Selecting a pump can be confusing.
It is critical that the proper pump is chosen to ensure
longevity and trouble free performance. Following are
several things to keep in mind when selecting a pump:
How much volume of
water flow do you need?
It takes approximately 36 gallons per minute to make a
waterfall or stream 1' wide x 1" deep (1" deep water is
considered an average depth for residential applications).
The first step in determining how much water you need is to
multiply the width of the waterfall or stream in feet x 36 =
gallons per minute needed to make 1" deep of water.
Example: A 3' wide stream or waterfall would need 108
gallons per minute to be 1" deep.
3 feet times 36 GPM = 108 GPM
This determines how much
volume you need. Next, determine how much head (lift)
there is from the surface of the pond to the top of the
waterfall. On a small, simple waterfall the vertical lift is
all you need, however on large applications you also need to
factor in friction loss from the pipe as well as each
fitting to get the total head.
This determines head
pressure.
Now that we know water volume needed and the head height it
is needed at, it makes selecting a pump much easier.
Start by
looking at our chart This chart lists all of our popular
submersible pumps on one page. Look in the box on the right
side of the chart - find the column of head closest to your
application then follow that column down until you find a
pump that delivers the gallons per minute (GPM) you need.
External pumps
Using an external pump raises several questions regarding
proper pump selection.
Self Priming - A
self priming pump can sit higher than the water level being
pumped by a few feet (depends on the model) and will
displace the air in the suction line to prime itself.
Non Self Priming -
These pumps must either sit below the water level being
pumped or must have a check valve installed at the end of
the suction line to keep water in the system after being
primed the first time.
All external pumps are
designed to push water, not pull it. This means the pump
should sit as close to the pond as possible!
Proper plumbing is
important!
Your pump can only perform as well as your plumbing system
allows it to! Very often contractors use pipe that is too
small and then cannot figure out why a larger pump doesn't
give them more water.
Always size your plumbing
for the amount of water you are pumping regardless of the
outlet size of the pump!
Maximum
water flow for pipe sizes:
1"= 25 GPM 1 1/4" = 45 GPM
1 1/2" = 60 GPM 2" = 90 GPM
3" = 225 GPM 4" = 350 GPM
6" = 700 GPM 8" = 1500 GPM
10" = 2500 GPM
Fittings can
also reduce flow - 90º elbows should be avoided if at all
possible (use two 45º elbows).
Proper electrical supply
is critical
Inadequate power supply is one of the biggest contributors
to reduced pump service life, poor performance and premature
pump failure. Low voltage caused by undersized wiring,
having too many items running on the same line and not
double checking the voltage/amp draw once the pump is
operating are common mistakes that lead to problems. All
pumps need a certain amount of back pressure to operate
correctly. Often times a ball valve is needed on the outlet
side of the pump to create the needed back pressure. Without
this back pressure the impeller will pump more water than
the motor is rated for creating high amp draw and excessive
heat. This will lead to shortened motor life and premature
failure. By closing the valve a small amount, back
pressure is increased and the motor operates within its
designed service factor. |
