Sand Filter

Sand filters are used to filtrate water by removing water particles and, producing clean water for pools, and other uses. The following content provides key details on sand filter characteristics, sizing, models, and optimal pricing for wholesale purchases.

Sand Filter Review, Selection, and Pricing

Sand filters are tanks made of galvanized steel, stainless steel, and fiberglass which are made in sphere and square shapes under atmospheric pressure.

They remove suspended particles in the water such as mud, paint residue, etc. An example of common sand filters in homes are refrigerator water filters and household water purifier pre-filters. However, these types of sand filters are only able to absorb coarse particles and provide clean water for consumption.

Types of Sand Filters

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

Types of Sand Filters 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:

Steel Sand Filter

Sand filters with a steel 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 steel sand filters of the swimming pool are difficult to transport, install, and maintain due to their high weight. However, most steel sand filters have a higher filtration power than fiberglass sand filters.

Galvanized Steel Sand Filters

The galvanized sand filters are produced in vertical and horizontal models, each of which is used according to the conditions of the site.

Vertical Galvanized Steel Sand Filter

The vertical sand filters have a cylindrical tank (sphere) and are installed on a base or holder. Vertical sand filters are used for installation in environments face a lack of space such as engine rooms.

According to the volume of water circulating in the filtration system, the capacity and dimensions of the sand filter tank are different, but usually the vertical galvanized sand filters are smaller than the horizontal sand filters.

Horizontal Galvanized Steel Sand Filter

The horizontal galvanized steel sand filters are also spherical but the difference is that they are mounted horizontally.

Naturally, these sand filters take up a lot of space due to the way they are positioned on the floor. The Horizontal Galvanised Sand Filters are suitable for environments with limited ceiling height, but sufficient space on the engine room floor.

Fiberglass Sand Filter (FRP)

Fiberglass sand filters, which are also known as FRP sand filters, are used in many places where steel sand filters cannot stand. Because steel sand filters are much heavier and not that resistant to moisture.

Fiberglass has a better resistance against corrosive materials and they are lighter than steel sand filters, which makes them easier to transport and install. However, FRP sand filters have downsides too, such as less resistance to impact, pressure, and heat, and their body is not repairable.

Note: The heat resistance of fiberglass sand filters is lower than steel sand filters. For this reason, a steel sand filter is mostly used in environments with high temperatures.

Types of Sand Filters in Terms of Waterflow

In the structure of sand filters, the amount of force (pump or gravity) and the flow of water through the nozzle are divided into the following three groups.

Rapid Sand Filter (Gravity)

Rapid sand filters AKA gravity sand filters are tanks with underlying filtering sand at the bottom. They work by gravity force as the incoming pipe is located at the top of the filter where dirty water comes in and after passing through layers of filtration sand goes down to the bottom and comes out as debris-free water.

Pressure Sand Filter

One of the most widely used types of water sand filters in industry and facilities, especially for 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 filtration.

In pressure or gravity sand filters, the speed of water passing through the sand bed and nozzles is done using a pump. As a result water filtration is usually done much faster. Pressure sand filters are mostly used in the filtration system of public and private pools.

Upward Flow Sand Filters

The upward-flow sand filter is an elaborate structure, that washes itself as well as provides the water with high-quality filtration. It is discharging through a pipe and the water spreads out across very much sand in the filter.

The water then moves up through the sand, and the sediments in the liquid separate from it and sink to the bottom. Effused clean waters drain at the top of the filter, through an outlet. This always means that the filter goes through the cleaning cycle constantly to provide clean water in the case where the pressure is constant.

Slow Sand Filters

Slow sand filters simply entail water passing through sand beds without any pressure thereby depending on natural biological actions within the water. Most slow sand filter cleanings involve the use of a mechanical scraper that is taken into the dried sand bed whereas others use wet harrowing.

What is a Sand and Carbon Filter?

Sand filters with activated carbon resin, which are used to remove chlorine, color, taste, odor, and organic matter in water, are called sand and carbon filters.

Sand Filter Applications

Sand filters offer a vast array of uses such as:

• Swimming pool water
• Removes dyes dissolved in water
• Purification of return water from the 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)
  
  

Swimming Pool Sand Filters

The FRP sand filter is the most common type of filter for swimming pools, which provides an ideal filtration process with a suitable speed.

