FILTRATION MODES

Before starting the construction of a pond, you must determine the filtration mode and three possibilities are available to you: pumping mode, gravity mode and mixed mode. Here are the differences.

PUMPING MODE

The pump positioned in the basin pumps the water into the filter located on the bank: the filtered water returns to the basin naturally by gravity.

Obviously, the pump can be installed dry, next to the pool, but this remains pumping mode!

Large ponds may have several pumps to ensure sufficient flow, always with the aim of returning the water from the pond to filtration.

Pumping mode is the simplest way to consider filtration, a priori, the most economical to install, but not necessarily the best from an energy point of view.

ADVANTAGES OF PUMPING MODE

- Simple and cheaper to make than other configurations.

- Easy to modify, pumping mode is quite flexible

DISADVANTAGES OF PUMPING MODE

- Paradoxically, although this configuration is less expensive to purchase, it often turns out to be more energy consuming than gravity mode because the pump must raise the water above the water line in a pipe which sometimes causes a loss of energy. huge load.

- The essential difference is that the dirt is sucked up by a pump which reduces the size of these particles, thus making filtration (retaining particles) more difficult.

- Particles whose size is larger than that of the pump strainer remain in the pool: this type of pool can therefore only become silted up if regular cleaning is not carried out.

- The sterilizer radiates UVC into raw, dirty water.

- Unsightly, the pump and the pipes are visible in the basin: the filter can sometimes be difficult to integrate into the garden.

- If the pump pipe breaks, the pool can quickly be emptied!

THE GRAVITY MODE

In the gravity type configuration, the water is sucked into the filter, which causes an imbalance between the levels of the basin and the filter: this imbalance causes the movement of water - with dirt - from the basin towards the filter via the bottom drain and the skimmer.

Technically speaking, the water from the pool is not sucked into the pool since the pump draws into the filter: but the water from the pool passes to the filter by the simple physical principle of communicating vessels.

In fluid mechanics, the principle of communicating vessels indicates that a liquid filling several containers, connected together at their base and subjected to the same atmospheric pressure, equilibrates at the same height in each of them.

As our pump draws into the filter, a measurable level difference is established between the level of the filter and that of the basin: the basin which tends to compensate for this imbalance causes the movement of the water.

Noticed ! The gravity mode means that the water passes from the basin to the filter because a difference in level is caused between the filter and the basin. A pump placed in a pumping chamber and sucking through a drain is not an installation in gravity mode!

ADVANTAGES OF GRAVITY MODE

- The essential advantage lies in the fact that the pump draws filtered water, therefore clean, free of particles. These were retained whole by the filter.

- If the basin is well studied, the bottom of the basin remains clean, no siltation and all waste is evacuated towards the filter.

- The entire technique being below the water line, the pump must exert less effort, therefore sometimes enormous energy savings! We will see later that this ultimately simple system can be optimized!

- Filtration can be easily hidden: gravity mode is THE system adopted by most passionate Koi pond owners!

- This configuration allows all possible developments, also in terms of filtration, sterilization, ozone etc.

DISADVANTAGES

- A little more expensive to install, the construction of this type of network requires experience and skill. Either you are a very good DIYer and you need to seek assistance for self-construction, or you need to entrust the construction to a real professional.

- Building a pond based on this concept requires more time and a certain amount of knowledge because improvisation in this area is risky!

THE MIXED OR SEMI-GRAVITY MODE

A mixed filtration system is sometimes used, especially in biological swimming pools: it combines gravity and pumping.

In the example in the diagram above, the pump draws water into a grid pre-filter which is placed at the same level as the basin. An imbalance is created by the pump, between pre-filter and basin, which causes the movement of the water.

Until then, we are in a gravity type configuration.

But the pump pumps the water sucked into the pre-filter - not directly into the pool - but into a biological filter: in the example above, a pressure filter, but it could have been a multi-chamber filter, that would not be the case. changes nothing. As this pump discharges into a filter, this second part of the circuit is therefore in pumping mode.

In the example above, the filter is below the water line, it causes resistance to the passage of water: even if this resistance is low it remains pumping mode.

Another example: the biological filter is now a multi-chamber filter as in the diagram below.

In this new example the filter is above the water line: this is essential because it is no longer a pressure filter and for the filtered water to return to the pool, a large pipe is necessarily required. evacuation which allows this flow.

Note that this type of flow is called gravity flow, hence the confusion...

In itself, the filter does not cause resistance to the passage of water but as it is placed higher, the pump must exert an effort to raise the water: this is the fault of the pumping mode...

The two schemes seen as a whole are therefore based on the mixed gravity/pumping mode.

In the Hydraulics section, we will look in more detail at how to determine the number of bungs/skimmers to install in a basin.

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2024