How A Pool Works

Every pool owner wants to achieve crystal clear and sparkling water. This page explains, in simple terms, how a pool works and what you need to do to obtain and keep that crystal clear water.

The principle, for hundreds of years, has been cleaning our drinking water by straining it through sand. The same principle is used in pools only we force the water through the sand or, now more commonly used, glass filter media.

The pool or spa is a closed water system which means the water stays within the pool tank and associated pipe work. Therefore it is not subject to outside forces other than when you top up with fresh water or with rainfall. The pool water is simply sucked from the pool tank by the pool circulation pump via the skimmer (the top water inlet). The circulation pump is responsible for the circulation of the pool water through the system. The pump should be correctly sized for the pool/filter dimensions.

The first part of the pump is a coarse strainer basket. The purpose of the coarse strainer is to prevent any debris from entering the pump and causing damage to the impellor. If the strainer basket becomes damaged at all it should be replaced immediately.

The purpose of the skimmer is to allow just the very top of the pool water to flow in via a floating weir, and then any floating debris gets left in the skimmer basket ready for weekly emptying. Water is also drawn through the sump or low suction fittings. The flow valves control the flow from the skimmer to the sump so you can adjust to obtain the optimum suction for your particular pool.

The pump impellor spins causing a small vacuum. This slowly, providing the pipe work is water tight sucks the water from the pool into the pump pre strainer basket via flow control valves. Once the water has passed the impellor, the water is then under pressure and is pushed from the pump to the filter multi-port valve.

The multi-port valve now have 6 positions. The filter position is the position where the valve handle stays in most of the time. The water flows into the valve then the water flows into the top of the filter, being forced down through the media, leaving all small particles of dirt and debris in the media. The water passes through small slots in the pipes at the bottom of the filter called laterals. The water passes back into the multi-port valve then through the pipe work and back on to the rest of the system.

The Multiport Valve

This valve controls all water movement through filter.

  1. Filter: Water comes from the pool into the top pipe and the filter goes down through the sand and out from the lower pipe on the filter and back to the pool
  2. Waste: The water comes from the pool and goes straight to the drain bypassing the filter.
  3. Closed: Water will not pass through the valve.
  4. Backwash: The water comes from the pool into the lower pipe and up through the sand and out of the top pipe and off to waste. (This cleans the sand.)
  5. Re-circulate: The water comes from the pool and bypasses the filter and returns to the pool.
  6. Rinse: The water comes from the pool into the top pipe and down through the sand and out of the bottom pipe and off to waste. (This washes the last of the dirt out of the sand after backwash.)

N.B. Always switch off the pump when moving the multiport valve.

Filter

The filter removes particles of dust and debris that are in suspension in the water. For private pools during the bathing season it is necessary to pass the contents of the pool through the filter at least twice every day. As the water temperature rises and bathing increases, so does the necessity of running the filter for longer periods. Once the pool is up to temperature it is certainly recommended that the filter be run for at least 12 hours every day or enough to achieve two complete water turnovers.

It is strongly recommended that a time clock be fitted to the pump, which will ensure that this essential period of daily filtration becomes automatic.

The pool must always be crystal clear for safety reasons if the water becomes dull or cloudy and the pool chemistry is correct, then the filter should be run 24 hours per day until sparkling clarity is regained. A high wind or a bathing party will introduce an excess of debris into the pool and the pool water can go cloudy over night. Continuous filtration possibly with use of a flocculent will restore quickly the clarity of the water.

Because the filter takes out fine particles from the water it will become partially blocked after a period of time. On the filter is a pressure gauge. The pressure will rise as the filter becomes dirty and this indicates when backwashing should be carried out. Note the pressure when the filter has been backwashed and the media is clean, this is called the clean running pressure. When the pressure has risen by 5lb per square inch (PSI) above the clean running pressure, the water flow around the pool will be considerably reduced and the filter should be backwashed (see notes later). Regardless of pressure the filter should be backwashed at least once a week. You may find the filter starts to leak from around the top due to excess pressure.

Periodical chemical cleaning of the filter, by means of a proprietary filter cleaner is desirable for optimum performance. For cartridge and diatomaceous earth filters the procedures are different and the manufacturers instruction must be adhered to. The filter sand should be changed every 4/5 years to ensure effective filtering.

Heaters

Pool heaters, whether heat pump, gas, electric or oil, are fitted with a thermostat to keep the pool at a controlled temperature. Solar panels are controlled by a differential temperature control to activate the system whenever solar heat is available for collection. Heaters rarely give trouble but if you have one remember that these units require regular servicing and winterisation in the autumn to keep them in good condition and stop possible issues with freezing.

Temperature is very much a matter of personal preference, however in liner pools the recommended maximum temperature is 85F or 30C for the new super liner and 82F or 28C for the standard 30 Gauge liners. Overheating tiled pools can also be a concern, if the pool overheats the tiles have nowhere to expand and the tiles can pop off.

Trouble Shooting for Pool Heaters

Electric Heaters

  1. These heaters are usually on an economy electrical supply (economy 7) operated by a time clock. (A power cut may alter the time for switching on the unit). Check and reset the time if necessary.
  2. If the filter requires backwashing, only a small volume of water may pass through the heater and the built in safety device will trip the excess temperature switch. To restore the safety device, backwash the filter and reset the temperature switch.
    The heater will not operate if the thermostat is set at a lower temperature than the pool water.
  3. The pH level is very important with electric heaters so always regularly check and keep pH level at 7.4.

Gas Heaters

  1. If the filter requires backwashing insufficient water passes through the heater and the safety pressure switch will not operate. Backwash the filter.
  2. Pilot light blown out. Relight pilot.
  3. The heater will not operate if the thermostat is set at lower temperature than the pool water.
  4. New gas boilers are fitted with gas pressure switches so always ensure you have sufficient pressure before fitting a gas boiler.
  5. Always have your gas boiler annually serviced by a qualified engineer. This ensures your boiler is always performing correctly.

Oil Heaters

  1. Check the oil level in the tank. This seems obvious, but many calls are due to no oil.
  2. Check temperature controller.
  3. Check reset button on the burner.
  4. Always have your oil boiler regularly serviced by a qualified engineer. This ensure that your boiler always runs as efficiently as possible.

Heat Exchangers

  1. Check that boiler-supplying heat is operating.
  2. Check secondary circulation pump is operating.
  3. Check temperature controller.
  4. The pH level is also very important. High pH can cause scale to form in the heat exchanger and reduce the flow.

Heat Pumps

  1. Clean the air intake at regular intervals and always make sure that nothing is restricting the air outlet to ensure maximum air flow through the heat pump.
  2. If there is insufficient water flow through the heat pump it will cycle on and off, and the filter should be backwashed and pump strainer and skimmer baskets cleaned.
  3. If the unit is short of gas it will fail to operate and it may trip the high or low pressure switch. Contact a heat pump specialist and hw will service the unit and re-balance the gas pressure.

Solar Heating

  1. An adequate flow of pool water through the solar panels is necessary to ensure efficient operation. If the surface of the panel is not cool to the touch when operating in bright sunshine, this indicates inadequate flow, and the cause should be identified.
  2. No regular maintenance is required, except that if dirt accumulates on the panels, this should be washed off.
  3. Check solar control device.