The filter is designed to remove suspended solids from the pool water. For domestic pools where bathing loads are light, the pump will circulate the pool water through the filter every eight hours. For pools with higher bathing loads the circulation rate is higher, typically four to six hours.
Pressure Sand Filters
These are the most commonly used filters in Kenya. Dirt and other deleterious materials are removed from the water by forcing it through the filter media, which consists of layers of carefully graded river sand. Pressure sand filters are rated according to the volume of water passing through every hour divided by the effectiveness of the filter media. Modern fiberglass filters are effective with a flow velocity of up to 50 m/hr.
Maintenance of Filters
Dirt removed by the filter will accumulate in the filter media and this eventually leads to clogging. The larger size filters have a pressure gauge on the inlet, which can be used to access whether the filter media needs cleaning. When the filter is operating effectively the operating pressure will typically be between 0.6 and 1.0 bar (10 to 15 psi). As the filter becomes blocked the pressure will rise and an increase of 0.3 bar (5 psi) indicates that it should be cleaned. This will involve backwashing and rinsing (for pressure sand and DE filters) or hosing down of elements (for cartridge filters). If no pressure gauge is supplied then the filter should be backwashed on a regular basis, normally once a week being sufficient.
Use of Multi-Port Valve (MPV)
Most modern filters are fitted with a multi-port valve (MPV) to simplify filter operation. There are six positions on the MPV and the various operations possible with the different settings are described below.
MPV Operation
Filter
This is the normal operating position. Water from the pump is fed into the top of the filter and after filtering through the media is collected at the bottom. It is then returned to the pool through the inlet pipes.
Backwash
When the filter becomes clogged, the MPV should be turned to BACKWASH. Water will now be pumped from the pool into the bottom of the filter and out of the top. It is then discharged to waste. This operation normally takes two to three minutes and should be continued until the water in the sight glass on the side of the MPV is clear.
Rinse
After backwashing the filter media needs to be rinsed. Water is pumped into the top and out of the bottom of the filter as for normal filtering but the water is then discharged to waste. This removes any residual dirt in the media instead of pumping it back into the pool. Rinsing should not take more than one minute and again the sight glass on the side of the valve can be used to see when the water is clear.
Recirculate
In this position the filter is by-passed completely and the water is pumped straight back into the pool. It will normally only be necessary to use this option if there is a problem with the filter itself (e.g. a leak or a major blockage). It can also be used if the filter is on a spa bath to increase the pressure at the hydro-jet inlets.
Waste
The waste port is used for emptying the pool. The filter is by-passed and water is taken straight from the pool to waste. If it becomes necessary to empty the pool make sure that the pump is not switched off once the operation has began as there may be problems with priming the pump when the water level is low. This position can also be used for vacuuming to waste. This may be necessary if there is a large amount of sediment on the floor of the pool, which would rapidly clog the filter in normal operation.
Closed
This shuts off all flow to the filter and the pool. It is usually used in conjunction with the valves on the suction side of the pump to prevent water loss when it becomes necessary to remove the lid of the line strainer to clean the basket.
WARNING: WHENEVER THE POSITION OF THE MPV IS CHANGED THE PUMP MUST BE SWITCHED OFF OR THE MPV MAY BE DAMAGED.