pump size for dedicated 40 gpm waterfall

[skirt]

What pump size do I need for a dedicated Ricorock waterfall that will work with a minimum 40 gpm flow (waterfall will sheet @ this flow rate, but will handle up to 80 gpm). The waterfall will be supplied by a dedicated skimmer. The supply and return line are both 2" pvc. I'm looking @ an energy eff pentair whisperflo, but would like input on the horsepower.
Thanks

 

[mas985]

This table from the hydraulics sticky might help:

Whisperflo

All the pumps in the table will probably hit the minimum but if you want to get closer to the maximum, the 1 HP should be enough. To make sure, how long are the runs from the skimmer to pump to waterfall?

 

[skirt]

The run from the skimmer to the pump is about 50' and the run from the pump to the waterfall is 45'.

 

[mas985]

The head loss should be quite low since there really isn't anything other than pipe that would create much restriction. So assuming a total of 380 feet of pipe (I used a 4x factor to account for fittings) and a 6 ft high waterfall (wasn't sure about this), even a 3/4 HP pump will give you close to 75 GPM. A 1 HP, 86 GPM so you can decide how much margin you want but like I said before any pump will probably give you more than 40 GPM so if that is all you really need, then you could go with the smaller pump.

I have a 1 HP Northstar and with a filter heater and a lot of valves, I still get over 88 GPM so I would think a 3/4 HP should be enough to get 80 GPM without the extra equipment.

The height matters somewhat so if the waterfall is higher than 6 ft. let me know. Also, do they tell you what happens if you exceed the maximum flow rate? You can always put a ball valve on the output of the pump to reduce the flow rate if needed.