How to calculate GPH for a pond or fountain pump

Measuring gallons per hour

     As a pump pushes water higher in a vertical pipe, gravity creates increased resistance. Therefore the gph of a pump decreases as the discharge height (known as head or lift) increases. The resistance created by forcing water to flow horizontally 10 feet is roughly equivalent to the effect of lifting the water 1 foot vertically. Of your pump forces water 20 feet horizontally, for example, that translates to 2 feet vertically. Knowing this gph at a designated point tells you whether the pump can deliver the quantity of water needed to properly operate a waterfall with the planned spillway’s width, depth, and height as well as its distance from the pump.

     Manufacturers list how many gph a pump recirculates at 1 foot of lift and at other heights. If the height you need is between two listed heights, estimate what you could reasonably expect. For example, of you need 300 gph released 3 feet of head. That same pump might recirculate only 200 gph at 6 feet of lift. It would not be powerful enough to recirculate 300 gph for a 6-foot-high waterfall.

     To build in a margin of error, measure the water distance vertically from the pump, not from the water’s surface. One way or another, avoid skimping on gph. When determining the proper flow rate for a waterfall or stream, figure 150 gph for each inch of spillway width. This rate provides a ½ inch-thick sheet of water over the falls. You’ll also need to know how far the water must travel horizontally in the pipeline. Remember that each 10 feet of horizontal distance creates about as much resistance against the pump as 1 foot of head. Consider a pump that must force water 10 feet in a pipe across the pond bottom and then 5 feet up the pipe to the release point in the waterfall. This is equivalent to a 6 foot head.

     Although some variation exists from rated gph capacity, pumps do not operate at more than their rated gph capacity for each rated height. To be safe, purchase a pump with grater capacity than estimated need. While a pump’s gph cannot be increased, it is easily reduced using a valve on the pipeline or a restrictor using a valve on the pipeline or a restrictor clamp on the flexible tubing that limits the flow of water from the pump to the discharge point. Some pumps come with a built-in valve on the discharge. Any restriction you add should be placed on the water line only after the water exits the pump – never before entering the pump. Pumps easily withstand this restriction. It has the same effect as making the pump push the water higher in the line. For more helpful information please visit us at http://www.discount-pumps.biz/choose-pond-pump.htm