What Are Backwashing Filters and How Do They Work?
Backwashing is the process of filtering and purifying water, by forcing it back through the filter medium. This process allows the filtering media to be cleaned, maintained, and reused for a longer time. Automatic Backwash Filters are the most popular types of these filters used in industries. We will discuss more of that in the coming segments.
Backwashing filters are very common in households and industrial applications to filter water, liquid fuels, industrial fluids, and other low-viscosity fluids.
The basic processes involved in backwashing are separation, adsorption, and the addition of extra media that can be sacrificed during the backwashing. Generally, filter beds start accumulating dirt and contaminants and become unusable or get quality problems with time. With backwashing though, the filter bed is constantly cleaned by directing the flow of water or a combination of air and water to the bed directly. This cleans the filter and maintains its quality.
There are several steps involved in backwashing your filters.
- The filter is removed and the water is drained out until it is exactly above the filter bed.
- Compressed air is sent up the filter media, breaking the structure of the granules and forcing the accumulated particles into suspension.
- Now, backwash freshwater is sent through the filter bed and this pushes the suspended particles into the backwash troughs.
- This process continues until the turbidity has reduced to an appropriate value.
- The number of backwash cycles needed depends on how contaminated the filter bed is.
Backwashing filters requirements
There are not a lot of complicated requirements for a backwashing filter. You have to make sure the below processes and parts are in place.
- Backwashing filters have to be placed on a level surface for them to work effectively
- A tank that can collect the contaminants
- Adequate and continuous power supply
- Drainage to flush out the used water
- Well-ventilated and shaded area to place the filter in
When some models of the backwash filters are cleaning themselves, they will not be able to provide water to your operations. If you run a unit where a 24X7 water supply is necessary, then it makes sense to invest in more than one backwash filter. This way, when one is getting cleaned, the other one can still work on supplying water. Instead, you can also consider investing in models that can clean themselves while still supplying water. These may be slightly more expensive but are worth the investment.
The quality of filtration and backwashing depends on the type of filter media used, the size of the filter, and the type of fluids that are filtered. Irregularly sized contaminants are going to bring down the efficiency of the filter.
Similarly, larger filters have a smaller backwashing rate than smaller filters. Make your choice smartly.
What are the Types of Backwash Filters?
Based on how the process is designed to work, there are two basic kinds of backwash filters
- Manual backwash filters – Manual backwash filters have to be manually set for backwashing periodically by those handling them. It is important to check for differential pressure changes and other abnormalities from time to time and then opt for backwashing.
- Automatic backwash filters – With Automatic Backwash Filters, this process is seamless and automatic. The filter identifies problems in the quality of filtered water and schedules backwashing, without manual intervention.
Depending on the type of filter media used, these are the different kinds of backwashing filters identified.
- Micro-contaminant backwashing filters – These are used when the contaminants are less than 0.2 microns in size. Such micro-contaminants are not easy to remove from the liquid. Such filters make use of filter media like Granulated Activated Carbon (GAC), Manganese Green Sand, Brim, or Pyrolox to remove these contaminants. Such minute contaminants are not visible to the naked eye and are mostly in the form of dissolved minerals or ions.
- Sediment backwashing filters – These are used in removing slightly larger sediments from the liquid to be filtered. These filters commonly use filter media like FilterAG which is a type of silica mineral, anthracite, Zeolite, and calcite.
Are Backwashing Filters the same as Self-cleaning Filters?
A self-cleaning filter, as the name specifies, cleans itself periodically, to improve the life of the filter medium and brings down maintenance instances. Backwashing filters are a type of self-cleaning filter. The latter, however, includes other types like direct flushing filters and suction scanning filters, along with backwashing filters.
What are the Benefits of Backwash Filters?
- Backwashing filters are self-rejuvenating. It means that they keep upgrading their performance and remain new and effective for a longer time.
- Such filters keep removing containments from their surfaces often. As a result, the chances of infections in the treated water or liquid are very low.
- The backwashing process reactivates the filter media. As a result, the filter’s efficiency keeps improving with time.
- Lowered chances of filter failing and lowered chances of you having to stall operations due to lack of clean fluids.
- Automatic Backwash Filters work regularly even while supplying clean water to your unit.
- Filters are easy and cheaper to maintain. These filters are a very smart investment in operations where the filtration process is a critical part of the operations.
What are the Disadvantages of the Backwash Filter System?
- Cost – Such filters are more expensive than regular filters. However, with time, the money you save on maintenance and repairs will pay for this excess cost.
- Maintenance – Backwash filters also have to be periodically maintained to ensure the backwash process happens effectively. Else, the filter media is going to get contaminated with time.
- Replacing filters – Just because you have invested in backwash filters doesn’t mean these are permanent installations. These also have to be replaced with use. Problems like tattered filter elements, damaged cartridge, fully exhausted filter media, and abnormally high pressure readings consistently can all mean that your filter has reached its end-life and needs to be replaced.
What is an Automatic Backwashing Filter?
One of the most popular types of backwashing filters is the Automatic Backwash Filters. As the name specifies, these filters automatically take care of the backwashing and filtering processes. Such automated filters are largely used in chemical industries, power industries, and oil industries.
How Does an Automatic Backwashing Filter Work?
