DIY Aspirating Venturi Design?

[Brian Prestwood]

This question is about the venturi itself, not the whole skimmer. Has anyone compared the performance of different DIY aspirating venturis (AVs)?

I make an AV that approximates the geometry of the injection molded AVs I've seen on most AV skimmers. I use gray conduit PVC fittings. I fit the following pieces together in the following order...

3/4 FT-FS Coupler
3/4 MS-1/2 FS Reducer
1/2" Tube (1" segment)
3/4 MS-1/2 FS Reducer (turned 180 so 1/2" end faces 1/2" tube)
3/4 FT-FS Coupler (turned 180 so FS end faces MS end of reducer)

After the glue dries I drill a 1/4 hole in the middle for the air intake and insert a 1/4 barb.

I use gray conduit fittings because they are shorter and approximates the geometry of commercial AVs better than schedule 80 fittings.

This works well but I didn't compare it to anything else.

 

[Randall_James]

could you detail this construction with some images? I have fooled around with a few different methods for aeration of effluent for skimming

 

[Brian Prestwood]

Did you make an aspirating venturi skimmer? If so, how did you make the venturi itself?

My digital camera is broken. If you fit the pieces together as I mentioned you get an inner profile that matches the injected molded ones

Unlike exhaust (standard) venturis, intake (aspirating) venturis have a much sharper slope (obtuse cone) and much larger (proportionally) opening.

 

[TekCat]

Yes!!! we need pix!!!!! BTW, what is the "aspirating" thing?

 

[BeanAnimal]

brian the internal shape of the Venturi is a complex animal. The major variables are the input pressure and flow. Form there a throat diameter and length can be calculated. The input and output sections are then tailored to create laminar (non separated flow) through the body.

The sharp edges of the pipe fittings create a LOT of turbulence and reduce the efficiency of the Venturi.

For our purposes (pulling air into water) The input angle needs to be somewhat steep (say 50 degrees) and the output side needs to be rather shallow (say 15 degrees).

Here are decent photos showing the flow modeling of such a design.

http://www.processinnovation.com/Venturi.htm

This topic comes up a lot and people are able to get decent results with DIY designs. However a truly engineered design will yield a much better result. Even mimicking a decent shape with smooth transition will gain leaps and bounds in efficiency.

The other thing to note is that many of the "DIY success stories" are simply poor designs shoved onto the input side of a pump that has a fairly high suction head. By throttling the amount of water than can enter the Venturi, the pump sucks air through the connected hose. The better the shape, the better this works as well. However it is not really a true Venturi.

For the MATH behind all of this... you will need to delve into the Bernoulli principle.

 

[TekCat]

Bean, the link doesn't work.

 

[BeanAnimal]

The page is there... but it has some kind of silly script that prevents a direct link

try
http://www.processinnovation.com/site_map.htm
and then click the venturi link from there.

 

[Randall_James]

Naw, just had a capitol V in venturi
http://www.processinnovation.com/venturi.htm

 

[TekCat]

thanks, that worked! so why is it called aspirating? is there another kind?

 

[BeanAnimal]

must be an apache web server... they are case sensative

 

[BeanAnimal]

BTW the link was copied and pasted from their site... with a capitol V

Kinda goofy.

 

[Randall_James]

I think you meant Linux server and yes they are all case sensitive

 

[BeanAnimal]

Nah.. I meant Apache

Apache is CaSe SenSiTive and IIS is NOT.

You can make Apache parse URLS without regard to cAsE but you can not make IIS pay attention to cAsE.

I don't know too many Windows boxes the run Apache... though I suppose their are some freaks out there who do.

I own an IT consulting company and am also formally trained as a programmer. Kinda funny... I can't stand Linux or Unix... but sure did like VMS. I like the damn MAC better than Linux... I do like penguins though.

Bean

 

[Brian Prestwood]

TekCat

A standard (exhaust) venturi is attached to the exhaust of the pump. An aspirating venturi is attached to the intake of the pump. In either case, the water flowing through the venturi draws air into the main flow.

In the case of an aspirating venturi the air is drawn into the pump intake and further atomized. Some aspirating venturi pumps take it a step further by optimizing the geometry of the impeller to atomize the air more than a standard impeller would.

For short skimmers, a simple PVC T will do for the aspirating venturi because the vacuum on the intake draws the air in. I have a tall skimmer so I need additional draw from the venturi.

 

[Brian Prestwood]

BeanAnimal

Thanks for the article. As you probably know, the geometry the skimmer manufacturers use for aspirating venturis is different than standard venturis. I'm guessing that is to optimize both the intake vacuum and venturi affect.

It looks like Kent is using both an aspirating venturi on the pump intake and an exhaust venturi on the pump exhaust.

Kent makes a nice standard venturi that isn't very expensive. Perhaps they will make an aspirating venturi too.

 

[BeanAnimal]

I think it has more to do with what is cheap to make and the fact they none of them have likely engineered anything. They more than likely have copied another design they saw.. and maybe tweaked it a bit through trial and error. I have not been impressed by any of the venturis I have seen OEM on skimmers.

Space saving is also a consideration I would guess. In the end the bare minimum that works is what wins the day when it comes to the product development cycle.

Bean