What Size Pool Pump Do I Need?

by Francis Lowe⁽¹⁴⁾
http://www.poolwarehouseuk.com/

The pump is the heart of your pool water system, circulating water so that it can be filtered, heated, cleaned and chemically treated. Without a pump the pool will quickly become 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. Consequently, it is worth doing the correct sizing exercise regardless.

The factors that need to be considered can be summed up as "flow rate" and "head".

The amount of water moved in any given period of time is known as the flow rate. This is usually worked out in gallons per minute. To work out your required flow rate you first need to work out your pool volume. All measurements should be taken in feet. To find the average depth of your pool, take an average of the deepest and shallowest points.

Pool Volumes.

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. It is recommended that this is every 6 hours, but can be varied depending on the bather load. If we assume turnover required is six hours then the flow rate in hours is the volume divided by 6. 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 very difficult to do, and is only theoretically possible on new builds. There are very many variables and too many unknowns. To be completely accurate you need to know the exact length of all pipe work, exact location of joints, what they are made of, who by, 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 would be reasonably accurate for most pools where the pump is sited about 30 feet from the pool and is on the same level. Take this 10m figure as a starting point and adjust upwards or downwards if there are any unusual features, such as the pump on a lower level.

Once we have calculated the required flow rate, and estimated the head, then we need to look at the pump curve charts provided by the pump supplier.

All pump curve charts show the flow along the horizontal axis, measured against the head along the vertical axis. At the point where your two readings cross, go to the next pump curve up. That is then the pump you require.

Francis Lowe is a leading expert in swimming pool maintenance with a huge wealth of experience developed from 40 years in the industry.

To see a full range of pool equipment, including swimming pool pumps and pool pumps please see the website of specialist supplier poolwarehouseuk.com

Article submitted Saturday, January 28, 2012 & read 43 times.

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