrictions and allows a wide range of media to pass through the bore.
The flexible internal rubber sleeve in the valve keeps the media isolated preventing the risk of contamination. Pinch valves are ideally suited for use with slurries and granular products like sand, cement, gravel, textile fiber, carbon, powder, pellets, chipping, glass fragments, etc. These valves are cost-effective, reliable, and easy to use, making them desirable in a wide range of industrial applications.
Pinch valves employ an elastic tubing (sleeve/hose) and a device that directly contacts the tubing (body). Forcing the tubing together will create a seal that is equivalent to the tubing’s permeability.
Air-operated pinch valves consist of an elasticized reinforced rubber hose, a type of housing, and two-socket end covers (or flanges). In air-operated pinch valves, the rubber hoses are usually press-fitted and centered into the housing ends by the socket covers.
There is no additional actuator, the valve closes as soon as there is a pressurized air supply into the body. When the air supply becomes interrupted and the volume of air exhausts, the elastic rubber hose starts to open due to the force of the process flow.
How does a pinch valve work?
A pinch valve consists of three major components: housing, an internal rubber sleeve, and end connections. The rubber sleeve is fitted into the housing from inlet to outlet and is the only component that comes in contact with the media.
The end connections are bolted, screwed, or threaded at each end to provide support and connection to the valve. When the pressurized air is applied to the valve, it pushes down the rubber sleeve, creating a pinching effect. When the rubber sleeve is completely pinched, the flow is obstructed, and the valve is closed.
Unlike the conventional valves like ball or gate valves where particles can get trapped around the ball or discs, the rubber sleeve in a pinch valve is able to trap the particles around it, providing an excellent shut-off.
When the external air pressure is no longer applied to the rubber sleeve, the elastic rebounding property of it along with the force of the flowing media fully opens the valve. The fully opened valve provides free flow passage to the media preventing the valve from clogging or blockage.
The media also only comes into contact with the rubber sleeve, allowing the media to be isolated, no contamination, and no damage to any other components. When the abrasive media strikes the rubber sleeve, it absorbs the impact and deflects it back to the media. This resilient property helps the rubber sleeve wear at a much slower rate and gives it a longer service life than metal surfaces.
What are the types of pinch valve?
1. Clamp valve
This type of pinch valve has a flexible tube or clamp, the flexible tube has a heat-shrunk reinforcing jacket that is made from fluorocarbon resin. The clamping mechanism consists of a compressor that travels down a stem with the rotation of a hand-wheel or power operator, and a yoke that travels up the steam at the same time.
2. Air operated pinch valves
By using air operated pinch valve, we could get complete and true full bore, and they are also able to do the tight shut off even on solids such as granules, pellets, and any types of slurries. Air operated pinch valves works without any wear of the elastic rubber hose because the kinetic energy of the solids is absorbed through the extremely high elasticity of the rubber
How does a pinch valve can self-clean?
Inside a pinch valve, there is a rubber tube or sleeve that is pinched by steel bars on the centerline of the valve to close it. To close the pinch valve, the rubber sleeve which is full bore will begin to stretch. As it begins to stretch the material or scale buildup begins to flake.
So, when the sleeve continues to close the valve, the flaking increases, but the fluid velocity also increases substantially. Therefore, the flaked material/scale is blasted with higher velocity flow from the elastic surface of the rubber sleeve.
Application of Pinch Valve
Pinch valves are typically used in applications where the media needs to be completely isolated from any internal valve parts. The sleeve will contain the flow media and isolate it from the environment hence reducing contamination. They are commonly applied to medical instruments, clinical or chemical analyzers, and a wide range of laboratory equipment.
Pinch valves are also used for slurries or processes with entrained solids because the flexible rubber sleeve closes drop tight around solids. This avoids entrapment by the seat or in crevices, which would happen if using a globe, diaphragm, butterfly, gate, or ball valves.
Major industries that use pinch valves are:
- Bulk and solids handling,
- Cement industry,
- Waste water industry,
- Chemical industry,
- Food industry,
- Beverage industry,
- Ceramic-/Glass-/Plastic industry.
Advantages of Pinch Valve
- Low & easy maintenance
- Low weight
- No clogging or dead spots
- Compact, simple, robust & straight through design
- Very fast opening/closing times
- Less air consumption
- Permanent seal with tight shutoff
- Minimal turbulence & friction
- No mechanical parts, and no bearings, seals or packing required.
- Only one replaceable part (elastomer sleeve)
- No extra or special actuator required
- Inexpensive with extremely good Total Cost of Ownership.
Disadvantages of Pinch Valve
- Temperature range is limited
- Medium operating pressure is limited
- Face to face length may be an issue when limited space for fitting the valve is available.