Alex's posting was spot on.
You need to consider the nature of the pump design for the application you have. While there are many, many types of pumps, there are a specific few that might have merit depending upon your situation.
Three issues are relevant there in terms of pump design.
THE MANNER OF PUMP SUCTION
I believe i understood that your pump was getting its water directly from a pond.
Is this correct?
A Will your pump be inserted below the water line of your supply under all conditions?
B Will your pump have to "suck up" water from the water line?
C Is you water human drinkable quality or will it have particles (say, sand or silt)? Affects pump clearances and internal materials. Centrugal pumps are normally not "in the water", but submersible pumps are. They don't go dry when a "self priming" style is selected.
INTERPRETATION OF PUMP CURVE INFORMATION
If you look up pumps, you might want to start at the Gould's pump catalog.
Once registered, you go for the pump selection, selecting all types and all speeds, and the flow rate (5 gpm) and the head (102 ft) and you will get a series of pumps.....
Three without flags
MULTISTAGE 1HMS 3500 1HMS3 144 32 2 0.568-
MULTISTAGE 1SV_8-16 3450 8 Stage 3 HP 365 27 2.24 1.62 --- ---
MULTISTAGE 2HMS 3500 2HMS3 126 30 3 0.53 --- ---
if you examine the two whose hp rating is about 1/2 HP (the 3 hp is too much for what you need)
Then you can exanine the pump curve.
Lets say you are looking at the 2HMS3 (and later the 1HMS3)
You can use the pump curve in several ways... from the design point of 102 ft and 5 gpm, you could go up to see how much head it could provide at 5 gpm (roughly 127 ft by my eyeball) or, if you had a presure drop of only 102 feet, move horizontally to the right for a flow of someting like 20 gpm.
But what is the REAL flow? Well, there is something called a system curve, which Alex described. As the flow goes up the pressure loses increase (that is the HEAD, in feet, increases). The pump curve goes from upper left down to lower right. The system curve goes from lower left to upper right ....So,if we plotted the system curve over the pump curve, the intersection is the operating point.
You can google/ look up Hazen -Williiams equation and caclulate your system flows, if you're careful. Follow Alex's lead. For the design conditions here, we get about 6.7 gpm at something like 125 ft of head.at that point, we look down on the pump curve and note the hp rating and the NPSHr. Its higher than the .53 hp in the selection table... but far less than 1.0 hp... also your NPSHr is only 3 feet .. I'll let Alex describe that ....
Do this for the other pump. You may well want the one with a larger head capacity .... This is all part of the process...
best fortune
owhn
