Let's go back to the example pond from earlier in the article.
Assuming a volume of 1000 gallons (3784 liters), a static head
(waterfall height) of 2 feet (.6 meters) and frictional loss
due to tubing, fittings and filtration equipment of 8 feet (2.4
meters) of head, you have 10 feet (3 meters) of dynamic head.
The 2400 GPH (9082 LPH) pump (green) might seem like a good choice
for your pond. However, its performance curve shows that the
2400 GPH (9082 LPH) pump only moves roughly 1300 GPH (4920 LPH)
at 10 feet (3 liters) of head. Furthermore, the 3600 GPH (13623
LPH) pump (blue) produces a flow of approximately 2500 GPH (9461
LPH) at 10 feet (3 meters) of head.
Armed with this information it becomes clear that the 2400
GPH (9082 LPH) pump fails to produce the desired 2000 GPH (7569
LPH) flow. The 3600 GPH (13623 LPH) pump produces more than your
requisite 2000 GPH (7569 LPH), so it becomes a candidate. Remember
that this chart illustrates the performance data for just one
pump manufacturer, highlighting the importance of this data for
any pump you consider. Often, pumps from Manufacturer X display
a significantly different performance curve than those from Manufacturer
Shopping online or at water garden supply stores, you find a
tremendous selection available. Besides flow rate, you must choose
between a 110 or 220 volt model, an external or submersible installation
location and direct drive or magnetic (mag) drive propulsion.
Picking the pump voltage is a good starting point. While you
might already have an outdoor 110 volt circuit, it may be advisable
to upgrade to 220 volts. The 110 volt pumps offer the best combination
of price, operating cost and ease of installation for low to
medium flow (100-7500 GPH) installations while 220 volt models
excel with high flow rates or when a situation would otherwise
call for multiple 110 volt pumps. Speak with a licensed electrician
about what type of circuit you have or can install for your feature.
Another key pump consideration is its location. As the name
implies, external pumps operate outside of the physical confines
of the water garden. They typically appear in large water features
or with higher end koi ponds and are making inroads into traditional
EPDM liner ponds. Quite often external pumps (fitted with basket
strainers to capture large debris) connect directly to bottom
drains and feed vortex filters or settling chambers as they move
water to the filtration system. Some skimmer designs include
provisions for integrating external pumps.
One reason external pumps are growing in popularity is easy
access for maintenance. Being outside of the pond greatly simplifies
cleaning and removing debris. For physically challenged individuals
this fact alone makes external pumps attractive. In addition,
because external pumps consist of a separate power unit and propulsion
unit, manufacturers can "custom make" a pump to fit
your needs. The power unit may work with either a 110- or 220-volt
circuit. Diverse impeller designs enable a performance curve
closely matching your desired flow rate. From a safety standpoint,
external pumps greatly reduce the risk of electrical shock to
Nevertheless, external pumps do have some disadvantages. External
pumps frequently cost more than a submersible pump with the same
flow rate. In order to achieve the operating savings they offer
you need an electrician to install a 220-volt circuit to your
pond area. Hiding and housing the pump in a pond setting can
be challenging. Noise can be a downside to external pumps. External
pumps may need priming before use, which is problematic for those
who frequently shut down the pump. Finally, in cold climates,
winter operation is troublesome because their exposed plumbing
is subject to freeze damage.
While external pumps continue to gain acceptance, the great
majority of water garden pumps are the submersible type. Don't
confuse submersible water garden pumps with sump pumps. True
submersible water garden pumps are engineered for the rigors
of the pond environment and include safety features to protect
humans and wildlife. Submersible pumps sit on the pond floor
or in a skimmer.
The chief advantage of submersibles centers on convenience.
Submersibles are easy to plumb, require no special wiring and
need little care other than cleaning, making them especially
friendly to new water gardeners. Furthermore, submersibles usually
cost less than a comparable flow rated external pump and are
widely available at water garden supply stores.