The basic parts of any Automatic Backwash Filter are:
- Inlet and outlet ports
- Filter media
- Drain valve
- A control system
- Pneumatic actuator and differential meter
- Main external housing
Some of the common applications of these filters are:
- Seawater and other saltwater sources desalination
- Cooling water filtration
- Recycling water filtration
- Water reinjection in mines and oil fields
- Water filtration for reverse osmosis
- Filtration of spray nozzle water
How does a backwash filter clean itself automatically?
The process that happens inside an Automatic Backwash Filter is simple and straightforward.
The fluid is sent inside through the inlet valve and passes through the multi-layered filter media. Contaminants are trapped inside the media and clean fluid is sent out through the outlet valve. As this process happens, the actuator and meter keep reading the pressure levels inside and outside the filter screen (media). When the filter media is accumulated with the contaminants beyond a specified value, there is a differential pressure noted.
When this differential pressure is noted, the filter starts its backwashing process to flush out the contaminants from the medium. The process is simple but works great every time.
In an automated backwash filter, you do not have to monitor the pressure differential every time. The high-end control panels take over the job and initiate backwashing automatically.
Once the backwash cycle is activated, the drain valve opens. Now, fresh water is forcefully flushed through the media, and the contaminants and other pollutants are pushed out. These pollutants mix with the water and are sent out through the drain valve.
Depending on how the backwash process is designed, it can run for a specified period of time. After this, the drain valve closes automatically and the regular filtration process starts back.
In which systems do the automatic backwash filters work?
Automatic backwash filters can be used in a variety of industrial systems including the following.
- Water treatment plants
- Oil refineries
- Power generating plants
- Sewage treatment plants
- Irrigation systems
- Mining industries
- Gas sectors
- Nuclear plants
- Petrochemical industries
- Snow production plants
- Paper production plants
Advantages of Automatic Backwash Filters
- Self-cleaning – One of the main advantages of automatic backwash filters is their ability to self-clean. Imagine having multiple huge filters installed in your operations unit. Manually checking the levels and initiating cleaning is going to be a full-time job that needs multiple hands. You can install these automatic filters and forget about them. Manual labor can instead be utilized elsewhere, improving productivity.
- Periodically maintains filters – Filters used in industries can be really expensive. Even the smallest of repairs can cost millions. By periodically maintaining the filters, you can avoid such money spent on maintenance. Periodical cleaning also helps improve the lifespan of the filters.
- Easy to use – Such filters can be installed and forgotten as they are super easy to use and maintain. Your employees can depend on the automatic backwashing ability and invest their time and efforts in other productive tasks.
- Minimal liquid loss – Automatic backwashing uses minimal liquid when compared to manual cleaning of the filters. This helps your unit save electricity and resources with time.
- Always maintains optimal levels – Abnormal changes in the filter are what lead to damages to the unit over time. Automated processes like these constantly check and maintain optimal levels, thereby improving efficiency.
What is the difference between Manual and Automatic Backwash Filter?
In manual backwash filters, the backwashing processes need to be manually set up. If you forget to set up the process, the filter will keep performing inefficiently and the filtered fluids would start deteriorating in quality.
With automatic backwash filters, the backwashing instruction is provided by the filter itself, based on the differential pressure it notices. The minute the filter medium exceeds the recommended contamination levels, the backwashing process is automated.
When should you replace Backwash Filters?
Here are situations where you may have to change the backwash filters.
- Expired lifespan – All backwash filters come with recommended lifespan. Irrespective of whether the filter works or not, it has to be discarded after it crosses the recommended time frame.
- Damaged cartridges – It is normal for the cartridges to get dirty with regular use. In such cases, you can clean the cartridge and start using the filter again. However, if the cartridge is damaged, you will not be able to use the filter and may need to replace the filters.
- Pressure differential even after backwashing – The pressure differential values should usually normalize after backwashing. If that doesn’t happen, it means the filters have become very old beyond backwashing help and have to be replaced.
- Torn or damaged filter element – The filter element is the central, vital portion of the filter where the actual filtration process takes place. If this is torn or damaged, then no amount of backwashing is going to help. You need to change the filters.
Comparing backwash and normal filters
Both backwash and normal filters do the same job – they filter water or other fluids and remove contaminants and sediments. The difference lies in how these filters have to be cleaned and maintained.
Normal filters have to be manually checked for quality discrepancies and cleaned once in a while to maintain their quality. If you are slack or careless, then chances are your filter won’t last long and is going to become a financial burden to the company over time.
Backwash filters have the ability to check for quality discrepancies automatically and can activate the backwash mode. With backwashing, the filter media is force-cleaned so contaminants and sediments are sent out through a drain valve. It is easier to maintain backwash filters and these have an increased lifespan too, especially the automatic backwash filters.
Buying filters is definitely a considerable investment for your industry. Since the investment is huge, you need to do the research right to pick the right model with the right filter medium. Automatic backwash filters are cost-worthy and more effective than normal filters.
Consider factors like purpose, how many hours these filters will have to run, the criticality of the filters for your process, and what type of fluids will be filtered.
Based on this, you can choose the right filter size and filter medium to improve the efficiency of these filters. Self-cleaning filters are the future of the filtration industry and these can indirectly quicken your production speed and improve profits too.
Multitex offers customized filtration solutions to companies across niche industries. If you are looking to invest in a new filter or change the existing one, get in touch with us to know what kind of filters work best for you.
We have hands-on experience in delivering consistent solutions for five decades and run manufacturing and engineering facilities that are accredited by international organizations.