Reverse Suction

by Justin
(CA)

We operate a dental clinic in a remote part of Mexico. While we were in the middle of a procedure, I went to use suction to remove blood from a patient's mouth, but instead of suction, it was blowing air.

We finished without it, but it still does not work right.

Here is the set-up: We hook up an air compressor outside to a line that goes through the wall into the building, where it then seperates into two lines, one to each dental chair. Once it reaches the chair, I can plainly see that it connects to a regulator, similar to this one http://www.norgren.com/document_resources/USA/R06.pdf
From the regulator it splits into two lines, one running towards the suction tank, and the other towards the water.

The regulator has no other openings/holes, but it does have and adjustment knob on it, but we both increased and decreased it and nothing change, except the suction tube was blowing less.

We weren't sure if its the regulator that causes suction or some other piece of equipment. We don't see a vacuum pump/unit anywhere, so we guessed that this was the problem.

Also, the other chair was operating fine, and on this chair we still had water pressure, just no suction. If you can think of what would cause this or how to fix it, it would be greatly appreciated. Thanks.

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Bill says...

Hi Justin.

In order to have suction, you must have a vacuum device of some kind.

Often, it's a venturi vacuum, one that pulls air through one orifice as compressed air passes over a venturi inside the vacuum generating device.

Since you don't, apparently, have a vacuum pump, then perhaps, in your air circuit, you have these small, very effective, and substantial compressed-air-consuming devices.

So how come a line that's supposed to pull a vacuum suddenly blow air?

I'm thinking that, if the compressed air path through the venturi device, if that's what you have, were blocked, compressed air would blow out the suction tube, instead of passing through the device and carrying the vacuumed debris downstream with it. Check the lines running to what you call the vacuum tank, and what I think of as a waste receptacle.

In your setup, I think the regulator's purpose is to increase and decrease the pressure of the air through the venturi, thereby increasing or decreasing the amount of vacuum that it's pulling.

I don't think you have a regulator problem, I think that if your vacuum source is a venturi type device, that you have a blockage downstream of that device that's backing up the air, and forcing it out the vacuum tube.

Hard to be sure without seeing it. I hope this helps.

Cheer,

Bill