Choosing your pump|
Which pump do I need?
Before you can pick the best pump for your pond, you need to determine two things:
(1) what flow rate you want
(2) what total dynamic head (TDH) your system requires to deliver that flow rate.
Since the head affects the pump's flow rate, you must know both parameters to properly select a pump.
The exact flow rate you will need depends on many factors including the size of your pond and waterfall as well as the amount of fish, plants and sunlight. Before you can find that pump, you MUST HAVE the head required by your pond system for that flow rate!!!
Head is a measure of resistance to flow. If a pump has a maximum output of 20 head feet, it means it can pump water 20' straight up in the air. If a pump is rated at 50 gallons per minute at 10 feet it means it can pump water up 10 feet and still deliver 50 GPM. As you increase the head, (above the full flow head) you will decrease the flow rate. Therefore to maximize your flow, you must minimize your head. For pond applications the three main sources of head are:
- Static Head - This is the vertical distance you raise the water. To determine your static head, measure from the surface of the pond (vertically), to the highest point in the discharge line where the water is discharged to the atmosphere. This is usually the top of your biological filter, stream, or waterfall.
- Friction Head - As water flows through pipe and fittings there is resistance. The higher the flow rate, and/or the smaller the pipe, the higher the resistance. Determine your overall pipe length, including equivalent length for your fittings. Consult the Friction Loss Chart. Find where the column for your pipe diameter intersects the row for your flow rate and read your friction loss per 100' pipe. Use large enough pipe to minimize this friction loss. It is usually best to keep your friction losses to around 5 feet/100' of pipe.
- Pressure Head - Any additional pressure required by filters, UV lights, foam fractionators, spray nozzles, etc. must be calculated. Determine the pressure drop across each device. The conversion is 1 psi = 2.31 head feet. (ie. a 5 psi drop across a filter = 11.55 feet.) To determine your TDH (as represented on pump curves and tables), add your static head, friction head and pressure head. Now that you know your flow and head, you can select a pump that provides this performance, and does so efficiently.