During the purification process, dirty water enters the filter through the inlet pipe. The pressure of the pool pump directs the water down through the sand, and the fine sand removes any waste and debris from the pool water.

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.

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.

Why Every Swimming Pool Needs Sand Filters

If the pool water is not changed or filtered regularly, the water becomes stagnant and contaminated by removing water particles and sediments from the water making it ready to be used in pools and other places.

The presence of leaves, soil, and 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. Which should be seriously considered and addressed.

Types of Sand Grades in Sand Filters

There are 3 types of sand grades:

1. Grade 3 sand (coarse) in the bottom of the filter in the amount of 20% of the total.
2. It sands grade 2 (medium) sand in the middle of the filter to the extent of 20% of the total.
3. 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 backwash, 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 steel, 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 steel sand filters and are equipped with a multi-position valve that is much easier to use.

Filtration Capacity of Sand Filters

For the design and engineering of a sand filter with enough capacity, some values must be estimated:

1. 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.
   
   
2. The type of pool, public or private, is influential in these calculations. The purification process is considered between 3 and 8 hours.
   
   

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, so 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:

Sand grade and Shape of the Sand Filter

As we mentioned this concept before, the sand grade has a large effect on how the sand filter will work and for how long.

The Water Flow Speed in the Sand Filter

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.

Sand Filter Washing Method

Depending on the type and dimensions of the sand 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 filter volume by 15%, and separated particles and trapped particles are removed from the filter.

In large sand filters, water is not able to disturb the sand filter on its own, so air is used to stir the filter. For this reason, up to 60% of the total volume of the sand filter is filled with silica and not more.

Note: 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.

What is the Sand Filter Backwashing

Sand filter tanks are 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 placed on them.

As the water passes through the pores between the sand, the suspended particles in the water are stuck between the sands, and the water almost free of particles is obtained at the outlet of the sand filter.

However 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 which is called backwashing.

How to Backwash a Sand Filter

Backwashing in the sand filter is done simply by reversing the pool water back into the sand filter. In this way, the water goes from the bottom to the top, washing all the debris stuck in the sand and directing it into the sewage. To perform reverse washing:

1. Turn off the pump
2. Put the sand filter valve to "Backwash Mode"
3. Turn on the pump
4. Wait for at least 3 minutes until the water is clear
5. Turn off the pump
6. Put the valve to "Drain Mode"
7. Turn on the pump
8. Wait for 30-60 seconds to drain the dirty water
9. Turn off the pump
10. Put the valve to "Filter Mode"
11. Turn on the pump as the backwashing is not completed
    
    

Note:

Washing the pool sand filter usually takes 2-3 minutes. But 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 is it Time to Backwash a Sand Filter?

A pressure gauge is usually installed at the inlet and outlet of the filter, indicating higher pressures if the water flow is slowed down or blocked. If/When that happens it is time to backwash the sand filter as there is too much debris in the sand.

When is it Time to Change the Sand in a Sand Filter?

According to engineers, silica used in sand filters should be usable for 5 to 10 years under normal conditions. Observations show that sometimes filters continued to work for more than 10 years of not changing the sand, but not perfectly.

At the level of sand filters, the sand used is very coarse. This roughness is what makes the sand to filter the 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.

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 granulated sand and making the water clear and pure as a pre-treatment.

Note: Sand filters do not remove or absorb other chemicals in the water. Generally, these filters are used for swimming pool water, sewage, and home water treatment systems.

Why DamaTajhiz Sand Filters?

All sand filters presented on DamaTajhiz HVAC 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 de-rusting 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.

How to Choose the Right Sand Filter

The sand filter is selected based on the type of application required in terms of capacity, volume, working pressure, material, and dimensions. Pressure sand filters are made in different sizes and materials, the most common of which are vertical ones.

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 the type of swimming pool (Private or Public) and how big it is. also how much filter it needs and how much time it takes to purify the water.

In order to choose and buy a sand filter easily, you must first determine the required capacity of the sand filter.

On this website, technical information of dozens of sand filters, from known brands with original guarantees, has been presented, so that you can enjoy the good feeling of an optimal and smart purchase.

Sand Filter Price

You can browse through all types of sand filters at the best price on DamaTajhiz HVAC. 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 are already included.

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 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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