Choosing the right filter for your pool is not always a simple procedure. Before proceeding with the purchase, it is better to know every detail of the system to buy the best model; afterwards, you can go to various pool supply centers and buy the suitable piece that guarantees perfectly clean water.
Steps
Step 1. Calculate the surface and volume of water that the pool can hold
Pools come in various shapes, although the most common are two: rectangular and circular. Based on the one you have, calculate the capacity correctly using the appropriate mathematical formula.
- For rectangular pools, the procedure is quite simple: multiply the length by the length. Area = Length x Width.
- If you have a round pool, such as a whirlpool or a small children's model, you need to find the radius of the circumference, raise it to the second power and multiply the result by 3, 14. Area = r2 x 3, 14.
- You can take the measurements yourself and calculate the surface, but if you just bought the pool, the data should have been provided to you at the time of purchase.
Step 2. Find the maximum volume
The next step is to calculate the capacity of the pool to find out how much water can be filtered per minute. This data is defined as "flow rate" and varies according to the type of pool in your possession; take this information into consideration to maximize the function of the filter itself.
- To find the flow rate of the pool, take its maximum capacity (a value that is generally communicated to you at purchase) and divide it by 360; by doing so, you can know how many liters of water pass through the filter in one minute.
- To ensure maximum efficiency, it is better to choose a model that is slightly oversized compared to the needs of the pool.
- If the flow velocity is too high for the filter, which is forced to withstand an excessive operating pressure, you can increase the diameter of the system pipes (all or only some), consequently reducing the pressure itself.
- All filters are calibrated at a minimum and maximum flow rate; that of the pump must be within this range. Too weak or too strong flow prevents the filter from working properly. Make sure the model you choose is able to clean the amount of water in the pool.
Step 3. Determine the recycling rate
This means you need to know how long it takes the system to filter all the water present. Most municipal regulations regarding water safety and hygiene require a speed equal to one or two complete cycles in 24 hours.
- The minimum speed corresponds to a complete recycling in 12 hours, while modern swimming pools guarantee complete filtration every 8-10 hours.
- If the pool is used for commercial, semi-commercial or very busy purposes, you must choose a filter that cleans all the water at least 4 times in 24 hours.
Step 4. Choose the correct model
This depends on the size of the pool; to maintain good water quality you have to start the pump every day, so that all the liquid is filtered. Each filter has a certain flow and recycling rate.
For example: consider a circular above ground pool, with a diameter of 7 m and which contains about 51,000 liters; in this case, you need a filter with a recycling rate of 69,000 liters in 10 hours
Step 5. Take into account the resistance of the water which could affect the recycling rate
The faster the water moves in the pump, the greater the resistance it exerts.
- Choose a filter that can treat all the water in at least 10 hours. When it comes to these components, it's worth overdoing it a bit; larger filters maintain good water quality.
- Remember that the faster the water flows into the water system, the greater its resistance; this means that a slower pump (such as a low-speed, two-speed one) guarantees an increase in flow per unit of power compared to a high-speed model. Note that most two-ratio pumps set at low speed do not meet the minimum flow requirements for the filter to function properly.
Step 6. Take all of this pool information into consideration to determine the correct filter size
Using a simple equation you shouldn't run into any problems. Before proceeding, make sure you have found the volume (in liters) of the pool and have decided on a reasonable recycling rate. The equation you should use is:
- Pool capacity expressed in liters divided by the desired recycling rate.
- With this calculation you get the minimum flow value you need expressed in liters per hour.
- Divide it by 60 to define the flow in liters per minute.
- Find a pump that satisfies the figure you just calculated.
Advice
- Call the pump manufacturer to help you calculate the approximate head of your plumbing installation. You need this data to find the flow (liters per minute) of the pump itself.
- A list of the most common pool sizes, their filters and their speed could help you in the selection process.
- Two-speed pumps are effective in reaching minimum replacement values while consuming as little electricity as possible; try using two filters to maximize efficiency.
- The filter you choose should have a 15-20% higher flow rate than the pump, according to your calculations.
- Most old filters are made to withstand a maximum pressure of 2 bar; this value instead represents the operating pressure of the new models which can withstand up to 3.5 bar.
- If the pool has an abnormal shape, you can look for an online calculator to help you define its capacity.
