Air operated pinch valves or mechanical pinch valves?

Which type of valve should I use and when?
This question can generally be answered with the aid of the following main criteria:

Which operating pressure is used in the application and does it require a fail-safe function?
Do you intend to use the installed pinch valve solely as an inlet valve or also as a control valve?
Once these issues have been clarified, it is usually possible to clearly identify which type of pinch valve you require.

1. The operating pressure in the application

The operating pressure in the relevant application is the most decisive criteria when selecting between mechanical pinch valves and air operated pinch valves.
Air operated pinch valves can normally only be used for operating pressures up to a maximum of 6 bar.
If your application has an operating pressure higher than 6 bar, a mechanical pinch valve is the only solution for you.
Naturally, mechanical pinch valves can also be used with operating pressures lower than 6 bar if desired.

Valve type Operating pressure < 6 bar Operating pressure > 6 bar
Air operated pinch valves Möglich Nicht möglich
Mechanical pinch valves Möglich Möglich

2. Fail-safe function

If your application requires a valve with a fail-safe function, a mechanical pinch valve with a single-acting pneumatic cylinder (spring closing) is usually the only option.
These valves are generally closed in their starting position (i.e. their non-operated state). In the event of a loss of the compressed air supply during operation, e.g. due to a power cut, our mechanical pinch valves close fully automatically and completely shut off the flow of the medium. The closing mechanism is triggered immediately and – depending on the nominal size of the armature – it takes a maximum of a few seconds until the entire valve is closed.

Air operated pinch valves could also be equipped with a fail-safe function and an additional compressed air supply tank and would thus be able to remain closed in the event of a loss of the compressed air supply – at least for a certain period of time. However, if the sleeve fitted in the air operated pinch valve becomes damaged or faulty (a crack or other leak), it would not be able to remain closed under any circumstances and the valve would no longer fulfil the requirements for a fail-safe function.

Valve type Fail-Safe Note
Air operated pinch valves Nicht Fail-Safe A normally closed state is possible by adding a fail-safe function & compressed air tank
Mechanical pinch valves Fail-Safe Only refers to pinch valves with a single-acting pneumatic cylinder (spring closing)

3. Inlet valve or control valve?

Air operated pinch valves are generally used for applications in which it is necessary to shut off the operating medium. Therefore, they primarily act as a simple inlet valve.
Although air operated pinch valves are also able to move to intermediate positions with the aid of a proportional pressure regulator valve, this will only enable you to roughly control the product flow. It is also important to note with this “rough” control of the valve using compressed air that the repeat accuracy of the control curve will not be repetitive.

Therefore, it is recommended that a mechanical pinch valve is used for applications that require precise control characteristics.
There are generally two possible alternatives suitable for this requirement:
The first option is a mechanical pinch valve with a double or single-acting pneumatic cylinder that controls the diameter of the pinch valve with the aid of an electro/pneumatic positioner.
An alternative to valves fitted with pneumatic drives are those fitted with so-called electric rotary drives that use an actuator control system to precisely control the mechanical pinch valves.

Valve type Intermediate positions Note
Air operated pinch valves ( Fail-Safe ) Rough control with the aid of a proportional pressure regulator valve
Mechanical pinch valves Fail-Safe  

Advantages & disadvantages of both types of valve

You will find a brief summary below of the features that will help you initially select which type of pinch valve would be best for you:

Air operated pinch valves

Advantages Disadvantages
Lower purchasing costs Maximum operating pressure of 6 bar
Lower inherent weight No precise control of the valve
Easier to maintain and repair No fail-safe function
Quicker response times (opening/closing) No mechanical or inductive position monitoring
Larger selection of valve connection options No forced opening
Larger selection of materials for all components  

Mechanical pinch valves

Advantages Disadvantages
Operating pressure up to 40 bar Higher purchasing costs
Precise control of the valve Higher weight & dimensions
Fail-safe function Slower response times (opening/closing)
Mechanical or inductive position monitoring  
Forced opening  

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