control valve

What is a pinch valve and how does it work

What is a pinch valve

Pinch valves are similar to diaphragm valves, in pinch valves, the body is provided with sleeves, which get squeezed to control or stop the flow. The sleeve could be of corrosion-resistant materials such as rubber or PTFE. Cast iron is used to manufacture the body. Pinch valves are lower in cost and have a simple design. These valves shut off the flow by pinching and sealing off a synthetic or natural rubber tube. The operating mechanism of the pinch valve is separated from the fluid, so it can be used where corrosion and contamination fluid is a problem.

Pinch valves are used for special purposes where service pressures are very low, they are used in the chemical process industry. Recently developed pinch valves can withstand higher pressure and temperature and they can be used for mining and mineral industry.

How does a pinch valve work

Pinch valves can be considered as an elastomer tube, that is fitted into a frame or a fabricated metal body. The closing action is simply by cutting the flow. It uses a rigid bar to press against a flexible element such as a diaphragm or a rubber tube to pinch off the flow. The working element of pinch valves is known as a clamp valve, it is an elastomeric tube or sleeve which can be squeezed at its mid-section by some mechanical system till the flow path closure. Pinch valves usually employ a device that directly contacts process tubing. These valves can be easily engineered as tight shut off valves, the valve is often supplied with pinch tube contained within an outer-pipe between the end flanges. This would be helpful to monitor tube leaks and provides a degree of secondary containment. These valves are completely cavity-free and are suited for isolating pipelines that carry abrasive slurries and large suspended solids.
In the open state, the valve bolted between pipe flanges, transmits fluids just as it were part of the piping. When the compressed air enters the valve body, it pinches the tube into an oval shape at the center and finally shuts off the flow at the center and then shuts off the flow completely. All pinch valves close over along the contact area so that the seating surface can envelop even large objects without leaking or being cut. Once suitable sleeve material is selected then the valve can work with a variety of fluids. These valves can be used for food-grade applications because the fluid being carried does not come in contact with the metal surface.

What are the components in a pinch valve and how are they constructed

A pinch valve is a full bore or fully ported type of control valve, these valves use a pinching effect to obstruct the flow of fluids. The major components of pinch valves are body and sleeve. Pinch valves are capable of flow control application if the operating temperature is within the limit of the polymer. Stainless steel inlet and outlet connections are available and pneumatic cylinders actuate pinchers to pinch rubber sleeve to close the valve.

Pinch valve bodies are manufactured of synthetic or natural rubbers and plastics that have good abrasion resistance properties. All of these properties will help to protect the valve sleeve and provides virtually unimpeded flow. In most pinch valves the sleeves are exposed. There are other types of pinch valves that fully encloses the sleeve within a metallic body. Most exposed sleeve valves have limited vacuum applications because of the tendency of the sleeves to collapse when the vacuum is applied

What are the types of pinch valve

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 yoke which travels up the steam at the same time.

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 are 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.

What are the advantages of a pinch valve over isolation valves

  • The flow path won’t be obstructed and has less pressure drop
  • Resistant to damage from particulates in a fluid stream
  • Easy sterilization of fluid path
  • No dead volume inside the valve
  • Ease of changing the wetted surfaces between operations

What are the advantages of pinch valves

  • Ease of operation
  • Resistance to corrosion
  • Easy to repair
  • Low weight
  • Very fast opening and closing time
  • Self-cleaning and less air consumption
  • Permanent seal with tight shut-off
  • Minimal turbulence and friction
  • All pinch valves are capable to withstand the jamming or clogging that occurs with other valves
  • Straight flow path

What are the disadvantages of pinch valves

  • They are only capable of flow control when 50 percent is closed
  • They are big and bulky
  • Open body types can cause massive spillage when tube ruptures
  • Temperature range is limited
  • Medium operating pressure is limited
  • Face to face length could be an issue when limited space for fitting the valve is available.
  • Cannot be used with gas media

What are the applications of pinch valves

  • Cement industry
  • Wastewater industry
  • Chemical and food industry
  • Beverage industry
  • Ceramic, glass, and plastic industry

To get more info about the control valve check the following links

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