Questions about the PAX Water Mixer

Q. How can this small impeller circulate millions of gallons of water so efficiently?

Q. Is there a limit to the size and shape of tank or reservoir that can be mixed?

Q. What is the difference between “Active” and “Passive” mixing?

Q. How long does installation usually take and what special arrangements do I need to make (i.e., do I need to drain my tank)?

Q. How long before we see results?

Q. Is the PAX Water Mixer an effective solution for standpipes?

Q. Is the PAX Water Mixer an effective solution for elevated tanks?

Q. Can the PAX Water Mixer be powered using solar panels?

Q. Does the PAX system download to SCADA?

Q. Where do all the savings come from?

Q. Has the product been installed and tested in cold environments?  Are there any ice concerns?  What operational complications would be caused at freezing temperatures?  What happens when ice begins to form inside the tank?

Q. Is it safe to use a submersible motor in drinking water?

Q. How are the feet attached to the floor of the tank?

Q. Does the product require continuous, full-speed operation or can the mixer be operated to optimize energy savings?

Q. How is mixer operation affected when water level declines? Is there a minimum water level?


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1. How can this small impeller circulate millions of gallons of water so efficiently?

The heart of the PAX technology is our unique Lily impeller –a compact but highly efficient design for moving large volumes of water. The PAX mixing impeller was designed using advanced computational fluid dynamics modeling to replicate the flow efficiencies observed in natural water bodies such as lakes and ponds. Never before has a device of this size been used to effectively mix volumes of this size.

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2. Is there a limit to the size and shape of tank or reservoir that can be mixed?

PAX has a range of products suitable for effectively mixing reservoirs up to 20 MG. Our 1/3 HP unit has proven effectiveness in reservoirs up to 10 MG. This includes very flat, shallow tanks and reservoirs that have poor circulation (even with separate inlets and outlets), as well as rectangular in-ground storage basins (including those with piers or columns) and standpipes. Higher power units (up to 3 HP) mix faster and can address larger volumes. Larger or more complex reservoirs can be mixed using multiple units. Please see our Case Studies in our Downloads page for more information on the types of tank geometries we have successfully mixed.

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3. What is the difference between “Active” and “Passive” mixing?

Active mixers are mixers that operate on solar or grid electric power and continuously mix tanks, day and night. Passive mixing systems rely solely on tank fill and drain cycles to provide mixing. Passive systems include tanks with separate inlets and outlets, and tanks with additional piping and nozzles inside the tank.

Passive mixers only work during fill cycles. During periods of low demand, passive systems often fail to fully mix a tank. Operators can artificially increase the turn-over in a passively mixed tank by drawing water from other tanks in the system, but this causes two problems. First; this excess pumping costs the utility more in electricity and increases a utility’s carbon footprint. Second; this approach requires additional operator time and input. Third; this approach limits an operator’s ability to respond to emergencies: operators may face periods when tank levels are artificially low.

Active mixers provide year-round, round-the-clock protection for all your tanks and allow you to keep maximum storage volumes on hand for emergencies, without sacrificing water quality.

Active mixers cost much less than passive systems. Total cost is typically less across all aspects of the project: including significantly less hidden costs for upfront initial design and engineering, a smaller capital cost (due to smaller equipment), and much less cost for site preparation both before and during installation. In some cases operations and maintenance of these passive systems can also cost more than maintenance on active systems (especially when labor and man-hours are considered).

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4. How long does installation usually take, and what special arrangements do I need to make (i.e. do I need to drain my tank)?

If the tank is full during installation, then the robust submersible system easily installs in three hours through a conventional hatch, requiring two technicians and a diver. If a diver is required but your utility does not currently have a relationship with divers, then PAX’s service team can help arrange the logistics to coordinate the installation.

If the tank is emptied, installation can be completed even faster by utility staff, avoiding the need for a diver and thereby reducing installation costs. No cranes are required, and there is less risk for injury during installation because of the compact design. No alterations to the tank or access hatches are required, and the mixer does not damage the coatings inside the tank or disturb sediment inside the tank. Operator time supervising the installation onsite is minimized because of the simple installation – a savings of both time and money for the utility.

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5. How long before we see results?

Thermal uniformity in a tank is usually re-established within the first 24 hours. Residual levels typically rise and stabilize over the course of days to weeks.

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6. Is the PAX Water Mixer an effective solution for standpipes?

