Excessive water flow
Accelerated water flow can also cause channelling. If the water runs too fast and under too much pressure, it will come out of the diffuser, hit the side of the tank, and run all the way down—rather than spreading over the surface of the sand bed.
To check the flow rate, it is recommended to attach a vacuum and pressure gauge to the pump, then convert the vacuum and pressure reading to total dynamic head (TDH). Applying the TDH to the manufacturer’s pump curve will determine the flow rate at its maximum with a clean filter. If the maximum flow rate exceeds that of the filtration system, there will be too much water flow through the filter.
To take control of the water flow, facilities will benefit from having a variable-speed pump. This will allow pool operators to run the water at lower speeds, thereby maximizing the efficiency of the filtration system and increasing the speed allowance for backwashing.
Conclusion
To keep filters working in their peak condition, operators must prevent channelling in the sand media by ensuring proper backwashing and water flow. By doing frequent visual inspections inside the filter, running complete three-minute backwashing cycles, and confirming the water flow from the pump is appropriate, commercial pool operators should be able to maintain cleaner, clearer, and safer water, and avoid expensive filter repairs.
John “MacGyver” Watt has spent the last 25 years working for Pentair in a variety of positions, including field service technician, regional service manager, national trainer, and product specialist. He now works for Pentair’s application engineering and new product development for the U.S., Canada, and Latin America. He can be reached via email at john.watt@pentair.com.
