# Help with water pump calculations

1. Apr 4, 2015

### DannySmythe

I have a rain barrel 20 feet below a deck. I want to pump water from the rain barrel up to a small container (2 gallons) once a day. I'm thinking it should take less than 15 minutes to fill.

4. Apr 5, 2015

### DannySmythe

I found a pump (Rule IL200) that had a chart of lift vs flow so I got it.
Just for fun here are the numbers:
Max Flow 3.3 GPM
Max lift 25'
Flow at 15' (my application) = 1.3 GPM
So it will take a couple of minutes to fill my 2 gallon container.
Thanks to all for info.

5. Apr 6, 2015

### Staff: Mentor

I take it you found the performance curve? Yes, pump manufacturers will often quote max flow and max head, but that doesn't tell you what the flow is for your application: you need to find your operating point on the curve. Glad you figrued it out.

6. Apr 6, 2015

### DannySmythe

The chart only had a few entries. Lucky for me one was 15' head.
But in thinking about it, assuming the hose is the same diameter as the pump port, isn't the flow just proportional to (Max head - App head)? Where App head is the head needed for the application.
For example at an 'App head' of 0' the flow will be the rated flow F and at an 'App head' of 'Max head' the flow will be 0. So can't I just draw a straight line between these 2 points and pick my operating point? Or is it really that non-linear?

7. Apr 7, 2015

### Travis_King

1) It's non-linear, very much so.
2) Be aware that 15' is the total dynamic head. This is the static head (difference between the elevation of the pipe discharge and the surface elevation of the supply water) plus the dynamic head ("pressure" loss due to the friction between the fluid and the pipe as it flows through plus all losses due to direction changes and fittings). At 1-2 gpm in a 0.5" pipe that shouldn't be all that much, but depending on the length of pipe, could start to add up. For 25 ft. of hose I'd estimate an additional 1 ft. of dynamic head at 1.3 gpm. Since fluid systems tend to balance out, I'd take a thumbsuck guess and say you'll likely see something like 1.2 gpm. Not that that makes a huge difference for your application, but you should be aware of how pumps are actually sized for next time.

8. Apr 7, 2015

### DannySmythe

Good to know.
Thank you.