I am not an engineer, so be gentle! I need formulas or methods of estimating the horsepower and propeller size necessary to accelerate large volumns of water thru small sections of pipe. Example: If I have a gravity flow sewer pipe 48" ID flowing 6000 gpm, and I want to have all this flow go thru 10" ID pipe for 5 feet,with the effluent being a 48" sewer pipe, how do I figure out the propeller and horsepower needed to pump this flow? The propeller would be inside the 10" pipe. Thanks for taking time to consider my question. Jon Smith

Jon,

You're correct that an engineer should understand how to figure the HP for you. I know the details will need to come out of a specialist's hand book that I turned back to the library when I retired.

The technique is to add up all the bits of pressure drop in your part of the system. With the flow rate and dimensions - and some assumptions about the physical properties of the sewage being pumped, pressure drop can be calculated.

The prop needs to be selected not by size (it'd be 10 inches I think) but by number of blades, twist angle, ... . The manufacturer should have curves for the prop matching head (pressure drop), rpm, and efficiency. Flow rate x pressure drop can be converted into horsepower required. Then divide by the efficiency to get the motor size.

Actually, looking back at this, I'd start with pump manufacturers who sell this equipment. I'll bet some even have 'calculators' on their web sites.

Whatever I've left out (or gotten wrong!) will be corrected by the next poster.

Good luck!

N=Q*H/Et

Q- mass flow rate H-head of the propeller (differential of the total pressure) Et-efficiency of the driver

Correction: H=((P2-P1)total)/density