Sand Filter

Sand filters purify water by removing particles, producing clean water for pools, and other uses. The following sections provide key details on sand filter characteristics, sizing, models, and optimal pricing for wholesale purchase.

Guidance of selecting a sand filter

Sand filters are tanks made of galvanized steel, fiberglass and steel, which are made cylindrical (and sometimes square) under atmospheric pressure. By purifying (filtering) water, they remove suspended particles in the water such as mud, paint, suspended particles and particles from the water. An example of common sand filters in homes is refrigerator water filters and pre-filters of household water purifiers, which as sand filters are only able to absorb coarse particles and provide clear water for consumption.

Where are sand filters used?

• Swimming pool water
• Removes dyes dissolved in water
• Purification of return water from cooling tower
• Water purification of fish breeding ponds
• Purification of industrial and human wastewater
• Purification of surface water (river or well)
• Reverse osmosis (RO) pre-treatment water purification device
• Filtration for drinking and industrial uses (purification of urban and industrial water

Issues with no sand filtration (as pool surface is open)

If the pool water is not changed or filtered regularly, the water becomes stagnant and contaminated. The presence of foreign matter such as leaves, soil, dust and the growth and proliferation of microbes, microbial fungi and parasite eggs in the water cause diseases such as jaundice, enteric fever, dysentery, skin diseases, etc., especially in public pools. It should be seriously considered and addressed.

types of sand filters

Sand filters have differences in terms of body material, function, capacity, dimensions, number of silica layers and installation method.
In general, the sand filter has the following types.

Metal sand filter
Fiberglass sand filter (FRP)
Galvanized sand filter
Rapid sand filter under pressure

types of industrial sand filter in terms of material

One of the important criteria in the classification of sand filters is their body material. This material should be resistant to pressure, temperature, decay and other factors. In the following, the types of sand filters are discussed based on the material of the body.

metal sand filter

Sand filters with a metal body are one of the most resistant and stable types of sand filters against high pressure and heat. The extraordinary ability to withstand pressure and temperature along with wide applications in industrial environments is one of the prominent features of these filters. However, these filters perform poorly in contact with moisture and corrosive substances and are less durable in these conditions. It should be noted that the metal sand filters of the swimming pool are difficult to transport, install and maintain due to their high weight. Of course, metal sand filters have a higher filtration power than fiberglass sand filters. In general, the body resistance of fiberglass sand filters is lower than that of metal sand filters. For this reason, metal sand filter is mostly used in environments with high temperature.

fiberglass sand filter (FRP)

Fiberglass sand filters, which are also known as FRP sand filters, are used in many cases instead of galvanized and metal filters because they do not have the disadvantages of these filters, such as heavy weight and low resistance to moisture. Fiberglass materials have better tolerance against corrosive materials. Also, their weight is lighter, which makes them easier to move and install. However, it has less resistance to impact, pressure, and heat than metal types, and in case of damage to the body, it is usually not possible to repair them.

types of galvanized sand filter in terms of installation method

The galvanized sand filter is produced in 2 vertical and horizontal models, each of which is used according to the conditions of the respective space.

vertical galvanized sand filter

The vertical sand filter has a cylindrical tank and is installed on the base. Vertical sand filters are used for installation in environments such as engine houses that face a lack of space. According to the volume of water circulating in the purification system, the capacity and dimensions of the sand filter tank are different, but usually the vertical galvanized sand filter is smaller than the horizontal sand filter.

horizontal galvanized sand filter

The horizontal galvanised sand filter has a cylindrical tank and is installed in a horizontal position on a number of bases. Naturally, this sand filter takes up a lot of space due to the way it is placed on the floor. The Horizontal Galvanised Sand Filter is suitable for environments with limited ceiling height, but sufficient space on the engine room floor to install the filter.

types of sand filters in terms of performance

In the structure of sand filters, the amount of force that passes water through the nozzle determines their classification based on performance, which are divided into the following three groups.

rapid sand pressure filter

One of the most widely used types of water sand filters in industry and facilities, especially the physical filtration of water in swimming pools, is the pressurized sand filter. This sand filter is mostly used in industrial and domestic environments that require a higher speed for water purification. In this type of filter, the speed of water passing through the sand bed and nozzles is done using the pump and the upper part of the filter, and as a result, the output speed of water purification is done in a short period of time. The most used sand filter under pressure is in the filtration system of public and home pools.

Other types of sand filter are slow or slow sand filter and fast gravity sand filter, which are used for industrial applications such as urban water treatment, etc.

