Help, our venturi doesn't work

Rushmore X · #1 (**permalink**) 01-11-2009, 05:54 PM

Help, our venturi doesn't work... The pipe coming up off the 1/2 hp pump is 3/4 inch. It makes a 90 degree bend going into the venturi. The venturi has a reducer that goes down to about 3/8 inch. (3/4 to 1/2 adapter with copper solder in to further reduce. The end of the nozzle extends just about to the end of the air inlet on the tee (1/2 inch air inlet), so the oil shouldn't be able to turn back and go out the air inlet, but it does. The 3/4 inch pipe coming out of the tee is about 7 inches long. We then have a 45 degree bend, going into another 8 inch straight piece, then a 90 degree elbow going into the tank. When we tested the setup with water, it did have a slight vacuum, but with oil, oil actually drips out the air intake in a steady stream. What is wrong with our engineering? My thought is that there is to much back-pressure from somewhere, causing the venturi to blow rather than suck. If anyone needs a pic, I can send it since I can't attach it to this post

thanks,
Trent

fabmandelux · #2 (**permalink**) 01-11-2009, 07:00 PM

To much restriction on the output side. Especially the 90 deg elbow. In a fluid circuit a 90 deg bend is equal to adding a 20' length of straight pipe. Try it with just a short straight pipe into a bucket, and you should see vacuum.

Rushmore X · #3 (**permalink**) 01-11-2009, 07:10 PM

Quote:

Originally Posted by fabmandelux

To much restriction on the output side. Especially the 90 deg elbow. In a fluid circuit a 90 deg bend is equal to adding a 20' length of straight pipe. Try it with just a short straight pipe into a bucket, and you should see vacuum.

thanks, that's what I was thinking. Woud replacing the 90 with 2 45's with a straight piece in between (for a total of three 45's) be better, or would there still be too much restriction?

fabmandelux · #4 (**permalink**) 01-11-2009, 07:22 PM

Probably still to much restriction.........Are you pumping the mix vertically? That would also add to the back pressure. If your pumping horizontally you could increase the pipe size, and possibly reduce the restriction.

Rushmore X · #5 (**permalink**) 01-11-2009, 10:31 PM

Quote:

Originally Posted by fabmandelux

Probably still to much restriction.........Are you pumping the mix vertically? That would also add to the back pressure. If your pumping horizontally you could increase the pipe size, and possibly reduce the restriction.

no, have it mounted horizontally. Think just might have to re-plumb it with the venturi going into the tank, and the elbow going into the venturi from the pump. Will still try and use 45's instead of the elbow though.

Rushmore X · #6 (**permalink**) 01-12-2009, 09:03 PM

Spent most of the day re-plumbing the venturi. I made the copper one go straight into the water heater. Didn’t make a difference as far as vacuum, but at least it didn’t blow. Anyway then made the version with the ¾ inch black iron pipe as an educator. nozzle is 1/2 to 3/8 compression fitting. Still no vacuum. All the elbows are before the venturi now. there is a 10" straight pipe going from the venturi into the water heater.

fabmandelux · #7 (**permalink**) 01-13-2009, 05:26 AM

Quote:

Originally Posted by Trent Fliginger

Spent most of the day re-plumbing the venturi. I made the copper one go straight into the water heater. Didn’t make a difference as far as vacuum, but at least it didn’t blow. Anyway then made the version with the ¾ inch black iron pipe as an educator. nozzle is 1/2 to 3/8 compression fitting. Still no vacuum. All the elbows are before the venturi now. there is a 10" straight pipe going from the venturi into the water heater.

Send me a picture.............If you click on my username it will lead you to my reg email address. I need to see what you have built. I'll be gone most of today on a job, but look at it when I get back.

Rushmore X · #8 (**permalink**) 01-13-2009, 05:43 PM

will do thanks!

fabmandelux · #9 (**permalink**) 01-14-2009, 09:58 AM

Ok Trent, got the pics! It looks like you don't have the "nozzle" in the venturi in far enough. It must be in farther than the "opening" in your "tee" in order for it not to feed pressure into the tee. What is your reasoning in using the venturi? If it is to mix in the Methoxide why not introduce it ( the methoxide) in the Pump intake?
If you put your venturi in the pump suction side you'll have plenty of vacuum to Pull the methoxide in.

This is another reason I prefer an "open" style processor with mechanical mixing.................

Rushmore X · #10 (**permalink**) 01-14-2009, 01:19 PM

Thanks for looking into it. Will try and rebuild it again having the nozzle back further as you suggested. Also, the oil temp was about 40 degrees. Does it need to be heated to about 120 for the venturi to work better. The design we are trying to use is a GL Eco-processor. The venturi is supposed to introduce methanol vapor back into the reaction to help dry the oil. The methoxide itself will be induced before the pump.
Do think that there are too many elbows? We did that so that the pump would be closer to the reactor and the wash / settling tanks could be close by, but if I re-plumbed again, I might be able to get rid of as many as 3. Also thinking of replacing as much 3/4" pipe on the output side as I can with 1" to reduce restriction.

thanks again.