How To Work Out The Size Of Pump Required
The heart of any swimming pool is the circulation pump, which allows the water to be filtered, heated, vacuumed and chemically treated. A pool without a pump is useless.Therefore, when first installing or replacing your pump it is extremely important that it is the correct size for your pool. It is vital that the correct size pump is installed. Problems can occur if it is too small i.e not enough circulation and filtration, resulting in cloudy water, or if too big can cause a strain through increased pressure on the pipe work and or filter body.The aim is to install a pump which will filter your entire pool water volume every 6 to 8 hours, depending on the swimming load.
If replacing an existing pump, it is tempting to just install the same size as the original. For this to work it depends on the original being correct in the first place. As such it is therefore worth going through the correct sizing procedure anyway.
The factors that need to be considered can be summed up as "flow rate" and "head".
The flow rate is the amount of water moved in a given time, usually expressed in gallons per minute. Before you can find the flow rate, you need to know the volume of your pool. For these formulae, take the measurements in feet. To find the average depth of your pool, take an average of the deepest and shallowest points.
Pool Water Volumes.ed or Oval Pools : Avg Width x Avg Length x Avg Depth x 6.25 = Gallons
If replacing an existing pump, it is tempting to just install the same size as the original. For this to work it depends on the original being correct in the first place. As such it is therefore worth going through the correct sizing procedure anyway.
The factors that need to be considered can be summed up as "flow rate" and "head".
The flow rate is the amount of water moved in a given time, usually expressed in gallons per minute. Before you can find the flow rate, you need to know the volume of your pool. For these formulae, take the measurements in feet. To find the average depth of your pool, take an average of the deepest and shallowest points.
Pool Water Volumes.ed or Oval Pools : Avg Width x Avg Length x Avg Depth x 6.25 = Gallons
Rectangular Pool : Length x Width x Average Depth x 6.25 = Gallons
Round Pool : Radius x Radius x Average Depth x 20 = Gallons
Shaped or Oval Pools : Avg Width x Avg Length x Avg Depth x 6.25 = Gallons
When you have worked out the pool volume, set a turnover time. Ideally this will be about every 6 hours, but can vary according to bather load. To work out the flow rate, divide the volume by the turnover in hours. This figure must then be divided by 60 to get gallons per minute.
Having worked out the flow rate that we need, we then have to look at the head loss, which is a measure of the resistance, for example friction in pipe work, that the water will encounter on its journey around the circulation system.
This is an extremely difficult thing to establish accurately. There are simply too many unknowns and too many variables. For example, to be 100% accurate you would need to know exactly how many feet of pipe you have, exactly how many joints, where they are, who manufactured them, what they are made of, etc,etc.
In practice it is only feasible to take a best guess. For most domestic pools, it is accepted that the average figure for "head" is 10 metres or 33 feet. This will usually be reasonably accurate for most pools where the pump is situated no more than 30 feet from the pool, and on the same level. Use this as a starting point and adjust upwards if your installation is further away, has lots of bends, or is at a lower level.
Round Pool : Radius x Radius x Average Depth x 20 = Gallons
Shaped or Oval Pools : Avg Width x Avg Length x Avg Depth x 6.25 = Gallons
When you have worked out the pool volume, set a turnover time. Ideally this will be about every 6 hours, but can vary according to bather load. To work out the flow rate, divide the volume by the turnover in hours. This figure must then be divided by 60 to get gallons per minute.
Having worked out the flow rate that we need, we then have to look at the head loss, which is a measure of the resistance, for example friction in pipe work, that the water will encounter on its journey around the circulation system.
This is an extremely difficult thing to establish accurately. There are simply too many unknowns and too many variables. For example, to be 100% accurate you would need to know exactly how many feet of pipe you have, exactly how many joints, where they are, who manufactured them, what they are made of, etc,etc.
In practice it is only feasible to take a best guess. For most domestic pools, it is accepted that the average figure for "head" is 10 metres or 33 feet. This will usually be reasonably accurate for most pools where the pump is situated no more than 30 feet from the pool, and on the same level. Use this as a starting point and adjust upwards if your installation is further away, has lots of bends, or is at a lower level.
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