Wrong Waterfall pump?

[ldcsteelers]

My PB installed the plumbing yesterday and I noticed that the waterfall pump was a Supermax 2HP 2-speed pump. I was supposed to get a "Waterfall" pump from Pentair.

A quick calculation says I have about 15 feet or so of Head loss (waterfall 3' above pump, 60' of 2" pipe, 3" suction, and around a dozen elbows".) By reviewing the performance curve of the Waterfall Specialty pump it looks like it plays well with that amount of head loss but the Supermax pump is outside of its efficiency curve.

Will the Supermax be ok, or should I make the PB replace it with the Waterfall pump?

 

[JasonLion]

Hopefully our plumbing expert will come along soon. He can give a much more reliable answer than I can.

In the meantime, it looks to me like that pump will be at least close to the edge of it's operating range, though outside, not nearly as bad as your estimate. It sounds like roughly 200 feet equivalent pipe length, given all the fittings. At 90 GPM that is a TDH of about 30, and once you add in the 3 foot rise, you are getting fairly close to the TDH of 40 at 90 GPM that is the closest point on the pump curve that is inside the pumps operating range. Overall, yes, it looks like that will be outside the efficient operating range for that pump, just not by as much as you calculated.

 

[ldcsteelers]

I guess I didn't account for that high of a flow rate. Is 90 GPM typical for waterfalls? I honestly don't know, I've never had one before. If it is, I'll feel a lot better about the pump they installed.
Thanks for your calculations, that helps.

 

[JasonLion]

Waterfalls vary a great deal, mostly depending on how wide they are, but also on the kind of effect you are trying to achieve. I picked 90 GPM because that was the closest point on the pump curve, that was within the operating range, to where the plumbing balanced out.

 

[mas985]

You run the risk of the SuperMax going into cavitation when operating to the right of the right most point on a head curve. So I would get the correct pump which is a low head waterfall pump.

But exactly how did you calculate the head loss? If I get time I will run a calc as well.

 

[ldcsteelers]

Well, I went here and used the chart to get my head loss for 2" PVC. The GPM I used was 60 because I frankly don't know the flow rate of the waterfall. It's going to be custom built.

I didn't like the chart from the above link for the fittings. They seemed off because the larger fittings showed a greater head loss so i questioned the accuracy. So... I went here and used their's. With about a dozen fittings (a few are 45 pairs), I rounded up to 100' extra pipe to compensate. That all added up to around 9 TDH. Then I added the height of the waterfall (3 feet), and added a few feet for suction. That added up to roughly 15'.

 

[JamesW]

I suspect that the waterfall pump would be a better choice. Many builders use a medium or high head pump on waterfalls, but it's usually not the best choice. Waterfalls are low head, high flow and a waterfall pump is designed for that application. The medium to high head pump will usually be noisy and it can use much more power than a properly sized waterfall pump.

What specific waterfall did you get (make, model, size)? Even if the waterfall is going to be made custom, it will usually use a manufactured waterfall fitting. The fitting will specify proper flow rates.

If there won't be a manufactured fitting, then if you could describe the dimensions and desired effect, we could help determine an ideal flow rate range.

 

[ldcsteelers]

I believe he's just going to direct the water flow into a small pool at the top of the structure. The waterfall will be 4 feet tall and pour into both the pool and spa. There are 2 pipes plumbed to the waterfall with a valve to switch between them. One flow will go to the pool, the other to the spa. This will allow the spa users to enjoy the waterfall without loosing all their hot water.

 

[JamesW]

The design details should help decide the correct pump. In any case, I think that the existing pump is probably not a good choice.

One possibility is to use a variable speed pump like a Jandy vs flopro or a Pentair SuperFlo vs. That way, you could adjust the flow to suit the application.

Another option would be to not use a fountain pump. You could just use valves to direct some of the return water to the fountain.

 

[mas985]

So based upon my calculations, I get around 19.5' of head loss at 117 GPM which is beyond the up rated 2 HP head curve. So definitely an issue. I think it would beyond the full rated curve too.