Pond Boss Forums INTRO Questions & Observations using a variable speed pool pump for waterfall?

I'm working on a stream that is about 200 feet long that leads into a pond with a 5 to 10 foot drop depending on the season. From computations elsewhere, I believe a pump capable of producing 7600 gph with a 50 ft head is required. There are a few "waterfall" pumps capable of doing this, but their monthly costs are close to $150 per month. I was looking at other options and found mention of variable speed pool pumps that can be programed to lower speeds in order to reduce electrical costs. Since a waterfall pump doesn't necessarily need to be running full speed 24/7, this looks like it could be a decent way of producing a nice waterfall while also lowering operating costs. Presumably the speed would be reduced for "off hours" and then bumped up to full speed when one wants to see or hear the waterfall in operation.

Has anyone used a pool pump for their waterfalls? Any thoughts on this idea? All of the pool pumps I've found that can provide at least 7600 gph are 220v and are inline style, so no electricity in the water as a submersible waterfall pump would be. Hayward makes one that can self-prime up to 10 feet of head, which is about what this pond/stream/waterfall has. Costs are in the $1,000 to $1,500 range which are similar to waterfall pump prices of similar gph rates. Any opinions on this option?

Thanks, Dennis

Dennis:

I have no experience with those type of pumps. I know a pond owner that uses a sump pump type of pump (110v) that is on a timer. It pumps enough water from the pond to make a waterfall that is 48" wide, creates a 48" wide stream that then runs 30' to 40' back into the pond. He runs it on a timer, on at 6:00 a.m. off at 10:00 p.m. It has a 1 1/4" discharge that goes to a one way valve, then immediately up to a 3" pipe that feeds the waterfall. That head is about 6'.

Why 50' head if you only need to lift the water 10'?

The 10 feet is just from the pond water level to the bank of the pond/top of the waterfall. From there going back up the stream to its origin, is another 15 feet. Then there is 250 feet of pipe. Taking everything into count, I was told I needed 50 feet of head rating for the pump. I think it was the calculator on The Pond Guy website. If someone else has a better computation, I'd love to hear it.

Total Dynamic Head is the distance between the water level you are pumping from to the the highest point at which you are pumping to. The amount of horizontal pipe has very little effect, but it can have a bigger effect if you try and push too much water through too small of pipe. In my opinion a pump that can pump 7600gph at a 50ft head is one hell of a pump and yes it will be hard on the electric bill. Not sure on the variable speed pumps though, never used one. Sorry. Have you thought about submersibles? a good sump pump can pump 10ft of head easily if that's all you need. They are cheap and quiet seeing that they are under water compared to a noisy pool pump sitting next to the pond. I'm using a 25 gpm submersible well pump to pump water 70 ft up a hill to the pond and it would probably make an ok waterfall. Norton pumps make these at a reasonable price. Cheapest I have found for the kind of output you get. I think they have a 37 gpm model.
http://www.nortonpumps.com/

Thanks for the link. Unfortunately that pump maxes out at 48 gpm at 50 ft. of head. That is about 1/3rd the water flow I need to work with on a 5 ft. wide waterfall. Regarding the pool pumps being noisy, the new variable speed pumps are much quieter than the old one or two speed pumps. Another reason I'm considering them. They also usually run 24/7, so longevity should be a positive attribute. But I hate experimenting. I plan on using 3 inch PVC, to cut down on friction loss, but there is still 250 feet of pipe to move 125 gpm up 25 feet of actual height. Dynamic head includes computation for friction of the water through the piping. The only thing with either of the pumps below, they have 2 inch inlet/outlet ports. So there will be a pinch for the pump. But since they can produce quite large gpm and head, it shouldn't be a problem. Hayward has two pump models, the one below has a safety shut off if the inlet suction gets blocked.

