Filters and Pumps
There are two main principles used to filter home pools.
- Sand filters and
- Cartridge filters
- Sand filters are pressure containers around one metre high and measured by their diameter.
- The filter media inside the filter container can be graded sand, crushed glass and a range other natural earth products.
- The most popular media selection appears to be the glass media which is easy to backwash.
- The water is forced through the media and the debris is collected inside the filter.
- The clean water then passes through to the chlorinator and returns to the pool.
- A pressure gauge on top of the filter alerts the owner when the filter is filled with collected pool rubbish.
- The filter system is then reversed by turning a valve on top of the filter and the waste is pumped away to a soak well or waste drain.
- This is called backwashing the filter.
- The pumps can deliver 300+ litres per minute so a considerable amount of water needs to be sent to waste.
- A 700 mm diameter filter may require four soak wells to hold the backwash.
Your pool designer should discuss the best place to backwash and incorporate soak wells into his design and quotation.
- Almost all of my clients elect to have modern compact cartridge filters.
- Cartridge filters don’t require soak wells and are not backwashed.
- Environmentalists approve of cartridge filters that don’t waste water or send dangerous chemicals into the ground.
- Smaller blocks of land often do not have the space to include four soak wells or even one larger soak well.
- The compact filters are also physically smaller and do not require as much area in the filtration plant area
- The cartridge filters also remove smaller particles than sand filters and hence provide a very clean sparkling pool.
- Investing in a larger cartridge filter reduces the workload of the owner and the filter may only require cleaning once a year.
- Think in terms of a bigger rubbish bin does not need to be cleaned as often as a small bin.
- Cartridge filters sizes are rated on the internal cartridge area of the collector.
- Most household pools of 40,000 litres require a 150 square foot area while a 400 square foot will handle up to 100,000 litre pool.
If I was planning a pool for me I would select a 400 square foot filter and reduce my pool maintenance. The simple work load consists of removing the internal collector and washing it with a garden hose. Of course you could engage a pool maintenance man to do this task for you if you wish.
Cyclones: A filter aid
- A cyclone or hydrospin is a pre-filter device fitted between the pool pump and the filter.
- Its function is to separate debris and small particles suspended in the water before they get to the filter.
- The shape of the cyclone forces the water to spin inside the device and centrifugal force pushes the debris to the bottom.
- The addition of a cyclone pre-filter greatly reduces the maintenance and cleaning of your pool filter system.
- The collected debris is simply decanted from a small draining valve in the base.
- Filtration cleaning is less frequent and the lifetime of a filter collector is greatly increased.
- The price of a cyclone is approximately $600.
This is a very large and varied subject.
Single speed pumps
- A single speed pump operates at the same speed all of the time apart from when the filter is dirty and hence back pressure has increased.
- Pump selection is based on water flow, circulation time and of course pool water volume.
- For a four hour turn over use the following simple formula:
- (Pool volume in litres divided by 4 hours) divided by 60 minutes = flow rate / minute
- For example (40000 divided by 4 hours) divided by 60 minutes = 166 litres/minute
- A good quality Zodiac flo pro 1.0hp pump provides approximately 300 litre/ minute
- Pools with water features may require a larger pump however a professional pool designer will prepare a specification to handle the pool requirements.
Multiple speed pumps
- Naturally clients wish to reduce their pool running costs.
- Multiple speed pumps can significantly reduce your electrical requirements and pool maintenance costs.
- Running the filter pump at lower speeds but over a longer period can save you up to 70% of your electrical costs.
- For example if the speed is halved, the flow output is halved, and the power consumption drops to one quarter.
- Pool control systems like Zodiacs Aqualink or Astral Viron range have artificial intelligence and can change the speed of the pump automatically for you.
- The lowest running cost system is not the cheapest pool system to purchase initially.