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Filtration pressure and cleaning

Like any filter, once it gets dirty, it needs to be cleaned to continue to operate properly. Filter pressure is one of the best ways to determine if the media is dirty and needs to be cleaned. The change in pressure differential (pounds per square inch [psi]) can help a service professional determine if a filter is dirty or needs to be backwashed. For this type of information to be effective, it is helpful to keep a filter pressure log for each pool. Many service technicians do this when opening the pool, leaving the information posted near the filter in the pump room or by logging it into the customer’s pool chart.

One of the most important figures to note is the initial pressure on the gauge at the top of the filter tank. If a pool is having trouble with water turbidity, or with the heater cycling while trying to maintain the proper water temperature, service techs can start their diagnosis by looking at the filter pressure reading. If, for example, the pressure reading at pool opening was 124 kPa (18 psi), but now reads 207 kPa (30 psi) when the trouble is occurring, the first thing a tech should consider is a dirty filter. In this case, the filter should be backwashed to see if it fixes the problem. By restoring the water flow, it allows the filter to function properly, which should allow the water to clear and might even fix any problems with the pool heater. As mentioned earlier, when the filter pressure goes up the flowrate goes down. A lack of water flowing through the heat exchanger allows the water to absorb too much heat and, as a result, it triggers the shut off on the high limit safety circuit built into the heater.

However, a newer challenge has presented itself now that variable-speed pumps (VSPs) have become extremely prevalent on today’s pools. In the past, the pump was either on or off and service technicians took the pressure measurement when the pump was on. That said, VSPs do not constantly run at full speed, which makes it harder to obtain an accurate reading. In the case of VSPs, the flow and pressure increases, but not necessarily because the filter is dirty. To overcome this issue, many service techs today turn up the pump to the highest pre-set circulation speed (not the highest speed on the pump) and take a pressure reading during their weekly service. Those that are not performing a weekly service often ask their customers to look at the reading and call the pool service company if the pressure increases by more than 69 kPa (10 psi).

Running the pump at the highest pre-set circulation speed and checking filter pressure is part of the weekly service routine, along with cleaning the filter baskets, skimmers, etc. Cleaning the filters when there is a
69 kPa (10 psi) increase is especially important with cartridge and DE filters as it can prolong the equipment’s life. Following this procedure will help avoid compression and compaction of dirt and debris on the face of the grids and/or cartridges, making them last longer and easier to clean.