| Which
water pump do I use? What
will they cost to run?
All modern koi pond pumps are designed
for 24 x 7 x 365 running and most now have very low running costs. There are
however still significant differences between models, so you will need to
know certain details of your proposed system to enable you to choose the
correct pump. In any koi system it is desirable to turnover the entire
contents of your pond through the filter every 2 - 4 hours. So for example if
you are building a 5000 gallon pond, you will need a main filter pump
capable of delivering at least 1700 gallons per hour (5000 divided by 3).
However pump rating are all given at zero head, the height between the pond
surface and the point that water is returned to the pond. The more the head,
the less the flow rate as more power is required to push water 'up hill' All
pumps manufacturers calculate the maximum recommended head for their pumps
and will supply a chart giving the final flow rate at certain feet of head
pressure.
In addition however you must take
into account the pipework layout of your system - the longer the return
pipework and the more bends present, the greater the frictional flow losses
which can occur and the final pump flow can be substantially affected by
these factors. We would recommend a minimum pipe diameter of 1.5"
(38mm) and if the pipe runs exceed around 10 ft, to increase the pipe
diameter to 2" (50mm) to avoid friction losses. Unfortunately there is no
easy way of calculating frictional flow losses caused by pipework but you
should always allow for a minimum of 20% performance reduction caused by
pipe runs.
Taking these factors into account it
is therefore most appropriate to calculate your filter pump requirements based on a 2
hour pond turnover rate, so in the example above, for our 5,000 gallon pond,
we would recommend a pump with a design flow rate of 2,500 gallons per hour.
Even after allowing for head losses and pipework losses this should still give us a final
flow rate of 1700 gallons per hour at least, so that we are within the
guidelines of a turnover rate of between 2 and 4 hours.
If you are looking for a pump to
power a water fall or Venturi, then there are different factors to take into
account. We don't recommend venturis, as they are very inefficient
devices used to pull air into the pond water by forcing the pump to push
water through a restrictive venturi tube. Not only is the airflow
produced usually too small unless the device is placed right at the surface,
but the final pump flow rate can be reduced as much as 2/3rds! -
Yes 2/3rds. This means you will need a much bigger pump to power the system
than required, just to power the venturi. This increase the initial
cost of the pump, the running costs, and importantly will reduce the life of
the pump - not an ideal set up!
Waterfalls are a tremendous idea in
any koi pond, can look and sound fabulous and provide the most efficient
form of aeration. Again however they need a substantial flow rate to
look the part and because of head losses, the pumps need to be fairly
powerful to achieve the desired result. As an example, a waterfall
with a cascade around 18" wide and 3 feet high would need a flow rate of at
least 2000 gallons an hour at the cascade to look good. There is
nothing worse than a waterfall which dribbles water !
The most important thing to remember
with waterfalls and other water features is that it is not only the stated flow rate
which is important, but the wattage of the pump. There is a big difference
between a 2000 galls/hour flow rate @ 95 watts and a pump delivering 2000
galls/ hour @ 220 watts. The former is classed as a water mover, and
whilst excellent for main filtration flow, would not have sufficient power for a
venturi or waterfall where back pressure and head are significant factors.
The 2nd pump mentioned would deliver the rated flow, overcoming back
pressure and would pump up to considerable heights as it is more powerful,
but of course more expensive to run.
We feature a range of pumps for koi
ponds all of which have specific applications, some dry pumps, some
submersible and some dual purpose. You should now however find it easier to
choose the correct pump for your application having considered the facts
outlined above. We would be happy to help by providing a pump
recommendation - just email us at
helpline@koicarp.org.uk |
