I'm not sure if anyone has posted this information or not, but I thought I would post a little something on the subject of: Pump considerations when designing a Aero/Hydro system. Given that there are volumes of engineering books on fluid dynamics and pumps; I just wanted to disseminate the most basic pertinant information which I acquired while trying to figure out which pump would meet my needs.

I am increasingly seeing people making recomendations on pumps based on Gallons-Per-Hour (GPH). This bothers me because GPH is only half the equation. Depending on the application, the head specification of a pump can be more important than the volume of flow. This is especially true when misters/sprayers/foggers/etc are involved.

For example lets look at the average mister from the drip irrigation isle of your local home building supply store. Most of the misters I've seen near me are rated for 10 Gph at 30 PSI. Now, in theory, if there is 0 difference in pump/mister height and there is no dynamic pressure restrictions from bends in the tubing etc, then the conversion factor to turn the head rating (Feet) of a pump to pressure (PSI) is .434, for example....

Pump A is rated at 330 GPH and 150" inches head. Using the conversion factor mentioned above the pressure this pump is capable of would be....

150 (in.) / 12 (in. per foot) = 12.5 Feet of head
12.5 feet x .434 = 5.425 PSI


Now, take a look at Pump B. It is rated at 330 GPH and 115 Feet head. This translates to...

115 x .434 = 49.91 PSI


So both pumps are rated roughly the same in GPH, but the pressure they are capable of producing is very different. So remember to consider the target PSI of your system when choosing a pump.

BTW, in theory you want to match the PSI requirements of your pump to your misters/sprayers, but in practice you can drive the 30 PSI misters mentioned above with a pump that has much less pressure and still get satisfactory results.

Very informative, I know I struggled with pump dynamics while building my first few systems. I'm suprised there's not more threads on here devoted to the subject. Also, if you look at the specs on those two pumps there's a sizeable hp difference (between 0.06 and 0.5).