The Principle Of Operation Of The Fish Tank Filter

The right choice of Fish Tank Filter is a difficult task, the solution of which largely depends on the successful maintenance and breeding of aquarium fish. Accordingly, it will not be superfluous to familiarize yourself with the problem ahead of time and decide on the choice of filter even before buying an aquarium, which in the future can considerably save time and money. Since the wrong choice can turn into spending on the purchase of another filter, and in the worst case – other fish.

First of all, what is an aquarium? An aquarium is an artificial biotope, a practically closed ecosystem whose inhabitants, as a rule, are not found in nature in such quantities in such a small volume of water. Because of this and a number of other reasons, it does not operate, or the mechanisms of natural purification are not effective. Consequently, all responsibility and control over the maintenance of optimal conditions for living aquarium fish, is entirely assigned to the owner of the aquarium. Including using filters. However, no filter eliminates the aquarist from the need to replace part of the water with fresh (with varying frequency). Water is a universal solvent. The waste products of fish, plants, microorganisms that do not settle in the form of an insoluble crust in a tank are dissolved in water and are not removed by the filters available to aquarists. Therefore, do not forget to clean the aquarium and regularly replace part of the water in it. This will not only positively affect the health of your pets, but also significantly reduce the number of unwanted aquarium microflora.

It should be remembered that there are types of aquariums that do without filters at all, for example, the so-called Dutch aquariums. In them, the aquarium plants take over the cleaning function. Perhaps you choose such an aquarium, then there will be no special need for a filter. On the contrary, tsikhlidniki manage with a small number of plants, or without them at all. In this case, a good, high-quality filter is needed. Nowadays, a large number of various cleaning systems are known, based on pump or airlift method of creating water flow. Filtration systems, in turn, are conventionally divided into many groups, reflecting the type of construction, principle of operation, filtration, and the methods of creating water flow mentioned above. You can find filters: both external and internal, biological and mechanical, there are suspension filters and built-in, as well as standing on the ground. Often with the filter integrate additional devices to perform such functions as – heating, aeration and so on. Often they are connected to ultraviolet lamps.

Remember that it is better to give preference to such a model, which, based on the volume of your capacity, had some margin of performance. The power of any filter can be easily reduced, but it will never be possible to raise it above the one stated in the technical passport. Do not be lazy to do the calculation of the power or volume of water – an extra twenty to thirty percent, this is not money thrown away to the wind, but your insurance against problems that always arise unexpectedly.

The figure shows a hybrid scheme of the airlift filter. 1. Filtering material; 2. Air supply from the compressor; 3. A tube through which water is “sublimated” by air.

The principle of operation and the device aerlift filter

To begin, consider the airlift filter device. Airlift, also known as airlift, gas lift (from English aero – air and lift – lift), is a type of jet pump. The principle of operation is to use the lifting force of the air. In the tube installed vertically in the aquarium, air from the compressor is fed into its lower part. Sprayed through a nozzle, it forms a mixture with water similar to an emulsion (water / air mixture), which, being lighter than water, rises upward through a tube, displaced from below by the pressure of aquarium water. Water bubbles also contribute to the rise of water, which entrains the water mass with its quick upward movement. Note that the function of aeration (air saturation) of water is incorporated in the device itself and there is no need to install an additional aerator.

If desired, a filter is easily assembled on the basis of such a pump from scrap materials. For a simple device, it is enough to put a foam cap on the lower end of the branch pipe. In addition, you can make a simple hinged external filter and organize water purification at the airlift exit. To this end, a container with a filler is attached to the top of the tank so that the water leaving the airlift passed through the filtering material and then flowed into the aquarium. Such a construction can be modified by replacing the filter material with expanded clay or pumice stone and planting fast-growing plants on its surface. The root system of plants, which has a large surface area, will play the role of a filter, taking substances dissolved in it from the water. This filter is an example of hydroponics, and the filtering system with the participation of plants can be attributed to biological filters, phyto filters.

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The advantages of the airlift filter include simplicity in operation, disadvantages — relatively low productivity and, as compared with the pump filter, tight restrictions on the height of water rise. With the help of airlift, tilting the outlet tube at an angle to the water, you can create a small movement of water in the aquarium. However, do not abuse this, because by placing the handset horizontally, we will greatly reduce the already poor performance. Such filters are convenient for small volumes. If there is a need to raise the water to a considerable height or to install a filter in a large aquarium, it is preferable to use a pump.

The Principle Of Operation Of The Fish Tank Filter

Photo airlift filter. The spray gun, located at the bottom of the plastic casing, is filled with filtering material. The air, leaking through the drainage, carries water along with it, while the dirt lingers in the filter (photo by Dr. David Midgley)

The principle of operation and design of pump filter. Characteristics of the centrifugal pump

There are two types of pump filters: internal and external. Often they enclose a pump and one or more compartments for fillers in a single design. In addition, some models are made in the form of independent blocks. These include a canister external filter, where the pump is lowered into the case and continuously pumps water into the aquarium, or in the case of a canister located above the water level, the pump can be installed directly into the tank and supply water to the filter, from where the latter flows by gravity back into the aquarium.