Carbon filters

Sand filters with activated carbon resin, which are used to remove free chlorine, color, taste, odor and organic matter in water, are called carbon filters.
The FRP and fiberglass sand filter is the most common type of filter for swimming pools, which provides an ideal filtration process with a suitable filtration speed. During the purification process, dirty pool water enters the filter through the inlet pipe. The pressure of the pool pump and the force of gravity directs the water down through the sand, and the fine sand removes any waste and debris from the pool water.
The use of sand filters in swimming pools, in addition to separating the above-mentioned suspended particles, also absorbs fats floating on the water to a large extent. At the bottom of the sand filters, there are nozzles with very small holes that suspended particles cannot pass through because of their small diameter, but the water passes through these nozzles and exits from the outlet pipe under the main sand tank.
The sand filter is selected based on the type of application required in terms of capacity, volume, working pressure, material and dimensions. Pressurized sand filters are made in different sizes and materials, the most common of which are vertical sand filters with a lens head. These filters are made of steel sheet (ST-37) or galvanized to the thickness specified in the ASME standard and for the upper and lower lenses using the DOUBLE-DISH method, after derusting from the inside with two layers of epoxy coating and The exterior is painted and used with one layer of stainless steel and two layers of special paint.
In addition, to improve the filtration quality and increase the life of pressurized filters, the filters can be sandblasted before painting. These types of filters are equipped with nozzles at the top that spread the water on the sand bed on the filter for better purification.
Also, at the bottom of these filters and under the last layer of silica inside, brass or plastic filters (brass or plastic nozzles) are installed to collect and pass water.
Inside the sand filters, there should be three different layers of silica with a uniformity factor of 1.35, with granularity under the types of special stones and purity above 95%.

• First grade silica with a diameter of 0.5 mm to 1.5 mm.
• Class II silica from 2mm to 3.5mm in diameter.
• Grade 3 silica from 4 mm to 8 mm in diameter.

All the silica poured into the sand filters should fill up to about 60% of the volume of the sand filter tank, and this has nothing to do with the filter capacity.

The total amount of sand required according to the grading of the sand

• Grade 3 sand (coarse) in the bottom of the filter in the amount of 20% of the total
• It sands grade 2 (medium) sand in the middle of the filter to the extent of 20% of the total
• Grade 1 sand (fine) in the upper part of the filter in the amount of 60% of the total.

The performance design of sand filters indicates that they should operate at a maximum flow rate of 10 GPM/ft2. Using the required power and the maximum pressure of the water flow, the required area can be calculated. The final point of the design is to ensure that the water flows properly in its bed and that no amount of liquid is diverted from the main flow path by sand and silica.

After some time, the water filter allows less water to pass through the accumulated dirt between the sands. These wastes remain in the filter and must be removed by washing. Now is the time to backwash the filter. This issue can be detected by increasing the pressure on the gauge.
When the filter absorbs a large amount of dirt, the pressure of the passing water drops and the water cannot flow freely through the sand filter. Backwashing runs water through the filter in reverse to remove dust trapped between the sand particles. After the back wash, the increase in water pressure in the pool is quite evident, and if a pressure gauge is installed on the filter, it can be seen that the pressure improves by more than 0.5 bar. This can be done through sand filter valves and pumps.
Automatic sand and carbon filters, which are usually made of FRP (wet fiberglass) and are not metal, are the best option for pool water purification. Note, however, that while these sand filters are highly resistant to moisture, they withstand less pressure than metal sand filters and are equipped with a multi-position valve that is much easier to use.

Design and calculation of sand filters

For the design and engineering of the sand filter, various factors must be considered, the most important of which is the linear velocity of the circulating water.
Normally, for swimming pool water, we consider a speed of 20 meters per hour for the linear speed of circulating water.
Also, the type of pool, public or private, is also influential in these calculations.
The purification process is considered between 3 and 8 hours in terms of time.
For example, consider a private pool with a volume of 100 cubic meters. In this case, all pool water must be filtered for at least 5 hours. With this account, it is necessary to filter 20 cubic meters per hour by sand filter. By considering these things and with the help of engineering tables, the dimensions of the required sand filter can be calculated.

Factors affecting sand filter performance

In physical filtration, many factors are effective in the correct functioning of sand filters. The most important factors to achieve maximum filtration efficiency are as follows:

Granulation size and shape of sand filter bed particles
The speed of water passing through the bed: the quality of purified water does not depend much on the speed of water passing through the bed, but the speed of water passing through the bed and the number of suspended particles in it are directly related to the operation time. Between two washes and pressure drop in the sand filter. The pressure drop in the sand filter indicates that the pores of the filter bed are blocked by suspended particles and absorbed sludge.
Filter washing method: depending on the type and dimensions of the filter, washing is done with water only or washing with water and air. In washing with water, the speed and pressure of the water should be such that it increases the bed volume by 15%, separated particles and trapped particles are removed from the bed. In large size filters, water alone is not able to disturb the sand filter bed, so air is used to stir the filter bed. For this reason, up to 60% of the total volume of the sand filter is filled with silica, not more.
Of course, it should be noted that the power of the pump should be selected so that the water pressure does not cause much disturbance to the silica bed, so that suddenly the silica or sand comes out of the filter and enters the pool bed.
back washing of sand filter (BACK WASH)
The inside of the sand filter tank is filled with silica or anthracite sand. Usually, to prevent clogging of the nozzles, a layer of coarse sand is poured on the nozzles, and then a layer of fine particles is poured on them. As a result of the water passing through the pores between the sand particles, the suspended particles in the water are stuck between the sands and the water almost free of suspended particles is obtained at the outlet of the sand filter. But the accumulation of suspended particles in the pores of the sand filter increases the pressure drop in the filter, and if this pressure drop exceeds a certain limit, the siliceous sands of the sand filter must be washed. (Back wash)

