The proper pump is the heartbeat of an effective pond system!
Before you can pick the best pump for your pond, you need to determine what flow rate and total dynamic head (TDH) you need. Since the flow rate is reduced by the head it is working against, you must know both of these parameters as well as others to properly select a pump
The exact flow 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. In general, most ponds will operate nicely if you turn the water over approximately once an hour. This means if you have a 4000 gallon pond, you want about 4000 gallons per hour, or 67 gallons per minute.
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 in the air. If a pump is rated at 50 gallons per minute at 10 feet it means it can overcome 10 feet of head (TDH) and still deliver 50 GPM. As you increase the head, you decrease the flow rate, and increase your operating costs. To maximize your flow, you must minimize your head, which also minimizes your operating costs. For pond applications the 3 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, fountain, or waterfall.
- Friction Head - As water flows through pipe and fittings there is resistance. The higher the flow and/or the smaller the pipe, the higher the resistance. Determine your overall pipe length, including adding in the 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 the friction loss per 100' pipe. Use large enough pipe to minimize friction loss. It is usually best to keep your friction loss (per 100 feet of pipe) to less than 6 feet. In other words, once you know the desired flow rate, pick a pipe diameter, or schedule, that will give you less than 6 feet of friction loss per 100 feet of pipe.
- Friction Loss - THIS CHART GIVES FRICTION LOSSES FOR YOUR GIVEN FLOW RATE PER 100 FEET OF PIPE: EXAMPLE; IF YOU WANT 60 GALLONS PER MINUTE, AND YOU'RE USING 2 INCH SCHEDULE 80 PIPE, AND YOU HAVE A 160 FEET OF PIPE, YOUR FRICTION LOSS IS 8.12 x 1.6 = 12.99 FEET OF HEAD. So we would either want to use schedule 40 pipe, or go to 3" schedule 80 pipe.
- Fittings Loss - Now go to the bottom of the Friction Loss page and pick out the number and type of fittings you are using (use the worst case scenario if you have a bypass): Example; a 2" 90° elbow is the equivalent of an extra 6 feet of 2" pipe, so if you have ten 2" 90° elbows you would add 60 feet to your pipe length. After adding the extra feet for all your fittings you recalculate your total feet of head. In this case it would add 60 feet to 160 feet for a total of 220 feet or 2.2 x 8.12 = 17.9 feet of head.
- Pressure Head - Any additional pressure required by sand filters, spray nozzles, etc. must be calculated. The conversion is 1 PSI = 2.31 head feet.
- If our sand filter runs at 10 PSI, that would add 23.1 feet of head to the 17.9 feet required to overcome the friction loss of our pipe and fittings. So now the total pump head is 41 feet without considering the static head. (Notice that the pump head will increase as the sand filter gets dirty and increases the back pressure.)
- Total dynamic head ( TDH) - Add your static head, friction loss head, fittings loss head, and pressure head.
Type of head
Static Head Waterfall 10' - above surface of water
Pipe Loss 2" Pipe 8.12' per 100 feet of pipe
Fittings Loss 6' per elbow 10 2" 90° elbows = 60 ft
Pressure Head Sand Filter running at 10 psi x 2.31
Total Pump head in feet
- Don't forget to add up the equivalent feet of pipe for all the fittings.
- Now that you know your flow and head, you can select a pump that provides this performance, and does so efficiently.
- Performance Curves
Now we know that we need a pump that can handle 67 gallons per minute at 51 feet of head. This information can be found on the performance curves for the pumps.
- Maximum Efficiency Area
We want to select a pump that has these results inside of the maximum efficiency curve area.
- Lowest Operating Cost
If we have more than one pump that meets all these requirements we can then select the pump with the lowest operating cost, i.e., lowest amps or watts.
- Remember, a 230 volt motor will run at half the amperage of a 115 volt motor, but wattage is the amps times the voltage, so we have not gained any cost savings because we doubled the voltage.
- A 2 horsepower motor can cost $2,000 per year to operate.
- Lowest Noise
We also want a pump that is quiet enough to allow us to enjoy our pond. Most manufacturers can supply a noise number in decibels (dB) at 3 feet from the pump. We want the lowest dB possible. We can also mount the motor on rubber noise isolation pads, or shield it with noise attenuating "walls".