Replacing old single speed with Intelliflo

[cobra46]

A few months ago we moved into a house with a smallish pool that was built in 1993. Over the winter we didn't need to run the pump much so the inefficiency wasn't a huge deal. Now that things are warming up it's time to replace.

I found a nine month old Intelliflo on Craigslist for a good price. I had this pump on my old pool so I know how efficient it will be. I've never replaced a pool pump but have done a fair amount of PVC work on irrigation piping.

I'm soliciting tips on the best way to install the pump. The manual says that I need 5x the pipe OD of straight run on the intake side. This is just shy of 12" on my 2" pipe (OD of 2.38"). My current pump has maybe 2x the OD before the elbow. What's the best way to solve this issue?

Thanks in advance.

 

[JasonLion]

I wouldn't worry about that straight pipe requirement. Most people ignore that and it is quite rare that it causes a problem.

 

[cobra46]

I wouldn't worry about that straight pipe requirement. Most people ignore that and it is quite rare that it causes a problem.

Thanks for the quick response. I'm guessing this requirement is an efficiency issue. I'm a mechanical engineer by trade so I'm by no means a hydrology expert, however, I have a better than average understanding of fluid flow.

The mechanical design software I use all day can model fluid flow. Maybe I'll model it up with different intake lengths and see what it looks like. My guess is that the length requirement reduces swirling caused by the elbow and swirling flow entering the impeller is less efficient.

 

[JasonLion]

I believe it has to do with priming, and does not affect efficiency once the system is primed. Failure to prime is the usual symptom that there is a problem.

 

[cobra46]

I got curious so I modeled it up. What this means to the pump I'm not sure.

The bottom of the pipe in my models is what comes up from the pool. The open ends are what would go into the pump. The flow is very parallel and gets disturbed by the elbow by varying degrees dependent upon length after elbow. The files are named after the ratio of the length after the elbow. For example, 2 to 1 means the length of pipe after the elbow is two times the diameter. I included one solid image since wire frame solid models are sometimes difficult to visualize.....even for those if us who look at them all day.

Not sure if this is useful for anyone but it's still kind of cool to look at.

 

[JasonLion]

Cool pictures.

My understanding is that water flow in a typical pool plumbing environment is almost always turbulent.

 

[cobra46]

The simulations were ran with 2" schedule 40 at 25 gal/min.

 

[mas985]

The part you didn't model is what happens in the pump basket. That creates it's own turbulence so I don't think the length of the pipe that precedes it makes any difference what so ever to the flow into the pump inlet. That would be interesting to see if you can model that too.

Also, I believe the 5x requirement was a hold over from the water distribution industry where the pipe is directly connected to the impeller inlet and there it does make a difference but those pumps are more prone to cavitation than a residential pool pump.

 

[Poollife]

I am in the hydraulic field and although it is water and not oils the principles are the same, the length of straight pipe run is not an issue as long as you have some straight pipe before the pump, the straight pipe is there to recover from turbidity, the pump though doesn't need the psi to be able to recover so as long as your pool doesn't have a lot lf 90's and pulling from the bottom of the pool only the pump will have no problem with that run either entering or exiting the pump.

 

[mas985]

Turbidity is not the same thing as turbulence. Did you mean turbidity or turbulence?

Turbidity is a measure of water clarity how much the material suspended in water decreases the passage of light through the water. Suspended materials include soil particles (clay, silt, and sand), algae, plankton, microbes, and other substances.

In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and flow velocity in space and time.

This by the way happens in straight pipe as well. It is just different type of turbulence (symmetrical vs asymmetrical).

Also, it doesn't matter if you pull from the bottom of the pool or the top of the pool, the static head to the pumps is the exactly same because that is determined by the surface level of the water not where you draw from.

But I still maintain that when you put a pump basket between the pump impeller inlet and the straight pipe or a pipe with a 90, there is no difference in the turbulence entering the pump impeller inlet.

 

[robl45]

For the intake side, you could elbow out and around to get more straight pipe for the intake, but that will likely be much worse than leaving it as is.

 

[cobra46]

The part you didn't model is what happens in the pump basket. That creates it's own turbulence so I don't think the length of the pipe that precedes it makes any difference what so ever to the flow into the pump inlet. That would be interesting to see if you can model that too.

Also, I believe the 5x requirement was a hold over from the water distribution industry where the pipe is directly connected to the impeller inlet and there it does make a difference but those pumps are more prone to cavitation than a residential pool pump.

Mas,

I believe you nailed it. Any sort of swirling that goes on in the intake pipe probably doesn't make a bit difference once the water hits the basket cavity. Maybe if I get bored I will model this too...just for curiosity.

 

[mas985]

It isn't just the sudden expansion but also the basket strainer as well. That must affect the flow to the impeller in some way. It may even out the flow some because the basket holes are so small they create small vortices that would dissipate quickly. That's why I think there is way too much going on in the basket area that would override any effects that happens before that.