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Venturi Vacuum

Venturi Vacuum

Venturi Vacuum

(OP)
I have an application where I want to confirm air-flow in an extraction duct. At present we use a diaphragm type vacuum switch which measures the vacuum from a smaller L-shaped pipe fixed in the middle of the air flow, i.e the venturi principle.

The vacuum switch is unreliable. I have measured the vacuum at 55mm water. This with a simple water tube.  This equates to 5.5 milibar (if my calculations are correct).
The range on the vac switch is 5~50 milibar.

My question is how can I increase the vacuum to bring it closer to the switch mid-range?

Would a funnel type opening on the end of the venturi pipe help?

Regards,
Speedy

roll1roll1roll1

RE: Venturi Vacuum

Speedy, what you describe is a Pitot tube, not a venturi. Are you sensing differential pressure between the tip of the Pitot tube and the wall of the duct. If not, static pressure changes in the duct will affect your reading.

RE: Venturi Vacuum

More correctly, it sounds like a total pressure probe.

If you simply need to know flow or no flow, a sail switch might be a better choice.

RE: Venturi Vacuum

(OP)
Thanks for your replies.

To clarify - it is in fact a pitot tube, with no static pressure measurement. It's function is to clarify FLOW / No FLOW.

I like the idea of a sail switch, but I have to find one with ATEX approval.  

Any suggestions,
Speedy

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