Clogging is their chief drawback. Being in the pond, they
risk sucking up leaves, twigs, stones or other debris. Although
easily remedied, a clog may lead to pump damage or even failure
if not cleared in a timely manner. Housing the pump in a skimmer
is not always foolproof. The skimmer basket or net can clog,
cutting off the water supply to the pump. Wildlife (usually frogs
or toads) can block the pump inlet and stop the pump. The life
span of submersible pumps is sometimes an issue, especially with
the cheapest models. The 220 volt models yield a longer life
than 110 volt models. On average, external pumps tend to last
Classification of pumps can further be based on the method
used to propel water. Direct drive and magnetic drive pumps reflect
different engineering approaches to pumping water. Direct drive
refers to a copper-wound armature that spins when current is
applied, and rotates a shaft and the impeller. Water is drawn
in, and then expelled through an output port to the filter or
waterfall. Direct drive pumps mirror the technology found in
most common electrical devices like vacuums, blenders and hair
The more popular type, direct drive pumps are relatively inexpensive
to produce. They provide a good flow-to-operating-cost ratio
and their performance curves usually best those of magnetic drive
pumps. Because the technology has been around for so long, direct
drive pumps have numerous adaptations for almost any water gardening
chore. As you research pumps, notice that the biggest and most
powerful pumps in the market are direct drive units. Manufacturers
continually improve performance, reliability and efficiency.
The main enemy of direct drive pumps (external and submersible)
is heat. Since the units contain brushes, bearings and seals,
the potential for failure greatly increases when the pumps operate
at high temperatures. Most often, pumps fail due to running dry
(low water situation), cavitation (air bubbles in the water),
or running too close to their shutoff limit (too small a pump).
Even though pump failure is commonly due to a small internal
component, replacement is more cost effective than paying for
repairs. While the technology is tried and tested, many argue
that direct drives have reached a point of diminishing returns
and in an environment of increasing energy costs, they are simply
becoming too expensive to operate.
This desire to lower operating costs led to additional research
and the design of magnetic drive pumps, or mag drives. Mag drives
consist of an epoxy sealed electromagnetic coil with a hollow
central cavity. A magnet with an attached impeller shaft sits
in the cavity and spins when current is applied. Like direct
drive pumps, water is pulled in through the inlet and expelled
through an outlet port.
Since mag drives use no bearings, seals or brushes, they have
a greatly reduced failure rate due to wear and friction. The
impeller assembly is the only moving part and can easily be replaced
if damaged. Because of design differences, mag drives are more
compact than direct drives. They dominate the market for low
flow pumps, being especially well suited for statuary and tabletop
water features. Of course lower energy consumption is their claim
to fame; mag drive manufacturers claim operational costs about
half that of a comparable flow direct drive pump.
However, the main knock against mag drives centers around
lack of power and poor performance in higher head applications.
The pumps actually perform quite well, but installers must pay
close attention to the performance charts to make sure the pump
is right for the job. As mentioned, mag drives typically flow
lower volumes as head increases compared to a direct drive unit.
Currently mag drives are only offered up to 10000-GPH (37843-LPH)
flow rates, making a limited selection.
Another complaint about mag drives involves impeller damage
from debris. Whereas most direct drive pumps easily handle sucking
up leaves, twigs and even small stones, mag drive impellers may
be jammed or broken by such debris. Many mag drives come equipped
with foam pre filters, but these are commonly discarded due to
a tendency to clog and required frequent cleaning.
Given today's wide choices of pumps and a well thought out
design and construction plan, you will find a pump suited to
your needs. Keep in mind that pump technology is constantly evolving.
Even as mag drive pumps gain in popularity, new products are
on the horizon.
One of the most promising pumps is an adjustable flow pump.
These innovative programmable units enable you to adjust flow
based on the time of day, the season of the year or even during
feeding times. Not only does this save on operational costs,
it opens up a completely new realm of design possibilities for
creative water gardeners. Innovations are essential to our hobby,
especially in light of the ever-growing attention paid to conservation
of our natural resources. Water gardens reflect our attempt to
recreate nature; anything we can do to preserve the environment
As a final thought on pumps, seek the best quality pump you can
find. Price is not always the best indicator of pump quality,
so wade through the marketing claims and do your research. The
warranty period, availability of replacement parts and recommendations
from other water gardeners should influence your choice. Avoid
installers who use a certain brand pump simply because it comes
with the "kit" or "system" they install.
Nothing ruins the enjoyment of a water garden or water feature
quicker than a failing pump, even if it is covered by a warranty.
I have always been a strong proponent of doing business with
a local water garden supply store; regarding pumps, I cannot
stress this enough. Those bargain pumps at the big box store
may be priced right but are certainly not a good value in the
end. I have witnessed piles and piles of failed pumps from a
well-known and "reputable" aquascaping supply company
that supplies installers all over the country.
Why do unsuitable pumps keep finding their way into our water
gardens? Simply due to our own lack of diligence and willingness
to seek out the information readily available to guide our purchasing