Circulation, Flow Rate and Turnover

Circulation Pumps

Swimming pool water is circulated around a circuit so that it can be filtered, heated and chemically treated before being returned to the pool.

Most circulation pumps work via centrifugal action. An outer casing encloses a rotating impeller that draws water in via vacuum suction. On the other side, the water is under pressure and gets forced along the pipework. The pumps need to be primed (i.e. flooded with water) at all times in order for this to happen.

Click through the slides to learn more about flow rate and turnover.

Have a go at this quick calculation.

Recommended Turnover Times

  • Diving Pools 4 – 8 Hours
  • Domestic Pools 4 – 8 Hours
  • 50m Olympic Pools 3 – 4 Hours
  • 25m General Use Pools 2.5 – 3 Hours
  • Leisure Pools Over 1.5m Deep 2 – 2.5 Hours
  • Leisure Pools 1 – 1.5m Deep 1 – 2 Hours
  • Leisure Pools 0.5 – 1m Deep 0.5 – 1.25 Hours
  • Leisure Pools Less Than 0.5m Deep 10 – 45 mins
  • Hydrotherapy Pools 0.5 – 1.5 Hours
  • Teaching Pools 0.5 – 1.5 Hours
  • Waterside Splash Pools 0.5 – 1 Hour
  • Interactive Water Features 20 mins
  • Domestic Spas 15 mins
  • Commercial Spas 6 mins
  • Leisure Water Bubble Pools 5 – 20 mins

Common Circulation Problems

Loss of prime describes a situation where the pump and pipework, which under normal conditions is flooded with water, is empty.

The impeller will be rotating, but will not be able to create the vacuum necessary to create the suction required to pull the water through the pipework.

The slides below will go through how to re-prime the system.

If air is drawn into the system it can create problems with visibility in the pool due to the tiny air bubbles that become entrained in the water returning to the pool from the treatment system.

Care must be taken when replacing the lids after having had the strainer vessel open as it can often be the case that the rubber O-ring that forms an airtight seal between the lid and the strainer vessel can be misaligned when replacing the lids and therefore wont form a good, airtight seal and will start to suck air into the circulation system when the circulation pumps are turned on.

This image has an empty alt attribute; its file name is 13092010057-1024x768.jpg
A pre-pump strainer basket removed from the strainer pot

If problems are encountered with pressure loss, there might be blockage. One of the most common places where blockages are encountered is in the skimmer baskets, especially with outdoor pools due to leaves etc. There might also be a build up of material in the pre-pump strainer basket if it hasn’t been maintained and cleaned out regularly.

Unfortunately, the design and construction of swimming pools and associated treatment systems is not tightly regulated and there are many examples of systems that are poorly designed. Examples of problems include:

  • Incorrectly sized pipework
  • Incorrect pipework material
  • A ‘mish-mash’ of different pipework materials
  • Too many right angled bends
  • No valves fitted where there should be valves
  • No pressure gauges fitted to filters
  • No air bleed system fitted to filters
  • No flow rate meter fitted to system

It’s not just contractors who are at fault – clients also need to take responsibility for not properly specifying a contract for the work, or selecting a contractor based solely on price, with inadequate consideration given to competence and quality.