Backwashing in the sand filter is done simply by returning the pool water flow. In this way, by reversing the flow of water from the bottom to the top of the sand filter, the waste material stuck between the filter sands is transferred to the sewage.
To perform reverse washing, you must first turn off the pump and put the filter valve in the "Back Wash" position, and then turn the pump on again. Washing the pool sand filter usually takes 2-3 minutes. (This time depends on the type of silica used.) It is also possible to observe the water exit to the drain through the side glass on the multi-position valve.
When the water is clear, the backwash operation is complete.
After backwashing, turn off the pump and turn the valve to the "drain" position, then run the pump for 30-60 seconds to make sure all the dirty water in the backwash has gone down the drain. and does not enter the pool.
At this stage, stop the pump for the last time and put the valve on the filter.
Now turn on the pump and the filter will start purifying the pool water again.
A pressure gauge installed at the inlet and outlet indicates to the pool operator that the water passage in the filter is closing. If the gauge shows much more pressure at the inlet than at the outlet, the operator knows that there is too much debris in the sand. This means that it is time to "backwash" the filter.
To "backwash," the operator adjusts the valves to direct the water, closes the return pipe to the pool, and opens the outlet pipe to allow the water to enter the sewer system.

Buy a sand filter

The selection and purchase of sand filters depends on several factors such as the amount and flow rate of the desired water. You should choose a filter that is at least as large as the flow rate of your pump. Another factor is what kind of pool it is and how big is it? Is the pool private or public? And also how much filter it needs and how much time it takes to purify the water.
Considering all these factors is a really important step.
In order to choose and buy a sand filter easily, you must first determine the required capacity. On the website of the DamaTajhiz HVAC Inc, the technical information of dozens of sand filter models, from reputable brands with original warranty, has been presented, so that you, dear ones, can enjoy the good feeling of an optimal and smart purchase.

Also note that in the specialized HVAC group of Damatajhiz, all the sand filters are only sold in bulk. Therefore, if you want to wholesale any of these products, feel free to contact us.

Sand filter price

You can select and review all types of sand filters at the best price on the website of DamaTajhiz's HVAC Group. The price of the sand filter varies according to the variety of models and brands available in the market, it should be noted that the prices presented in the DamaTajhiz HAVC are up-to-date and the discounts desired by consumers have been included in these prices for wholesale purchase. So that these prices also include the guarantee of the best prices on the DamaTajhiz HVAC website.

Installment purchase of sand filters

For the convenience of you, dear customers, Dammatehez Group has provided the possibility of installment sales. You can refer to the installment purchase page to purchase the sand filter in installments.

When should sand filter sand be replaced?

According to engineers, silica used in sand filters should be usable for 5 to 10 years under normal conditions. While observations show that sometimes filters that have continued to work for more than 10 years without changing the sand, but they do not work as they should.
At the level of sand filters, the sand used is very coarse. This roughness is what makes the sand filter the suspended particles in the water. As these sands degrade over time, filter efficiency decreases, meaning your system has to work harder to achieve the same efficiency.
The findings show that in conventional silica after 5 years of continuous use, it can no longer fully absorb the pollution and the water does not become completely clear in the backwash. As a result, the filtration cycle is shortened and the need for backwashing increases, and for this type of silica, it is recommended to change the sand once a year (depending on the type of pool and its use).

Sand filters are used in the water purifier process for industrial or domestic use. They are responsible for separating suspended particles (usually up to 50 microns in diameter) from the circulating water by passing it through a bed of granulated sand and make the water clear and pure as a pre-treatment. Sand filters do not remove or absorb other chemicals in the water. Generally, these filters are used for swimming pool water, sewage treatment and home water treatment systems.

Dear user:

While thanking you for the trust you have in the technical opinions of temperature equipment sales experts, it should be noted that the determination and selection of the desired product brand based on history, brand strength, service and product price is ultimately determined by the buyer. But in the sand filter, most of the users and buyers choose and buy best-selling brands such as DamaTajhiz HVAC Group according to their quality, price and after-sales service.

If, after reading the above material, you have more questions in order to decide to buy the types of sand filters you need, you can get advice from the heating equipment and engine room sales experts after contacting the temperature equipment collection and extension numbers 107-108-121-122. and ask your questions.

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