Home' Splash Magazine : SPLASH Dec-Jan 2016 Contents Suction outlets
In an accessible catchment pond (< 300 mm deep): AS
1926.3 requires approved suction covers be installed.
Leaf problems can be largely overcome by using multi-
ple suction outlets.
Where, for aesthetic reasons, water is required in a
catchment pond that would otherwise gravity feed to
a remote balance tank, this can be achieved by having
the water flow out through several 80mm plus diameter
stand pipes set to the desired water level.
In an inaccessible catchment pond (>300 mm deep)
and balance tanks: In these ponds I prefer that the
outlet pipes remain open – no covers. This is mainly to
assist in the removal of debris to the pump H & L pot
or a leaf canister.
The suction line
When a pump is located at a higher level than the
catchment pond or balance tank it is drawing water
from, it is necessary to install a foot valve or non-return
valve (NRV ) as low as possible in the line.
I discovered many years ago that a single NRV could
get held open by a leaf or other bit of debris passing
through the valve at the time the pump shut off. When
this happens it is possible for the water in the pool
to syphon back to the pond or tank, overflow it and
generally create a real mess. My solution has always
been to install two such valves quite close together as
the chance of both being held open by a leaf at the
same time was very remote. So far it has worked well
but the day may come when the valves wear out with
The NRVs of course enable and maintain prime
to the pump so at least one of them can’t be done
away with. But the best protection from a syphon
accident is for the filtered water return line to
be looped just above the pool water level with a
vacuum breaker device at the top of the loop. This
means that if the NRV was to fail only the water
in the pipes would fall back to the pond or tank as
the breaker would open to atmosphere and prevent
I developed my double NRV system because in
many cases I could not find a place for the vacuum
Gutter gravity flow outlets
Gutters should have several outlets into a manifold
pipe. The outlets will exit more quietly if they are
horizontal through the side of the gutter. It is generally
not necessary to slope the actual collection gutter unless
you want to get all the water out in a hurry through one
large outlet at one end.
Gravity flow pipes
There are tables and charts available to size gravity flow
pipes. In most domestic pools with some variation for
the distance and slope involved, 80mm or 100mm pipe
is sufficient. Pipes should have a minimum 1-in-50
slope to the balance tank. Where a lesser slope is neces-
sary a larger pipe diameter is required.
Falling water is cooling water and every vanishing edge
pool has some falling water, some more than others.
When a vanishing
edge goes wrong
The pool is a good illustration of a classic vanishing edge design fault.
It is a 25m pool with a 14m vanishing edge where the pool is only 2.5m wide.
Such a narrow pool does not have the surface space for the disturbed water
from lap swimming to at least partially dissipate prior to finding its way over
the edge. When the owner swam laps, most of the overflow water would
land up to 900mm away from the pool edge, well past the 300mm wide
The builder was fortunate that the owner was happy to have and pay for, the
installation of a glass panel across the whole width to ensure that the water
dropped into the gutter.
With the entire overflow going into the balance tank under the plant room
that is hard against the end of the pool it then became evident that the
tank was too small – water was going in faster that it could be filtered and
sent back to the pool. The excess water went out an overflow pipe and was
thus lost from the system. There was then insufficient water in the tank to
replace the displaced water from the pool.
The next solution
The fully tiled pool was emptied and two 50 mm pipes were core drilled
through the end of the pool into the equipment area. A second suction line
was installed in the balance tank and the pipes were then connected to a
second 2hp pump that simply pumped all the excess water directly back into
the pool. Because this pump was not needed unless the pol was in use it
was controlled by a specially adapted Water Witch water leveller to turn on
the pump when the water rose in the tank and off when it fell. The reverse of
a normal water leveller.
This was a case of having to think outside the box. It all worked perfectly, the
pool owner was and remains happy with his pool.
40 SPLASH! December 2015/January 2016
Links Archive SPLASH Aug-Sept 2015 SPLASH Feb-Mar 2016 Navigation Previous Page Next Page