Yes. The PAX Mixer can effectively mix standpipes up to 120 feet in height. This mixing prevents seasonal “inversions” and promotes residual all throughout the tank – even to the very top surfaces. Please see the Standpipe Case Study in the download section for a 3-page case study on a 1.3MG standpipe. If you have a specific inquiry about a particular candidate tank please email us at info@paxwater.com.

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7. Is the PAX Water Mixer an effective solution for elevated tanks?

Yes. The PAX Mixer can effectively mix elevated tanks – even with a central riser or support post in the tank. The power of the mixer allows it to be offset slightly from the middle of the tank, and still provide a complete mix. Whether the tank is 100,000 gallons or 2.0 million gallons, the PAX Mixer has been installed in multi-legged, spheroid, and hydropillar style tanks with the same results.

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8. Can the PAX Water Mixer be powered using solar panels?

Yes. PAX Water offers a solar power system option for off-grid installations or for those customers who are looking to reduce their carbon footprint. The size of the solar array will be fully customized according to your tank’s storage volume, location, and daily solar radiation, PAX Water has a network of reliable established regional providers with extensive experience in the solar photovoltaic industry.

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9. Does the PAX system download to SCADA?

Yes, there are SCADA connections available through RS-232 and through dry-contacts.  SCADA outputs allow operators to easily monitor the status of the mixer remotely from their computers.  Remote on/off functionality is also possible with the SCADA addition.

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10. Where do all the savings come from?

The energy and chemical savings anticipated combined with reduced labor costs lead to an average estimated payback period of under 4 years! Major components of these savings include:

  • Reduced pump energy costs and reduced carbon footprint associated with deep cycling.
  • Reduced costs associated with periods of comprehensive water quality monitoring, sampling, and testing in poorly circulated systems.
  • Reduced “breakpoint” or emergency chlorination, saving both labor and chemical costs.
  • Reduced sedimentation and biofilm formation lead to less frequent tank cleaning and other preventative maintenance.
  • Reduced flushing activities, and reduction in attendant costs.

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11. Has the product been installed and tested in cold environments? Are there any ice concerns? What operational complications would be caused at freezing temperatures? What happens when ice begins to form inside the tank?

The PAX Water Mixer is currently undergoing extensive testing in extremely cold environments for prevention of ice formation and the damage it causes to tank internals and coatings. Unlike conventional mixers which suffer from freezing of the exposed moving parts, the PAX Mixer is located at the bottom center of the tank. Data from mixing studies at warmer temperatures suggest that the circulation pattern set up by the PAX mixer will dramatically reduce the formation of ice inside tanks in cold climates.

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12. Is it safe to use a submersible motor in drinking water?

Yes! Submersible motors have been used in well pump applications for years without cause for concern. The PAX motor’s windings are completely cast in stainless steel, and the German design is water lubricated and water cooled, eliminating the chance of contamination from a broken seal. In addition, because the PAX design uses a bottom-mounted, submersible mixer, it protects the motor in cool water from the harsh and corrosive environment typical in the head space of storage tanks.

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13. How are the feet attached to the floor of the tank?

The feet are not attached to the floor of the tank. They are constructed of heavy weight rubber. These non-skid, non-scratch feet are gentle on the tank’s interior coating and, combined with the weight of the mixer, prevent the mixer from moving. In elevated tanks which have sloping floors we install rubber feet with a tie-down to prevent the mixer from sliding.

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14. Does the product require continuous, full-speed operation or can the mixer be operated to optimize energy savings?

PAX can work together with you to establish the optimal RPM for your tank. This will allow for the most energy-efficient usage and allow you to have 24 hour per day mixing in the tank. This continual circulation provides you the ultimate protection in all pockets of your tank. Passive solutions or solutions that only operate a few hours per day are intermittent solutions and provide less protection than full-time mixing.

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15. How is mixer operation affected when water level declines? Is there a minimum water level?

The mixer and tripod are approximately 4 feet tall. For the mixer to work most effectively there must be a minimum of 8 feet of water in the tank, to cover the impeller and allow the mixer to set up a toroidal flow structure and break established thermoclines. At levels less than 8 feet, localized mixing continues but the capability to circulate larger volumes is limited. The mixer will turn off if water levels fall below the impeller. The tank can be completely drained at any time — the PAX tripod design remains stable and will not damage the tank interior.