All swimming pools whether residential or commercial, just used for leisure, fun, or serious competitive swimming, need the pool water to be circulated, filtered, heated and chemically treated to keep it clean, safe and hygienic. Without a good filtration system, water can become dirty, unsanitary and even hazardous. As far as filtration goes, in the UK there are two types of pool filters that are available, sand filters and cartridge filters, and both have pros and cons, advantages and disadvantages. The type of filter you choose for your swimming pool will affect factors like how it’s maintained, how often the filter needs to be cleaned and how effective your pool filtration is.

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Sand Filters

High rate sand filters are the most common and affordable filters available for in-ground pools in the UK market. They’re also the oldest type of filters in circulation and because they’ve been around the longest, homeowners tend to be familiar with the technology.

 

Though sand filters have their downsides, they have a simple design, relatively straightforward to install and service plus parts are commonly available to homeowners. For these reasons and others, they’re naturally easy to maintain.

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How sand filters work:

Sand filters work by using a bed of sand to trap particles and other contaminants, which are then removed from the water through a process called backwashing. 

• Water from the swimming pool is pumped into the filter vessel using a pool circulation pump, the pump has an inbuilt strainer basket that stops large debris to go into the filter.

• The water flows through a layer of sand, which acts as a natural filter to trap contaminants and other unwanted particles.

• The filtered water is then circulated through a pool heater to heat the water, followed by addition of pool chemicals and then returned to the swimming pool through the swimming pool return inlets.

• Over time, the sand in the filter becomes clogged with contaminants, which can reduce the efficiency of the filter.

• To clean the filter, the flow of water is reversed through the filter using a process called backwashing. This helps to remove the trapped contaminants from the sand, allowing the filter to function more effectively.

• Sand filters are an effective and low-maintenance way to keep swimming pool water clean and clear. They are typically easy to operate and require minimal attention, making them a popular choice.

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Advantages of sand filters:  

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• Easy to use

• Low maintenance

• Easy to backwash

• Relatively low maintenance price

• Sand is easy to change

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Disadvantages of sand filters: 

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• Cannot remove very small suspended contaminants

• Regular backwashing is required

• Less effective than cartridge filters

 

Cartridge Filters

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Although very popular in the US, Australian, and even the European swimming pool market, cartridge filters have struggled to get popular in the traditionally conservative UK swimming pool industry. Cartridge filters work by using a paper or fabric cartridge to filter out particles and other contaminants, which can be removed and cleaned or replaced as needed.

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How cartridge filters work:

Cartridge filters work by using a paper or fabric cartridge to filter out particles and other contaminants, which can be removed and cleaned or replaced as needed. 

• Water from the swimming pool is pumped into the filter body using a pool circulation pump, the pump has an inbuilt strainer basket that stops large debris to go into the filter.

• The water flows through the cartridge, which is made of a porous material that traps contaminants and other unwanted particles.​

• The filtered water is then circulated through a pool heater to heat the water, followed by addition of pool chemicals and then returned to the swimming pool through the swimming pool return inlets.

• Over time, the cartridge becomes clogged with contaminants, which can reduce the efficiency of the filter.

• To clean the filter, the cartridge is removed from the filter and cleaned or replaced with a new one. This helps to remove the trapped contaminants, allowing the filter to function more effectively.

• Cartridge filters are an effective and low-maintenance way to keep swimming pool water clean and clear. They are typically easy to operate and require minimal attention, making them a popular choice.

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Advantages of cartridge filters:  

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• Easy to install in compact places

• Less pipework needed in plant room

• No need to backwash

• Can remove very small suspended contaminants

• Relatively low purchase price

• Cartridge is easy to change

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Disadvantages of cartridge filters: 

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• Require more frequent cleaning or replacement than sand filters

• Expensive to operate, as the cartridges can be more costly to replace than the sand

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Swimming Pool Circulation Systems

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Swimming pool circulation is achieved through the use of a pool circulation pump and filter system. The water is drawn from the pool through the skimmer, overflow channel, or balance tank along with main drains, and then pushed through the pool filter and heater  before being returned back to the pool through the return inlets. Proper circulation is important for several reasons:

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• Filtration: As water is circulated through the filter, it removes dirt, debris, and other contaminants, helping to keep the water clean and clear.

• Chemical Distribution: By circulating the water, chemicals such as chlorine are more evenly distributed throughout the pool, ensuring that they are able to effectively disinfect the water.

• Temperature: Proper circulation helps to evenly distribute the heat throughout the pool, keeping the water temperature consistent and comfortable.

• Water Movement: Circulation promotes water movement, which can help to prevent stagnant areas and reduce the potential for algae growth.

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There are several types of outdoor pool circulation systems that we design and install, each has its own merits so it certainly helps to ascertain the suitability to a particular project as every pool is unique and the most important thing to take into consideration is the client's needs. The main difference, apart from placement of pool shell fittings,  is the construction of the shell according to the flow of the water. With proper design and construction, a pool will be much easier to maintain and it will offer you joy and relaxation for many years to come.