Here is what I'm thinking about for Hayward:

This pump will self prime up to 10 feet of head to where the pump is located.

http://www.hayward-pool.com/prd/In-Ground-Pool-Pumps-EcoStar-SVRS_10201_10551_21502_-1_14002__I.htm

Here is another company's variable speed/flow pump from Lifegardaquatics:

This pump won't self prime 10 feet of head, but if a check valve holds the water, it will self prime and function correctly. The variable flow model has more programing features than the variable speed model. Though both are basically variable speed.

http://www.lifegardaquatics.com/products/product.php?id=43

I would suggest you lay out the system and determine the actual pipe and fittings needed to do the job. From the BOM you can calculate the system resistance and select a pump from there.

http://www.hunterindustries.com/resources/pdfs/technical/domestic/lit091w.pdf

If we assume the pump efficiency is constant, it takes twice as much power to move the same amount of water to 50' head vs 25' head.

IIUC the elevation between the two bodies of water varies from 20 to 25 feet.
Your target is a fixed volume of 7600 gph.

At that flow rate you are really close to needing a thin wall 3" pipe to keep the velocity below 5fps. However, I don't think it would be a great sin of omission on a system like this.
Class 125 would do it with a psi loss of 1.08 per hundred feet at 130gpm. For ballpark numbers we could round on up to 300 feet of pipe to account for some loss through fittings and you have an additional 7.5 feet of head.

If you kick this up to 4" pipe in the same class the loss per hundred is .32 psi. At 300' the additional head is ~2.25'.

At 28' and 7600 gpm a pump with efficiency of 60% needs 1.5hp
32.5' at that flow is ~1.75hp
50' would be ~2.7

In theory, with the variable speed pump you should be able to dial right into the system performance you are looking for and reduce the speed to save power and retain some flow in the stream. I didn't find any power consumption data or efficiency plots on the Hayward website so I'd be a little suspicious. However, that data may just be a phone call away.

I don't have a complete electrical use for all speeds. But the Hayward pump has a maximum amp rating of 10.9 amps. The Lifegardaquatics pump has a 16 amp full load rating. Both being 230 volt pumps. With speed controls, I believe both pumps allow a range of 10% to 90% adjustment over the rpm ranges of their motors. In comparison, the Atlantic Tidal Wave Pump model 12500 has a 9.4 amp 230 volt rating. But it is a one speed only pump that at 50 ft. of head produces less than 5,000 gph. It is at 9,900 gph at 25 ft. of head.

Regarding pipe sizes, 3 inch seems to be the most reasonable pipe size for the gph requirements.

Are there other pumps that I am over looking?

yeah i didnt see you were going with a 5 foot wide waterfall ...48 gpm might not be enough well when you get it done make sure to post some pics..should be something to see...good luck...oh and 10 amps doesnt seem too bad for the output you are going to get...depending what your electric rates are maybe 60- 80 dollars a month? small price to pay for something that should look really good....just cancel the cable to off-set the cost

Overall, assuming the pump curve is accurate, the Hayward pump looks like a pretty good solution. Assuming 10.9 amps the pump has a peak final efficiency of ~60% at 3450 RPM. It looks to me like it has infinite variable speed adjustment between the min and max range.

This is can be really important if the interest is in energy savings and the pump is going to run allot. You can dial right into the operating point you want. The power consumption of a pump changes at the cube of the speed. A 10% change in speed provides an energy reduction of 30%.

As to what pipe size is reasonable only you can answer that. You have to have set down some operating parameters and calculate back from there. There would be very little full output variance from the pump from either 3" vs 4" pipe size. So if it was a single speed pump 3" makes sense. For that matter 2.5" class 160 will exceed your target and flow about 144gpm with that pump.

However, with the variable speed pump in which you can dial right into the operating point the 4" pipe would save about 190 watts at your targeted flow rate over 3". Not a big deal if you only run a short period of time at that rate, but it's almost a 10% reduction and will be significant if you run there for an extended period of time. If you run the pump at full output 160gpm the savings are about 15% or about 375 watts.

At 2075 rpm there wont be a great deal of difference between either pipe size and you'll still have some flow ~40gpm through the system.