Pinch valves are a simple valve design that uses an elastomeric tube forced together or pinched to stop the flow of media. This force can be applied in a variety of ways: Compressed air or fluid can be supplied directly into the valve housing to force the elastomeric tubing closed or a clamp mechanism can be used that is forced closed, from a manual handle or an actuator.
Pinch valves are used in on/off applications as well as throttling services. The applications where this is useful range from clean or sanitary services such as the chemical, food and pharmaceutical industries to more industrial services such as wastewater, the cement industry and where there is flow of bulk solids. Pinch valves are used in sanitary services because of their cleanliness and drainage, while they are used in more industrial services because of their low friction and resistance to clogging. They do well in these services compared to other more common valve types such as butterfly, ball and globe valves because, along with their aforementioned merits, their simplicity makes them simple and cost-effective.
PINCH VALVE STYLES
The different types of pinch valves can be described broadly as two types: those where the sleeve is integral to the body and those where a separate clamp is used to pinch a tube or a hose closed.
INTEGRAL SLEEVE
The style of pinch valve that has an integral sleeve through the valve body can be actuated by compressed air or hydraulic pressure applied into the valve body between the body and sleeve. As the air or hydraulic pressure fills the body cavity, the pressure closes off the sleeve to restrict or stop the flow of media. These valves also may have a mechanism that is closed via a manual operator or actuator integral to the valve. This style of pinch valve can be used as a control valve when a machine is used to close the valve.
Pinch valves are generally very low maintenance. However, since they rely on an elastomeric tube or hose that is forced or clamped to restrict or stop the flow, the tube or hose is where the majority of the maintenance is required. When the sleeve, tube, or hose becomes worn or damaged from use, it must be replaced. Meanwhile, the valve body components, since they are isolated from valve media, require little maintenance.
Pinch valve components can be made from a variety of different materials depending on the severity of the service and the media that flows through the valve. The sleeve, tube, and hose can be made from neoprene, natural rubbers, silicone, EPDM (ethylene propylene diene monomer rubber, extremely durable synthetic rubber membrane that has a higher heat resistance than natural rubbers), FKM (fluoroelastomer, which has more heat and chemical resistance than nitrile or neoprene), and many other elastomers, while the body of the valve can be made from plastics, stainless steel, aluminum, and other metals depending on the service of the valve.
Integral sleeve-style pinch valves are chosen when the media can be corrosive or it contains solids or abrasives. This is because there is minimal friction within the sleeve of the pinch valve so it is resistant to clogging. These valves also may be chosen when minimal turbulence is required or in cases where excellent drainage is necessary. Pinch valves are also an excellent choice when media exposure to non-elastomeric materials can be an issue such as when the media is corrosive to metals.
CLAMP STYLE
The clamp style of the pinch valve essentially clamps a separate tube or hose closed with the use of a manual actuator, pneumatic actuator or solenoid actuator that exerts the clamping force to provide shutoff. This style of the pinch valve is completely separate from the tube or hose. It can be installed and removed from the system without disassembling the hose system or breaking the line. This type is designed for systems where breaks in the process tubing or hose are not feasible. These valves are used as a clamp for single-use tubing in most cases.
Since the clamp style of the pinch valve is separate from the tubing or hose that it closes off, the valve itself has very minimal maintenance. This style of the pinch valve is generally made from metallic materials such as stainless steel or aluminum, with handles made from plastics to help reduce weight. In some cases, this style of pinch valve can be made entirely from plastic to reduce cost and weight. However, doing so creates a more limited ability and life span.
Clamp-style pinch valves are chosen for services that require a valve that can be installed with no process break. They are generally installed on single-use disposable systems, in pharmaceutical manufacturing, and in food and beverage applications that use flexible or braided tubing.
CONCLUSION
Although pinch valves have a simple design and purpose, they are used for a wide variety of applications. Knowing their purpose and how they work allows those who choose them to pick the right type.
Source:www.valvemagazine.com/magazine/sections/features/10212-pinch-valves-an-uncomplicated-valve-with-an-important-purpose.html
