Pump capacity necessary to water 20 acres of turf in Fort Collins area.
I live in an HOA just east of I-25 in Windsor that uses a pump and pond to water about 20 acres of turf with raw water. Our existing pump has a capacity of 500 gpm @ 90 psi. We are planning on refurbishing our system, and are wondering if our existing pump is oversized. We have not been able to find any of the original design specs, drawings, or plans.
Do you have any sort of "rule of thumb" on needed pump capacity per acre?
Larimer County Colorado
There is no rule of thumb on pump capacity per acre. Pump capacity is dependent on so many variables that there are no simple rules for determining size. Pump size/capacity depends on a number of variables, including:
1. pumping from a pond vs. well
2. elevation changes from where the water is being pumped to to highest spots in the system (pressure loss due to elevation)
3. mainline pipe size and run (pressure loss due to friction)
4. lateral pipe sizing and run (more friction loss)
5. number of heads per station and their optimal operating pressures - as well as existing spacing.
6. types of valves and backflow preventer (and even existence of a water meter after the pump) are also sources of pressure loss.
Total pressure loss for the system (i.e., which part of the system/station has the HIGHEST pressure loss) must be calculated in order to size the pump properly - or parts of the system won't operate properly if the DESIGN PRESSURE LOSS is lower than the TOTAL PRESSURE LOSS.
It's also important to know that two pumps can have the same exact horsepower and produce radically different flows and pressures - so just replacing a pump with one of apparent equal horsepower doesn't always work.
Without the original specs that show existing pipe sizing and run lengths (for mainline and laterals) and valve specs (for pressure loss), it is much more difficult to do these calculations. You can get the specs for the sprinkler heads and count how many per station, but you still need the pipe (size and run distance) information to calculate pressure loss between the pump and the highest (elevation change)/farthest /largest (# heads) station in your system.
You want to be sure that the pump you select is sufficient, but not oversized (which is a waste of money).
At this point, my recommendation would be to hire an irrigation specialist or company that specializes in irrigation system design and pumping systems. A couple of places to start:
CPS (CO Pumping Supply) Distributors
207 N. Timberline Rd.
Fort Collins, CO 80524
Thanks, and good luck!