Pinch Valves vs. Traditional Valves
“Five Must-Know Reasons for Success with Pinch Valves”

Are you wondering why to use AKO pinch valves instead of the conventional ball valve, butterfly or plug valve? If you want practical solutions to control corrosive and viscous fluids, abrasive granules, powders and slurries in pipelines the cost effective, low maintenance pinch valve is ideally suited for a variety of applications and industries and many times will outperform other types of valves year-round.

Unlike the conventional ball valve or butterfly valve the AKO pinch valve features full bore straight through flow, free passage of solids, negligible headloss and full shut-off, even with suspended solids in the product stream. For these reasons pinch valves are the most practical solution for all kinds of ON/OFF or flow control applications including abrasive, corrosive and fibrous products, granules, powders and slurries.

Are pinch valves the right choice for you?

You may have found out about pinch valves by chance or maybe, by keyword search on the Internet for valves in general or pinch valves in particular, or maybe someone recommended you consider them or you’re responding to an ad you saw. It doesn’t matter how or why you inquired. Now, that you have made contact, we are glad to meet you and are going to do our best to provide you with the information you are looking for so that you have the right facts to make your selection.

How can we help you best?

• Perhaps you are looking for a valve for a tough shut-off or flow control application?
• Are you concerned about suspended solids, fibers or granules in the product stream
  that may cause plugging of conventional ball or plug valves?
• Or, are you looking for a fairly inexpensive valve that has no obstructions in the valve
  flow path giving you a high flow coefficient (Cv)?

All of the above mentioned concerns and many more are taken care of when you consider AKO pinch valves for your application.

Pinch valves are probably the most versatile valves you can use when you have to deal with harsh and highly abrasive flow control situations including slurries, sludges and even pneumatic conveying systems. In fact, any product that can flow through a pipeline is fair game.

A pinch valve is made up of only a few parts, with the flexible sleeve probably being the most important item. Enclosed and surrounded by the valve body, the pinch valve sleeve is firmly held in place between the two ends of the valve body and by introducing compressed air or a suitable liquid between the valve body and the sleeve, the valve can be fully closed or “pinched off”. When the external pressure on the sleeve is released the sleeve will again spring back to its original fully open position.

Most likely you have experienced how a pinch valve works when you pinched a garden hose to control water flow or used a pinch cock on rubber tubing in the laboratory. The industrial version of a pinch valve is based on the same principle of restricting or controlling flow of liquids, slurries or granules, however, with a number of special design considerations added to match and adapt the industrial pinch valve to a multitude of field conditions.

What to look for when specifying Pinch Valves

For many years it was felt that “any pinch valve was just a pinch valve” and that all were created equal. Of course, experience has proven that no two applications are the same and where one application would be a success different operating conditions required different solutions.

1. Pinch valve sleeve integrity
Starting with the pinch valve sleeve, the choice of material is most important and compatibility of sleeve material and product is the basis for long and trouble-free valve operation. One of the key features of a good pinch valve sleeve is maintaining full bore straight through flow when open. If the sleeve material is not sufficiently flexible it will develop a permanent “set” and will no longer open fully when closing pressure is released. The walls of the sleeve protrude into the product stream and generate increased pressure drop and unnecessary turbulence. In addition, with slurries or abrasive granules as the product stream the increased abrasion causes rapid wear of the sleeve walls. As a result the sleeves wear out prematurely and have to be replaced more frequently with resulting increase in downtime (production interruptions) and maintenance costs.

2. Easy fit between flanges
Pinch valves should be designed so that they fit easily between flanges of the connecting piping without having to add extra space needed for compression of flanged sleeves when the valve has to be removed for service. The valve design shall be such that the sleeve is completely contained between the end connections of the valve housing, making removal and insertion into the pipeline possible without having to loosen adjacent pipe supports for clearance. This also allows for consistent standard torquing of flange connections without having to be dependent on the resiliency of the sleeve’s rubber flange to achieve proper sealing. See Fig.1 above.

3. Flange material selection
When material compatibility or contamination with the product are a factor in the application, all wetted surfaces of the pinch valve must be considered safe. Therefore, where sleeves have a simple cylindrical shape and have no flanges on either end the end flanges of the valve housing should be available in the appropriate material or should be available with a flange liner for compatibility.

4. Body material and design
The pinch valve body or housing, especially for larger diameter valves, should be available in a light material, such as aluminum, to make it easier to handle the valve. Since the housing normally does not come in contact with the product it is not necessary that the housing material is compatible with the product as long as the surfaces of the housing have a suitable protective coating against surrounding elements. The volume of the annular space between the housing walls and the sleeve determines the volume of compressed air or liquid required to close the valve and the smaller this volume is the less fluid exchange is necessary and the less energy is expended during cycling. In addition, smaller housings also save on weight and make the valves easier to handle, saving cost of transport and installation.

5. Choice of sleeve material
For a successful selection of a pinch valve for your specific application you should be able to select the optimum material from a variety of choices for maximum compatibility with the product to be handled. While the housing material for each valve can be the same, the sleeve material and construction will determine to a great extent how successful the application will be. Factors such as product temperature, pressure and chemical properties may allow a sleeve from plain natural abrasion resistant rubber while higher temperatures may require special elastomers such as silicone. Of course, when it comes to specific industries pinch valve sleeves made from food grade elastomers may be required and should be an option.
A summary of elastomer materials normally available for standard AKO sleeves includes
Neoprene®, Natural rubber, EPDM, Viton®, Silicone, Nitrile, Hypalon® and Butyl. When required, food grade materials are also available.

6. Controls and technical assistance
Finally, even though with pinch valves you have only one moving part to be concerned about - the sleeve - and it can be either open or closed or, if used as a flow control device, somewhere in-between, you should be able to avail yourself of technical assistance from the supplier to install the appropriate control devices for the correct operation of the valve.

Fully open and fully closed is straight forward and requires only normally closed or normally open solenoid control valves. However, pinch valves in series (with mechanical or pneumatic control), vacuum applications, or when fail-safe installations are required control schemes become more involved and may require special considerations.