Consider in more detail the device of our pump. Most often, centrifugal pumps combined with an electric motor of a special design and constituting a single unit are used as an Fish Tank Filter pump. Metallic conductive and magnetic elements of the engine are molded with a polymeric material, which makes it safe to operate the device in an aggressive aquatic environment. Another more modern version of the impeller is based on heat-treated plastic, into which, in the form of impurities, magnetic materials are introduced. Structurally, the pump is designed so that the water flow generated by the pump impeller passes through the engine and cools it.

The Principle Of Operation Of The Fish Tank Filter

Internal filter pump (side view). Notation below

The Principle Of Operation Of The Fish Tank Filter

Bottom view

The Principle Of Operation Of The Fish Tank Filter

Pump or head of the internal filter. 1. Sealed plastic case in which the stator is enclosed; 2. Snail-shaped case in which the impeller with blades rotates; 3. Water pressure regulator; 4. Air hose (for example, from an aerator); 5. Ring for mounting the filter; 6. Rotor with impeller.

An alternating electric current, flowing through the stator windings, creates a traveling magnetic field that drives the magnetic elements of the rotor, causing it to rotate. The pump impeller, located in the cochlear case, is rigidly connected to the motor axis. During rotation, the curved blades of the impeller (impeller) create centrifugal force and push the water from the center, where the inlet is, to the circumference. Spinning the water in a spiral, the blades of the impeller create excess pressure of water around the circumference and lowered in the center, where water from the aquarium rushes through the inlet of the power supply tube. On the circumference there is an outlet, through which the water flow leaves the pump.

Why does water flow through an air tube in Fish Tank Filters?

– This is because a high resistance is created at the outlet of the pump. It can be associated with a strong overlap of the water flow regulator, or the installation of a flute.

The main hydrodynamic indicators of pump performance are the flow rate and pressure of water created by it.

Consumption Is the amount of water (in liters) that is pumped per unit of time at a given pressure. It should be remembered that due to structural differences, even with the same indicators of electricity consumed, the ratio of pressure and flow will differ. In the passport data, the manufacturer sometimes in the form of graphs or tables displays the dependence of the flow rate and pressure of the water passing through the pump and filter, on the height of the rise of the liquid.

The movement of water through the pump will certainly generate an increase in its specific energy, called head pressure. This indicator determines the height at which water rises when moving vertically upwards, and, therefore, affects the location of the external filter relative to the aquarium. The pressure, as a rule, is measured in meters or pressure units of a liquid column.

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When choosing a high-performance pump, it should be borne in mind that the maximum flow rate and pressure of water is achieved by its location at the level of the interface between media. Water consumption naturally depends on the height of the rise and will decrease with its growth. During the operation of the filter, filler and the inner walls of the pump are inevitably contaminated, which leads to a reduction in water consumption. The aquarist needs to monitor the condition of the pump, and when loosening the jet of water, immediately begin cleaning. Otherwise, the pump will overheat and fail. All components of the filtration system should be checked and cleaned: hoses, flutes, carbon dioxide flow reactors, the canister and the filler itself (which may need to be replaced regularly).

If you plan to install a filter in your aquarium and make a preliminary calculation, it should be remembered that the practical pressure of the water created by the pump will be somewhat less than the theoretical one. There are several explanations for this. So, due to the design features of centrifugal pumps, not all of the water that enters them experiences the pressure of the impeller rotating blades, which leads to a drop in the speed of water movement near the outlet nozzle. Part of the energy must be spent on the impeller to overcome the inevitable hydraulic resistance of water and friction. Additional resistance to the flow of water due to the structural features of the filters, as well as the presence of any devices that have to be overcome by water. The nominal difference between real and theoretical pressure only increases with time, which occurs due to the formation of mineral and bacterial plaque.

However, the effect of changing the flow rate of water that occurs when it passes through different parts of the system, each of which has a specific cross-section, is used by aquarists to create filters.

Calculation of water velocity in the filter and the method of its measurement

Consider a specific example of an external canister filter consisting of a canister with a filler and hoses that feed and discharge water from it. Due to the different cross-section of the canister and hoses, the flow rate of water will differ, despite the equality of its passing volumes. The flow of water in the hose moves at a speed of several meters per second, and in the canister it drops several hundred times, only a few millimeters per second.

Example:
To simplify the calculation, we neglect the loss of speed and take into account that we are given the actual filter performance at a given height of the water level in the aquarium above the canister, that is, the performance takes into account the pressure of the water column.

