Pump Selection
Proper pump sizing for a pond or fountain is crucial.
Too small of a pump will not only produce a disappointing show, but may
also not circulate enough water to keep the pond clean and oxygenated.
Pump output can generally be reduced with a valve or constricting clamp
up to 25% if necessary, so it wiser to choose a slightly overpowered pump
than one that is too weak or only just adequate. With this in mind, a pump
can be selected using the following guidelines:
The required Head must
first be calculated. Head equals the total vertical distance between the
pump and the highest end (outlet) of the system piping.
The rated maximum Head of the pump selected should
always be greater than the Head required. At maximum head, the pump will
only produce a trickle.
The volume of the pond can be estimated by dividing
it into one or more regular geometric shapes, the volumes of which can
be calculated as follows:
· Volume of a cube = length x width x height
· Volume of a sphere = 4/3 x radius squared
· Volume of a cone = 1/3 x radius squared x height
· Volume of a pyramid = 1/3 area of base x height
· Pond volume in liters = Total cubic centimeters x 0.001
· Pond volume in gallons = Total cubic feet x 7.48
· 1 centimeter water depth = 10 L per square meter
· 1 inch water depth = 0.62 gallons per square foot
The pump's Flow Rate at
the required Head (as shown in the pump's performance charts) must be equal
to or greater than 1/2 total volume of the pond or sequence of ponds.
The pump's stated Maximum Flow Rate is typically
the Flow Rate that is achieved at 0 feet of head (straight out of the outlet),
a situation that will never occur in a pond, and therefore should never
be used as a measure when selecting a pump.
The minimum Flow to achieve
1/8" - 1/4" of
water rise over a rocky waterfall is 4-9 gpm per linear foot of
waterfall width.
The minimum Flow to achieve
1/2" of water
rise over a clear waterfall is 20 gpm per linear foot of width.
Except in areas where freezing conditions make it
impractical, the pump should always be run continuously, so power consumption
can be significant.
The best choice for most situations
will be a 'true' pond pump. These pumps are submersible and are
typically magnetic drive, consuming remarkably little power.
They are designed for long life at continuous operation. Sump-style
utility pumps will provide greater head at low cost, but power
consumption is much higher, and because these pumps are not designed
to run continuously, the burn out curve is much shorter. Centrifugal
'jet' pumps are usually located in an enclosure outside the pond
and are designed to move large volumes of water.
The use of oil-filled pumps should be avoided, if
possible. Even a 'non-toxic' oil will become a contaminant in the pond
environment if leaked.
The right type of pump for the job will be determined
almost exclusively by head and flow requirements. It is always better to
oversize your pump as output can later be reduced up to 25% through the
use of a valve or a rheostat.
If a filter is being used
(and budget allows), it is generally better to have a separate, solids-handling
pump specifically for the filter with a second pump powering the fountain
nozzle, waterfall, or watercourse.
