Regenerative Media Filters

Project managers should specify regenerative media filters that precoat in a closed loop and filters that precoat in the filter mode as equals. All regenerative media filters are required to automatically regenerate or “bump.”  The swimming pool contractor will have the option to what filtration system to provide.

PMs should use Nemato’s Atlas filter as the basis of design when completing the design data and mechanical room layout due to their larger size. MEP requirements for Neptune Benson’s Defender filter should be coordinated within the design team because it has greater electrical infrastructure requirements.

Regenerative media filters are NOT approved with manual valves because of the possibility of introducing media back to the pool if the valves are not sequenced properly.

Regenerative media (RM) filters are any filter system which reuses the media without the need for backwashing. The operation of the system follows the same mode as most other filters during filtration.  Water passes through media to remove particulate matter.

  • The RM filter system goes through four (4) different phases or cycles:
    • Off Cycle – Nothing happens.
    • Pre-Coat Cycle – The first cycle of operation of the RM filter system where the filter elements are coated with the filter media. The recirculation pump is operating, but no water is being used from the pool.  The pre-coat cycle lasts from 5 to 20 minutes.
    • Filtration Cycle – The pool water is being filtered.
    • Regeneration Cycle – Once the filter is fully charged and this can be based on differential pressure or time. The system will regenerate.  This recirculation pump turns off and the filter media is removed from the filter elements either by gravity or forced off by mechanical means.  The mechanical means are typically referred to as a “bump”.


  • CH calls filtration rates for various types of pools based on the following recommendations:
    • Outdoor Leisure Pools (water depths less than 4 feet): 1.0 to 1.2 GPM/ft2
    • Outdoor Multi-Purpose Pools (varying water depths): 1.0 to 1.4 GPM/ft2
    • Outdoor Competition Pools: 1.2 to 1.4 GPM/ft2
    • Spraygrounds / Tot Pools / Spas: 1.0 to 1.2 GPM/ft2
    • Indoor Leisure Pools: 1.0 to 1.2 GPM/ft2
    • Indoor Multi-Purpose Pools: 1.2 to 1.4 GPM/ft2
    • Indoor Competition Pools: *1.5 GPM/ft2

*Filtration rates higher than 1.5 GPM/ft2 can be considered on a per case basis depending upon the expected pool use.


The pre-coat cycle is the default starting point for all RM filters.

The pre-coat loop is typically two (2) pipe sizes smaller (but not less than 3” or greater than 8”) than the pressure (return) pipe to the pool. THE PROJECT MANAGER NEEDS TO CONFIRM THE PIPING SIZE REQUIREMENTS WITH THE BASIS OF DESIGN FILTER MANUFACTURER.

The hair/lint strainers should be a full port strainer. NO eccentric reducers should be used at the strainers.  Since the pre-coat tee is connected after the strainer and before the pump, an eccentric reduced strainer may cause cavitation or exceed the maximum suction piping velocity.

The RM filter media can be diatomaceous earth (DE), perlite, or cellulose. At this time CH is not recommending cellulose as an alternate filter media.

Perlite (purified volcanic ash) which has been approved by NSF for use in pool filters.   Perlite does not require a solids interceptor and can be discharged directly into the sanitary waste.  It has similar filtering characteristics to DE, but it is environmentally friendly.  Cost is comparable to DE media as well as filtration results.

Perlite is not as effective as DE. Perlite is degraded after each bump cycle no matter what RM filter is used.  (Even “clean” bumps degrade perlite.)  The more bumping means that the more perlite will float in the filter (i.e. ineffective media) and the more media will clump together.  The more the media clumps, the more that the precoat is inconsistent.  Depending on the designed precoat thickness, you could very well expose some of the elements over time.

If insufficient perlite media is in the filter cloudy water conditions can occur.

Perlite has been used for years in municipal wastewater and other industrial applications. Historically, the pool industry has received the rejected perlite that is not good enough (i.e. inadequate perm ratings) for these other industries.

