Does venturi orientation matter?

[Slickdonkey]

I'm in the process of rigging up a DIY ozone "reactor", which is basically just some tubing with the ozone injected into a venturi valve with water passing through it. See http://reefkeeping.com/issues/2006-04/rhf/index.php#21.

Anyway, does the orientation of a venturi matter? When I started pumping water through it, it sprayed out the venturi. Did I pump water through the wrong direction or is my valve defective? I'd just turn it around but it will take half an hour to do... no sense doing it if it's a waste of time.

This is the valve: http://www.marinedepot.com/md_searchstatistics.asp?SearchStr=venturi&action=view&idProduct=KM2851. I suspect I got it backwards because it says "3/4 FPT inlet". Of course this is the one I hooked up as the outlet!

 

[Slickdonkey]

Well I reversed it and it worked for a few seconds before spewing water out the venturi (which is a few seconds more than I got oriented the other direction).

I think I have too much back pressure on the venturi, but I still didn't think they were supposed to spray water even under these circumstances. Isn't the little inlet like a check valve so water doesn't flow out of it?

 

[Meche]

Isn't the little inlet like a check valve so water doesn't flow out of it?

No.

What is the flow through the venturi?

 

[Meche]

As the cross-sectional area of a pipe (the venturi) decreases, the fluid's velocity will increase. This is because the flow rate (gal/hour) must remain constant.

As the velocity increases the pressure will decrease. I'm not going to work out the math right now, but it is conceivable that if the pressure was too high to begin with, it will not drop below atmosphere (14.7psi) to be able to suck air in. If the pressure doesn't drop below atmosphere, then it is above atmosphere, and will spit water.

 

[Slickdonkey]

Well the idea is to use an air pump to inject the ozone into the venturi. I tried hooking it up but it blew the cap right off my air dryer, so there must be a lot of back pressure.

 

[Meche]

How far below the surface is this?

 

[Slickdonkey]

Eh? No water surface, it just drips into the sump. Check out the link I posted.

 

[Meche]

Doing that now. What is your flow rate?

the water's flow rate is about 90 gallons per hour

 

[Meche]

The only situation where aquarists might not use an air pump would be if the air/ozone mixture were being sucked through the ozone generator into a venturi, a common device on many skimmers, that allowed it to then enter a reaction chamber of some sort.

I've herd of venturis not working right when they are force fed, but I personally haven't done it. Is the air pump necessary for your design? Do you have any diagrams or a DIY webpage you used to do this? I'm having trouble imagining what you have built.

 

[Slickdonkey]

Basically I just have 100' of tubing in a coil that drips into the sump. Doesn't matter what the flow rate is, even if I barely crank the valve open I get back-pressure on the venturi.

Tonight I will try hooking the air pump into the venturi and increase the flow rate. I was afraid of water shooting into my air pump so I'll try a check valve or something.

 

[Slickdonkey]

Well that did it -- air pump with check valve keeps the water from shooting out.

 

[Meche]

So you took your air dryer out of the process?

 

[RandyStacyE]

Well the venturi itself is not symmetrical on both ends from the center. I would say that it does matter which end you put water through it in order to properly induct air/gas. I wish I could say precicely which end the water should be fed ... I don't know by looking at the pic. Didn't it come with any diagram or instructions on or in the box? Does it say "IN" or "OUT" on the venturi itself? That's strange ... maybe you could call Marine Depot ... they should be able to tell you for sure.

 

[Slickdonkey]

So you took your air dryer out of the process?

Yes, I had to ditch the air dryer. There's just too much back pressure. I got tired of baking those beads anyway.

Didn't it come with any diagram or instructions on or in the box? Does it say "IN" or "OUT" on the venturi itself?

Actually there were no instructions that came with it, but if you look at the item description it says: 3/4" FPT inlet, 3/4" MPT outlet. So that's the missing information.

 

[DonW]

What pump (water) and tubing size are using?

Don

 

[Slickdonkey]

What pump (water) and tubing size are using?

I teed off my return pump (Sequence Hammerhead) with 3/4" tubing, same as the venturi.

 

[DonW]

I teed off my return pump (Sequence Hammerhead) with 3/4" tubing, same as the venturi.

You dont have a valve on the end of the reaction tube do you?

Don

 

[Slickdonkey]

No, there is a gate valve right at the tee to control the flow through the tubing. No valves of any kind on the ozone tubing (except check valve).

 

[RandyStacyE]

DUH! I can't believe I didn't see that.

 

[DonW]

No, there is a gate valve right at the tee to control the flow through the tubing. No valves of any kind on the ozone tubing (except check valve).

Just wondering. You said dripping into the sump. Is it slowed to a drip or are you pushing a good amount of water?

Don