Given the filter consisting of a pump and a square canister:
– pump performance is 1 m 3 / hour = 0.00027 m / s = 0.277 l / s

– internal diameter of hoses D = 0.02 m (radius = 0.01 m)

– side of the canister Wк = 0.3 m

– V – volume of water pumped by the pump
Pump performance = V / t = Sш * Vш = Sк * Vк, where Sш and Sк – cross-sectional area of ​​the hose and canister; Vш and Vк – the rate of passage of water through the hose and canister.
Sш = π * R 2 = 3.1415 * 0.01 2 = 0.00031415 m 2
Sc = Wc 2 = 0.3 * 0.3 = 0.09 m 2
Vш / Vк = Sк / Sш = 286,5
Thus, the speed of water, when passing it through the filter, drops 286.5 times.
The speed of water in the hose is Vш = 0.00027 / 0.00031415 = 0.88 m / s
The speed of water in the canister is Vк = 0.00027 / 0.09 = 0.003 m / s
When calculating the water velocity in the filters, it should also be taken into account that the cross-sectional area of ​​the filter is always greater than the cross-sectional area of ​​the filtering material. Hence, the speed through the filter material depends on its permeability (when using a porous, sheet or fiber filters), or on the size of the particles or granules of the bulk filler. In the general case, when the filler is fresh and as permeable as possible, the efficiency of water purification increases with an increase in the ratio of Sc / Sb and Vb / Vc. The low rate of passage of water through the canister and filler provides a more complete transformation of ammonium by nitrifying bacteria, and also allows solid waste to settle in the filter.

The method of measuring the total pressure or flow rate of water by a real filtration system or pump is simple and does not require the involvement of special devices. The easiest way to measure the total pressure with a tape measure. To do this, you need to connect a transparent hose to the pump outlet, then, with the pump on, raise it to a height higher than the head pressure level on the data sheet. We will see how the injected water rises up the hose to a certain height. The magnitude of the pressure obtained by measuring the height of the raising of water in the hose to the water level in the tank from which it falls into the pump.

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Measurement of water flow is performed using a water meter or water meter. If not, the water flow can be measured using a bucket and a measuring glass. For this, for some fixed period of time (for example, minutes), we will flush the water into the bucket. In this case, if we arrange the level of the jet outlet at the water level in the aquarium, we will get the water flow through the filtration system, with a head value equal to zero. In conclusion, we will consider some issues directly or indirectly related to the operation of pumps, affecting their service life. Facts that will not be superfluous to know.

"Beach" pump – cavitation

Cavitation is a physical phenomenon that occurs in a liquid when it boils due to a change in pressure. Applied to pumps, a phenomenon occurs at the fluid inlet to the pump impeller. In that case, if the absolute pressure of water is equal to or less than the vapor pressure at a given temperature, the water begins to “boil”, which results in the flow breaking and pumping termination. In the place where the pressure is less than or equal to the saturated vapor pressure, the release of gases and water vapors dissolved in water with the formation of microscopic bubbles. Bubbles are addicted to streams of water in the area of ​​high pressure, where they collapse, causing mechanical damage. The working areas of the pump get microscopic damage from collapsing bubbles, which, with prolonged exposure, leads to rapid wear of the pump and its failure (mainly, the blades of the impeller). The occurrence of cavitation, when the pump is operating, is accompanied by a significant and sharp decrease in efficiency.

Cavitation is accompanied by characteristic noise and vibration of the pump and is characteristic of any pump filters, both external and internal, with the connection of aeration at the filter inlet.

Characteristic noise may also occur for another reason, signaling that the pump cannot pump water, because an airlock has formed in the hose of the external canister filter or simply a bend through which water flow is extremely difficult or impossible. As a rule, this problem arises because of an unnecessarily long hose that, when not fixed, falls below the level of the pump outlet.

Manual head pressure control

In filtration systems, an aquarist, for his own purposes, can change the water pressure. In particular, this is done to regulate the speed of water, but only downwards. To change the head you need to know the location of the pump – whether it is worth it before or after the filter. It works mainly with external canister filters, which are equipped with several regulating taps. Depending on its location relative to the filter, the pump will create a pressure in it equal to its head, or a vacuum also equal to the head. Pressure is created by the pump if it is before the filter, and vacuum is if the pump is located after the filtration system.

If we close the inlet tap, it will reduce the amount of water passing through the pump and reduce the vacuum (negative pressure). As a result, the water pressure at the outlet of the filtration system will drop and the pressure will decrease.
If we use the outlet valve and cover it, we will achieve an increase in pressure at the outlet of the pump (not the filtration system). The amount of water passing through the filter will decrease, and the amount of vacuum in the module will also decrease as a result.

It should be remembered that the use of undocumented modes can lead to overheating or the pump outage. Prolonged operation of the pump in such modes, lead to overheating of the stator, which entails overheating of the windings, with all the "ensuing" consequences.

Aggressive environment. Recommendations for materials

Decaying remains of feed, plants and fish excreta themselves – a source of nitrogen compounds (nitrates, nitrites, ammonia, etc.), phosphorus and sulfur. They are also chemically active and can cause corrosion. Entering into chemical reactions with water, gases dissolved in it, aquarium sludge, they can form organic and inorganic compounds (including acids) contributing to the destruction of parts, both from metal and some types of plastics.