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Venturi system failure
http://byap.backyardmagazines.com/forum/viewtopic.php?f=8&t=21973		 Page 1 of 2
Author:  bdornis [ Jun 7th, '14, 09:41 ]
Post subject:  Venturi system failure
I've been following RobBob on youtube for quite a while now and soaking up all his videos. He showed a venturi design that I've basically replicated (and he got it from ccBear)

In one of his videos he had it set up where you can see his venturi enters a blue barrel near the bottom.




I've got my system setup pretty similar with regards to the venturi. The idea is to use the venturi to move the biomedia in the same manner.

The problem I'm having is water is traveling up the venturi tube. Here are some photos of the venturi.

Image

Image

The pump I'm using is a 3000gph (11000 lph) pump with a head-height of 17ft (5m). There is a good amount of flow coming out of the pipe in the bottom of the blue barrel but no air is being sucked in. Instead the water flows up the tube. (I've marked the venturi to ensure that the angle is facing the right direction.)

The pipe goes from 1" (25mm) to 1/2" (13mm) back to 1"

Any help would be greatly appreciated.
Author:  Ronmaggi [ Jun 7th, '14, 09:47 ]
Post subject:  Re: Venturi system failure
Have you tried blowing on the pipe to clear out the water and perhaps kickstart the Venturi effect?
Author:  Stuart Chignell [ Jun 7th, '14, 10:06 ]
Post subject:  Re: Venturi system failure
:whistle:
Author:  bdornis [ Jun 7th, '14, 10:07 ]
Post subject:  Re: Venturi system failure
Yeah, I did that a few times and the water just reverses right back up. :( It's not hard to blow either so I can't imagine the pressure is too great.
Author:  bdornis [ Jun 7th, '14, 10:41 ]
Post subject:  Re: Venturi system failure
Does the venturi tube need to be straight up? Mine has a small kink in it. I can't imagine that having much effect.
Author:  Gunagulla [ Jun 7th, '14, 10:48 ]
Post subject:  Re: Venturi system failure
Proper venturies have a restriction to increase flow rate and reduce pressure, without introducing too much turbulence.
The relevant equation is P1V1 = P2V2 P = pressure, V = velocity

Just sticking a pipe in wont really work very well IMO. If you have a car without fuel injection, take the air filter off and have a look down the carby throat to see what you need to make it work properly.
Author:  Gabe [ Jun 7th, '14, 10:51 ]
Post subject:  Re: Venturi system failure
If i were you i would change the soft tubing venturi tip to something more robust. It may be that the plastic is deforming. You want to maintain a ~ 90 degree angle between the venturi tip and the water flow.
Author:  Bufordht [ Jun 7th, '14, 12:17 ]
Post subject:  Re: Venturi system failure
Is it because the valve after the venturi is closed? Just covering all the bases ;)
Author:  longnt [ Jun 7th, '14, 12:56 ]
Post subject:  Re: Venturi system failure
I think the tube is not insert deep enough into the T to increase the pressure there, as in this case the pressure down stream rather high due to it was located at the bottom of the barrel. You can try to reduce the length of 13mm pipe especially on the down stream side (may cut the T shorter) and better to remove the valve near the barrel.

The better option is to buy a venturi from eBay. It is not expensive but very efficient.
Author:  bdornis [ Jun 7th, '14, 14:11 ]
Post subject:  Re: Venturi system failure
Hah, Bufordht. That is definitely something that's been covered.

longnt, It's adjustable. The reason it appears so short in that photo is that i tapped it on the wood just then trying to get a shot for a photo. I might consider buying one if I can't get this one working soon. The only reason for the valve on the barrel is so that I can ensure I don't have backflow when I need to do some work. :) I could add a checkvalve but i thought that might be a problem.

Gabe, I have some harder line lying about I'll give that a shot in the morning.
Author:  ccBear [ Jun 7th, '14, 14:26 ]
Post subject:  Re: Venturi system failure
These venturi's were never intended to be used through the bottom of the barrel. I tried one up top with the line going to the bottom of the barrel but it did not supply enough air pressure for the bio.

If you look at one of Robs videos after I believe he removed that design and put in one of the commercial ventures he got from Paul. This still had limitations using the 5500 lph eco pump and only really worked when he use a 10000 lph pump which operated on 170 watt.

I have had no problems using the ventures for what I first put them together for. That was introducing a good volume of air into the return line to your fish tank. I have one set up on both my IBC in my RAS and do not use any other air in these tanks. I believe Several other people have had good success in incorporating them into their systems.

I would suggest you PM Rob and ask his opinion on what you may need to do.

Have never worked out how this :whistle: is offering advise but then again I have never put myself up as a expert and can only post on what has worked for me in BACKYARD Aquaponics.
Author:  bdornis [ Jun 7th, '14, 14:33 ]
Post subject:  Re: Venturi system failure
longnt, now that I think about it I should check to see if I might be pushing the tube up into the container tube. Thanks for that hint, something to definitely check on.

ccBear, thanks for the input. Since the video was posted just a few days ago I thought it was still relevant. I might have to ask him for advice specifically about his setup as there might be some minute detail that I've missed or wasn't included.

I'm going to do a few things suggested here tomorrow and see where that gets me. The reason I'm trying this venturi is my neighbor is only 10ft (3.3m) away and I'd prefer to keep it was quiet as I can. Which means I won't be using an air compressor and the quiet air pumps I've tried don't have enough lpm to make any movement (or just can't handle the pressure)

This is all a learning experience for me and reading all the posts here and watching your videos on youtube have been a great help. Thanks to everyone for taking the time to respond.
Author:  bdornis [ Jun 7th, '14, 14:55 ]
Post subject:  Re: Venturi system failure
ccBear, I see what you mean. He replaced that design with a commercial one. Sorry, kinda slow on the uptake there. :) If I can't get this one to work in the next few days I'll probably go down that route.
Author:  Lyndon346 [ Jun 8th, '14, 01:28 ]
Post subject:  Re: Venturi system failure
Have you got the flow going from left to right, if it was inserted the same as your pic?


Image
Author:  joblow [ Jun 8th, '14, 05:31 ]
Post subject:  Re: Venturi system failure
You'll need to mark the way the bevel faces in the fitting so you can see if it's facing the correct direction when it's screwed in place.

Facing the bevel towards the flow will only send water up the tube and have very little venturi happening.
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