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Filtration maintenance procedures

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A typical commercial pool containing 567,812 L (150,000 gal) needs a six-hour turnover rate. filtration
A typical commercial pool containing 567,812 L
(150,000 gal) needs a six-hour turnover rate.

A technician can determine what a system is currently doing (and what it is capable of) using the following procedures.

 

  1. Backwashing the filter as prescribed by the manufacturer.
  2. Attaching vacuum and pressure gauges to the pump.
  3. Converting vacuum and pressure readings to TDH using the formula: vacuum x 1.13 pressure x 2.31. By applying TDH to the manufacturer’s curve for the existing pump will give a technician the flowrate at its maximum with a clean filter. This should not exceed the maximum flowrate of the filtration system.
  4. Adding 7 metre of head (23 feet head) to the TDH will give the flowrate of a dirty filter. It is important to ensure it does not drop below the minimum flowrate required to meet the necessary turnover rate as well as the minimum required flow for the pool’s other equipment, including heaters, skimmers, sanitizing system, etc.

What are the options?

  • Change the pool pump to one that better fits the flowrate requirements.
  • Add a VFD that is capable of holding a constant flowrate to compensate for TDH changes during the clean to dirty filter cycle.
  • Add additional filtration (i.e. additional filter or larger single filter).

Note: Of these three options, the addition of a VFD is the only one that will actually pay for itself over time in energy savings.

Keep in mind, an oversized filter with a smaller horsepower pump can improve filtration but cause other problems. A typical example of inadequate backwash time or flowrate will show up when the system is put back into filtration mode. When a sand filter is not properly backwashed, a small amount of debris (silt) will come out of the returns for the first few minutes after returning the system to normal filtration mode. Some of the silt will also remain in the filtration system, working its way deeper into the sand bed. This can lead to costly service, repairs, or even premature replacement of the filter.

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