Looking at using pinch or diaphragm valve for a control valve application on dirty water containing abrasive material.  I have found products using both technologies, but I am *told* pinch valves do not have good controlability.  Can anyone offer advice for this application?

Sut-Flo and Red valve seem to be the names in pinch valves.  

"Good Controllability" is a relative term.  If the valve gives you the results you need, then the controllability is good.  You will have, I assume, a low-pressure application with limited velocity.  That makes it easier to apply a pinch valve.  If the fluid is whistling along at 15 M/sec at 50 bars, your valve choice would be different.

Good control is provided by the valve control surfaces going where they are supposed to be in response to a control signal.  Pinch valves have huge unbalanced areas, and the flexible tube can flutter just like the neck of a whoopie cushion.  But if you apply the valve at 2-3 meters/sec, it is both much less likely to flutter and much less likely to be consumed by erosion than if the velocity is higher.   Spend some extra bucks and go a size larger on the actuator, and use a precision positioner.

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