Page 64 - Koi Net - On-Line Koi Magazine - Issue 36

If the return is on the pond edge, you will easily have The higher this head height, the less water comes out of
an inch or a few cm which is very little, and a small the hose or pipe behind the pump. As can be seen in
consideration here, the returned water should flow by the diagram opposite, this has a huge impact. (I have
gravity back into the pond and not have to travel chosen the images purely for illustration because this
upwards which would increase the head height and graph is slightly different for each pump.) The example
may stop the water returning to the pond via gravity. pump that can move 13,000 litres per hour (Qmax L/h)
But in general, if the water is delivered from the pond without resistance, falls back to about half at about
to the bottom of a filter then there is no increased head 7,000 litres per hour at 2 metres of head height. The
height provided the water level in this filter is equal to pump uses the same amount of energy (watts) to do
that in the pond (Pump-Fed System). this. Now 2 metres is already a very large waterfall and
high trickle filter but even at 1 metre this is in the same
A waterfall clearly has a head height and thus causes example up to 9,500 litres. So do you have a pond of
losses. You pump water up and from there it falls back 12m³ and do you want to pump it around once an hour?
into your pond to the water level in your pond. A trickle Then decide what your head height will be. Purely from
filter can be seen as a kind of waterfall and therefore a WHAT IS THE the head height, this pump will work with a gravity
filter with a large head height. What is the impact of IMPACT OF system, so without a head height loss, but if you simply
this head height on the amount of water a pump can put your filter next to a low pond without digging in the
move? Well, a lot. THIS HEAD filter thereby creating a head height loss of 1 metre, then
HEIGHT ON you won’t pump enough water around with this pump.
THE HIGHER
7m 1,000 l/h THE AMOUNT 7
THE HEAD OF WATER A Hmax (M) 3500 5000 6500 8000 10000 13000 15000 18000 20000
HEIGHT, THE 6m 2,000 l/h PUMP CAN 6
LESS WATER 5m 3,000 l/h MOVE? 5

COMES OUT
4
OF THE HOSE 4m 4,000 l/h
OR PIPE 3
3m 5,000 l/h
2
2m 6,000 l/h
1
Qmax (L/h)
1m 7,000 l/h
0
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

Resistance
Now there are a few more factors to consider here such
as pipe resistance and pump design. Looking at
resistance first, every metre of pipe or hose and at
every bend the pump encounters more resistance
which makes it more difficult to pump the same amount
of water through the pipe (and filter) which cannot be

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