PRB Articles

Troubleshooting Filters

No matter how much care is taken to operate a filtration system at its peak performance, there are times when the pool operator witnesses changes in water clarity. Additionally, the ability to see the main drain at all times is critical to safety, and is mandatory in all pool codes and regulations.

Troubleshooting the filters can be accomplished through a systematic observation of various instruments in the filter room. The purpose is to understand the key indicators through careful gathering of all information in order to take corrective action.

Know The Equipment

Two important devices register pressure and flow--the pressure gauge and the flowmeter. In most systems it is impossible to see inside; therefore, these devices indicate filtration activity so the operator can tell what is happening, or how dirty the filter is. Some filters are equipped with two gauges--the vacuum gauge (influent) and the pressure gauge (effluent).

There are two different filtration systems--pressure and vacuum systems. Most sand filters are designed as a pressure system where the pump forces water to be cleansed into the filter tank. When there is an issue with clarity, the pressure gauge will rise, indicating that the filter is becoming dirty; as the dirt gathers within the tank, it raises the pressure. Conversely, if there is no change in the pressure gauge, there is also a problem.

This is where troubleshooting becomes important.

Reading Gauges Properly

If the pressure gauge remains high--even after backwashing--the sand has absorbed excessive dirt or oils, and the backwashing must be continued; also, there may be a large deposit of calcium on the top of the sand bed, which impedes the flow. In both cases, looking at the sand and stirring it may eliminate this condition. Also, there are filter cleaners that may help in removing the oils. If the pressure gauge remains low, there is usually a blockage on the suction side of the pump; this may be in the hair and lint strainer basket, or leaves in the skimmer or over the main drain. If the pressure gauge remains low, perhaps the filter is being backwashed too frequently; not allowing the filter pressure to rise.

On those installations which have two gauges, influent and effluent, troubleshooting involves determining the difference in the readings between the gauges. When the filter is clean, the differential is low. Operators should note the reading on the clean filter gauges. When there is a difference of 8 to 10 pounds of pressure, the filters should be backwashed. If the gauges do not return to the original differential, further cleaning or inspection should be made.

Other gauge phenomena include observation of the needles. Are they steady or do they vibrate? A steady needle means the pump is operating at the right flow with little or no air in the system. A vibrating indicator may mean that air is trapped in the filter or circulation is inadequate. If the vacuum gauge is reading high, there is a blockage on the suction side of the pump.

The flow meter installed on the return line indicates the number of gallons per minute (gpm) that are flowing back to the pool. Most pool engineers design the pool operation based on a maximum- and minimum-rate of flow for each pool. This hydraulic design is calculated to achieve water clarity based on the size of pool. The filter is then sized based on the gallons per minute per square foot of filter surface area. If the flow indicator shows a reduction in flow, this may indicate the filter has not been backwashed completely. As the pump creates the flow, the operator should also inspect the pump impeller to determine if it is damaged or its operation is being obstructed by hair. Taking the pump apart and inspecting the impeller will determine corrective action.

Study Pool Water

Observations at the pool itself also may indicate a problem within the filter system. Is there sand or dirt in the pool? This indicates a broken under-drain lateral. In this case, the operator must remove the sand and replace the lateral. Are air bubbles or cloudy water observed at the return inlets? Perhaps the air is being collected in the filter system; usually this is due to the top of the hair and lint strainer being secured or the valves in front of the pump leaking or in need of repacking. Also, if the water level is lower--below the skimmer--the pump is sucking air. Another condition which may lead to air bubbles occurs during vacuuming. If the vacuum hose is full of air, it will travel through the system and back into the pool. Bleeding off the air-relief valve should eliminate the problem; however, if excessive air bubbles continue or there is excessive air in the filter tank, the operator should determine the cause of the air. Nine times out of ten, it will be on the suction side of the pump.

Other Filters

Troubleshooting pressure- and vacuum diatomaceous earth (DE) filters have a set of parameters different from those in dealing with sand filtration. The most common condition is that the pool water is not maintaining water clarity. The filter grids may be clogged with oils, dirt and minerals, which does not allow for DE or alternative media to adhere to the fabric. Another problem is powder backing into the pool. In these cases, the operator should visually inspect all the grids and take appropriate action, either cleaning the grids with an appropriate filter cleaner or replacing the grids that have been torn or damaged.

In a pressure DE system (the pump forces water into the filter), the filter-pressure gauge reads similarly to that of a sand filter. If the filter pressure is high, the filter grids are covered with oils, dirt and minerals, which are clogging the fabric. Most troubleshooting conditions are the same as with a pressure sand filter, when air bubbles or excessive media are backing into the pool; however, the operator should inspect the manifold for damage if unfiltered water is backing into the pool.

The troubleshooting methods of a vacuum DE filter create another set of indicators. As in the case of the pressure DE, if the water clarity is not being maintained, check the filter fabric on the grids for excessive oils, dirt and minerals; also check for inadequate power on the filter grids. If the filter pressure remains high, the operator should inspect the pit to ensure that pool chemicals--particularly calcium products--are not being fed into the media pit. If this is the case, the chemical induction lines need to be relocated to avoid filling the pit with chemicals. In a vacuum DE installation, the pump “sucks” the pool water through the filter system, the opposite of the pressure system. In this case, if air bubbles are coming back through the pool returns, the filter covering may be plugged, causing the pump to pull air from the weakest point in the system above water level. Also, a damaged manifold or blockage in the suction line to the pump may increase air.

The aquatic operator should understand and be fully aware of all the key indicators, gauges and meters, and their functions. In addition, logs must record daily activities, providing the operator with a history. Obviously, the operator must make sure the instruments are functioning and in good repair. In addition, recording clean pressure-gauge readings, the frequency of backwashing, the amount of DE powder for pre-coating the grids and flowmeter readings are all vital in the operator’s daily routine. Any change from the norm is the first step in troubleshooting. Action should be taken immediately to avoid future damage.

Connie Gibson Centrella is a professor and Program Director for the online Aquatic Engineering Program at KeiserUniversity eCampus. She was twice-honored with the Evelyn C. Keiser Teaching Excellence Award “Instructor of Distinction.” Centrella is an industry veteran with over 40 years experience in the pool and spa industry. She is a former pool builder with extensive knowledge in pool construction and equipment installation as well as manufacturing.

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