Neptune Benson calls for a perm rating (or Darcy ratings) of at least 1.7.

Nemato uses a media source that will supply perlite with a rating of 3.25. The higher the perm rating, the more voids the media will have in it to capture dirt, particulate, etc. resulting in better filtration and less clumping.  This perlite is Tech-Flo 2000x provided by Industrial insulation.  The other significant benefit of this perlite is that it has virtually no float.

The Defender system requires a periodic chemical cleaning to remove spent media and oil left on the elements. Depending on the filter loading and pool usage, this should be planned for at least one time per year.  This process requires the filter system to be off-line 24 – 36 hours.

RM filters require clearance over the top of the filter for head removal and maintenance. The project manager should confirm that the minimum requirements for overhead clearance above the filter tanks are met.

  • Normal flow operation of the filter system will operate via hydraulic pressure supplied by the recirculation pump. However, the RM system must have the following devices included:
    • Control Panel – The Defender control panel requires a 30 amp, 110 VAC circuit to each filter to power the control mechanism for the filter. The Defender control panel can be remotely located from the filter tank.  However, it is the preference of Neptune-Benson to have the unit mounted to the filter tank.  Nemato’s control panel requires a 15 amp, 115V power supply.
    • Vacuum Transfer Pump – 1.5 hp TEFC 115/230 V, single phase motor draws the media from the bag and discharges into Defender tanks. Nemato’s vacuum transfer system requires 115V, 7.8A power from the control panel.
    • Air Compressor (Defender ONLY) – 2 hp, 120 V, 1 phase, 15 amp, 5.5 CFM at 90 PSI air compressor with a 30 gallon storage tank drives the “bump” mechanism and control valves. Only one (1) air compressor is required for most operations.  If multiple filtration systems will be used, either additional storage capacity or a large compressor may be required.  Consult with Neptune-Benson.
    • Variable Frequency Drive / Soft-Start Motor Starter – The Defender system requires a minimum soft-start motor starter to be provided for the recirculation pumps. However, the preference is for variable frequency drives.  CH requires VFDs on ALL regenerative media recirculation pumps regardless of the manufacturer.
    • Waste Piping – The Defender system uses a gravity drain to waste the media. An interceptor pit should be required for DE media (Perlite is not required).  Also, the International Plumbing Code requires an air gap on the discharge line of the filter.  Nemato’s Atlas filters are NSF approved to backwash under gravity or pressure.  Their recommendation is to backwash under a pressure of 0.8 GPM/SF.
    • Atlas filters include a “media release accelerator” which is used for the “bump” cycle. This vibration only lasts 20 seconds for a backwash and should be done twice.
    • Air Relief Piping – The Defender requires a couple service valves to remove the excess air from the filter tank and to aid the removal of the media from the filter tank. This service valve should be located as close to the control panel as possible.  The air relief piping should be routed to waste (not to a floor drain).
    • If a UV system is used with Defender filter system, the UV bulb may overheat during regeneration cycle requiring a manual restart of the UV system. To avoid this, an interlock between the UV and the filter control panel is required so that the control panel shuts down UV during regeneration and restarts at completion of pre-coat.  These systems are tied to the wiring box at the chemical controller.
    • For Defender filters, a check valve on the suction line is only required for a self-priming pump system or a straight centrifugal pump system where the pump is above the equalized level.  This could cause air induction and turbulence in the filter which will interfere with the proper coating of the elements.  Pump systems that remain in a flooded suction condition would not require a check valve.


Defender filters should be designed with a 10-12 psi differential (28 TDH) and a maximum of 32 TDH.

Some counties and states require pearlite to be separated and removed before backwashing regenerative media filters to sanitary. Check local codes regarding this requirement. When this is required a custom separation, screen to be manufactured by Neptune Benson. It is recommended the separation screen to be capable of filtering to 10 microns.

Illinois Department of Public Health (IDPH) has required the addition of a solid’s interceptor for any manufacturers Regenerative Media Filter. They state that if in the future the owner decides to change media, the system will be capable of handling either media.

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