How do pumps work?Most pumps that are in use for Ponds and Water Gardens are known as centrifugal pumps. These use an impeller which has spinning blades that rotate causing the water to be pushed through the outlet of the pump. The design of the impeller and the speed of the motor varies but technically all centrifugal pumps basically work the same way. As the water enters the front (input) of the pump it comes in contact with the spinning blades or vanes on the impeller which pushes the water through the output or volute and through the tubing or pipe. Pond pumps are measured by the volume of water they produce in gallons per hour (GPH) while pool pumps typically are rated in horse power (HP)or the size of the motor itself. The pump produces pressure which is usually expressed in feet of Head which is the maximum height in feet that a pump can push a column of water. Naturally, it is easier for a pump to push water one foot high than to push it ten feet high. The flow varies depending on the height. Pump flow is measured in
gph at a given Head height, such as 1000 gph at 1’of Head but as the Head increases it may drop to only 750 gph at 5' of Head.
Although a pump may produce 1000 gph you will need to know both the gph your pond requires and the head height of your waterfall in order to choose the right pump. In that way you will be able to select the pump that gives you the correct flow you want at the Head Height you will need. This information is typically supplied by the manufacturer.