Non-pressured filters have a non-airtight lid, allowing atmospheric
pressure to enter the top area of the filter. The water exits
these filters and returns to the pond by gravity flow. Some can
be gravity fed, most are pump fed. A few are gravity fed, pump
return. The plumbing must proceed away from the filter in a downflow
configuration. As such this type of filter must be located in
the landscape at a higher elevation than the point at which the
returning water exits the final plumbing.
Upflow or Downflow:
types of non-pressurized, gravity return filters are currently
used. One uses a simple plumbing exit port which is connected
to the return pipe plumbing. The second has a waterfall weir
(spillway return) plastic trough which spills water into a headwater
area to a waterfall. Both of these non-pressurized style filters
can be of an upflow or downflow configuration, depending on the
position of a baffle inside the filter itself. The "upflow"
or '"downflow" aspect refers to the direction of water
flow through the filter. Based on our experience, we prefer the
upflow type. Any time you cause the unfiltered water to flow
against gravity you will always accomplish the dropping out of
solid waste, thereby separating the waste from the water before
it gets to the filter media.
filters are an in-pond non-pressurized type which are typically
used on beginner ponds. They rest on the floor of the pond and
have a submersible pump attached to them. The suction side of
the pump is connected to the filter box which houses filter media.
Unfiltered pond water is drawn through the media under the suction
pressure of the pump. These filters are the highest maintenance
type. They bog the pump over time since they work on the suction
side of the pump. Since they are in the pond, they require physical
removal to clean. Its best use is with very small, first time
ponds or better yet, for short term holding tanks.
non-pressurized filters in general for the following reasons:
1) They typically require less pump horsepower to operate than
pressurized filters because they are not required to force water
through the filter. 2) You can easily see and therefore evaluate
the condition of the media. 3) Power outages do not cause rapid
depletion of dissolved oxygen in the filter because the media
is exposed to the atmosphere. Non pressurized filters can take
a little more time to set up than pressurized filters. They also
have somewhat limited location possibilities in the landscape
due to their gravity return nature.
filters are relatively simple to install. Most use plastic sphere
or other similarly shaped plastic media which semi-floats in
the upper portion of the canister during filtration. Pressurized
filters must be connected to the discharge (output) side of a
pump. Since water is forced through them, they require more horsepower
to operate and often more power to backflush. Some require additional
maintenance air blowers to assist in the backflush mode. All
spend more of the pump's pressure to operate than non pressurized
filters. All vastly benefit from the use of a prefilter. None
allows for easy and complete viewing of the media without opening
the filter, requiring some simple tools.