Venturi

Have a look at this and then please post further comments:

http://en.wikipedia.org/wiki/Injector

Solve for the throat pressure using Bernolli equation. The velocity head will increase while the pressure head drops according to the ratio of diameters.

So far as you already pointed out, we don't have enough information on the input. I suspect that the throat diameter is too large, but more information on flow is needed.

You are right. The suction injection point to be in the funnel portion where pressure dips. Cross section area difference creates pressure difference and more than 45 degree funnel angle and area reduction to 40% at funnel neck level likely to gives better suction.

John correctly pointed out that in the initial pressure build up some condensation will take place and hole being in high pressure zone some liquid may flow out along with gas.

In one design I had, I have injected in the mid of the funnel portion after drilling a hole and inserting tube with opening towards flow direction. I used this to shuck out acid fumes. I also attached another funnel to the suction tube inlet and that did the job of fume collection.

A possibility is that you are using 'wet' normal compressed air and so the reduction in the air pressure inside the venturi will form condensate and liquid inside the venturi?

John.

I'm with Charlie R on this (not literally you understand )

The 8mm hole is too big.... Start small and then inrease it, say 2mm? and maybe have it as a short length of pipe projecting into the middle of the flow.

Be sure to let us know the results of your experiments.
Have fun

Del

What is your pressure in front of the tube?

A Venturi can reduce the pressure but if the internal pressure is still too big the inside will use the hole to go outside! It is very possible that your static remnant pressure is still too important with respect to the outside pressure. As an other comment said try to solve the equation of total pressure and see how much you have to reduce it. If not you will make a lot of tests without good results do not believe that always a test is better than experts comments as one of the participants believe.

I have read your problem andvarious other comments associated.But I think you need to concentrate on what amount of suction you need to create in this 1" line and what are the other parameters lile inlet pressure,type of fluid etc to design accordingly.

M S Vilkhoo

AGM(Inst)

Siel Chemical Complex:Rajpura(INDIA)

I had to suction the condenste out of a Methanol tank out in a tank farm oce. I built a venturi from scratch with a 1/4" Brass Tee (Parker Hannifin), I stuck the metallic part from a wire connector (stub) and connected everything to a plastic tubing with Brass 1/4 nut with ferrule and all. It worked fine, after a little adjustment of the stub. The optimum vacuum was obtained by pushing (calibrating) the stub evermore slightly towards the exit end just over the "T" or suction part.

As others have said what is the input pressure and velocity.

Also: what (gas or liquid) are you pumping through the tube.

Venturi sizing is an art all of its own. I agree with the other posters that your orifice sizes are way too big. You would need a cudzillion GPM to generate any suction.

I always consult with the sharpest gurus of the industry, regardless of the application. My liquid venturi guru is Gerald Lott of Vortex Ventures. Tell him Delmar sent you.

Click http://www.vortexventures.com/

Can an injector/ejector design do the job? If you want to design an apparatus for creating a vacuum you should do it around the equations and fundamentals of nozzle injector/ejector design. They do a great job of suctioning liquids!

There is no design approach. OP built something, reported that it did not work, and left us all guessing as to what his criteria was. Most have suggested he tell us something more. Hasn't happened yet.

I went ahead and edited my comment? I felt is was too rash! Thanks for pointing it out...

Ron

injector/ejector or eductor.

I have designed (if you call trial and error designing) an eductor for injecting salt into a brining operations.

Things like this, is complicated if your looking for formulas, if you have some experience trial and error tends to work best at least to build a point of reference to build off.

nick name ask the right question. what are you using for motive pressure & how much?

Since you've not given your design let me put it this way.

Suppose your venturi is an inverted tee. the bottom in suction, on end discharge and the other end motive air/steam jet . as the air jet proceeds you get the suction out.

This is know as ejector. You you utilize eg. steam vapor exhaust at 0 psi say 2000 kg(like in Bleaching Steaming Chamber) to be utilzed at 30 psi. You design your venturi throat and inject steam at designed pressure say 100 psi. There is a jet at the centre point of the suction and this then pulls up the 0 psi exhaust mixes with the 100 psi pressure in the throat dropping down to 30 psi to give this 2000 kg to something.

this is known as thermocompression. Invert it = ejector.