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

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