Resources | Mixer FAQ

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

2. Can the PAX Water Mixer circulate the entire storage tank, even the bottom 3 feet of the tank?

3. How can a small 8-inch impeller circulate millions of gallons of water?

4. What is the difference between “active” and “passive” mixing?

5. How is the PAX Water Mixer installed? Do I need to drain my tank or make tank modifications?

6. Does the PAX Water Mixer need to be installed in the center of the tank?

7. How does the PAX Water Mixer stay in place? Does it need to be fastened to the tank floor?

8. How long before I see results?

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

10. Does the PAX Water Mixer come with chemical feed options?

11. Does the PAX system download to SCADA?

12. Is there a minimum water level for operating the PAX Water Mixer?

13. Has the product been installed and tested in cold environments?

14. Does mixing help reduce disinfection byproducts like THMs?

15. What is the maintenance of the PAX Water Mixer and how long will it last in the field?

16. Will mixing improve my chlorine residual?

17. I’ve installed a mixer in my tank, how do I know it’s working?


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

PAX Water has a family of active mixers that have been successfully installed and operated in a range of tank geometries and sizes. A single impeller mixer can effectively circulate reservoirs up to 25 MG and larger volumes can be mixed using multiple units. This includes complex designs, such as rectangular in-ground tanks with supporting columns and 120-foot-tall standpipes. Learn about our family of active mixers here.

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2. Can the PAX Water Mixer circulate the entire storage tank, even the bottom 3 feet of the tank?

The PAX Water Mixer circulates the entire tank, top to bottom – including the bottom 3 feet of the tank. PAX Water collects temperature and residual data measurements from multiple water levels in the tank to verify mixing performance. Read our Redwood City, CA case study here.

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3. How can a small 8-inch impeller circulate millions of gallons of water?

The heart of the PAX Water Mixer is our unique Lily impeller – a compact but highly efficient design for moving large volumes of water. The Lily replicates the vortex flow pattern observed in natural water bodies – such as lakes and ocean currents – the most effective and efficient method for mixing fluids while using very little energy. Learn about the design of the Lily impeller here.

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4. What is the difference between “active” and “passive” mixing?

A passive mixing system can be a tank with a separated inlet and outlet or a set of piping and nozzles inside the tank that direct jets of water during the fill cycle. Passive mixing systems solely rely on tank fill and drain cycles to provide momentum for mixing. During periods of low demand, when mixing is most needed, passive systems often fail to fully circulate a tank. Active mixers operate on electric grid or solar power to continuously mix tanks, day and night, year-round. This continuous mixing provides the most complete and thorough mixing for tanks and allows operators to keep tanks full without sacrificing water quality. Learn more about the difference between active and passive mixing here.

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5. How is the PAX Water Mixer installed? Do I need to drain my tank or make tank modifications?

PAX Water Mixers are easy to install and maintain – no heavy cranes, lifting equipment or tank alterations are required. Before a mixer is installed, PAX Water recommends that the tank is drained, inspected and, if necessary, chemically cleaned – this returns the tank interior to its original as-built condition and ensures the best possible water quality. If a municipality prefers to keep their tank full, PAX impeller mixers can easily be lowered through the tank hatch or installed by a diver. PAX jet mixers are also lightweight and easy to install by lowering the unit by the powercord through the hatch of the tank.

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6. Does the PAX Water Mixer need to be installed in the center of the tank?

The PAX Water Mixer provides thorough mixing when installed below the hatch of a tank, even when the hatch is far from the center of the tank. Mixing performance will differ by no more than 20%, depending on the position of the PAX Water Mixer in the tank.

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7. How does the PAX Water Mixer stay in place? Does it need to be fastened to the tank floor?

The PAX Water Mixer does not need to be attached to the floor of the tank. Each impeller mixer has three “gecko” feet – made of a durable, NSF-certified rubber – that grip onto the tank floor and keep the mixer stationary while remaining gentle on the tank’s interior coating. In tanks with a sloped floor, the mixer can be tethered to the tank floor.

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8. How long before I see results?

Thermal and chemical uniformity in a tank is typically established within the first 24 hours of mixer operation and will vary based on the tank shape and size.

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

PAX Water offers a solar-power option for off-grid installations. The size of the solar array will be customized according to your tank’s storage volume, location and daily solar radiation.

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10. Does the PAX Water Mixer come with chemical feed options?

PAX has several options for introducing disinfectant into the jet of the mixer. PAX also has systems that can automatically monitor and dose tanks to keep disinfectant at a constant level.

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11. Does the PAX system download to SCADA?

The PAX Water Mixer has SCADA connections available through RS-485 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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12. Is there a minimum water level for operating the PAX Water Mixer?

The PAX Water Mixer is 4-feet-tall and will turn off if the water level falls below the impeller (doesn’t apply to jet mixers). For the impeller mixer to work most effectively, we recommend a minimum of 6 feet of water in the tank to cover the impeller and allow the mixer to set up a vortex flow structure. PAX also has a horizontal mixer that is ideally suited for shallow tanks.

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13. Has the product been installed and tested in cold environments?

PAX Water Mixers have been installed and operated in extremely cold environments (with temperatures as low as -40 °F) and are very effective at preventing ice formation inside tanks. Read our success stories on ice prevention here.

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14. Does mixing help reduce disinfection byproducts like THMs?

A powerful active mixer with help remove some DBPs from your water storage tank. Active mixing circulates water that is high in DBPs to the water’s surface, where they are exposed to air in the headspace of the tank. PAX has installed systems where active mixing and ventilation alone are able to max a significant impact on DBP removal. Read our Monterey, CA case study here.

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15. What is the maintenance of the PAX Water Mixer and how long will it last in the field?

The PAX Water Mixer requires very little maintenance. Impeller-based mixers come with a standard 5-year warranty and jet mixers come with a 3-year warranty. The majority of our impeller mixers (first installed in 2007) are still operating, so we advise customers to run the mixer to failure and then call PAX for a motor replacement.

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16. Will mixing improve my chlorine residual?

Strong active mixing can help reduce residual loss in tanks. When tanks are unmixed, they become thermally and chemically stratified, which promotes the development of bacteria and biofilms in the upper portions of the tank. This biological growth can exert a high demand on residual disinfectant and we have often measured upper water layers with zero residual. Active mixing helps bring fresh, disinfectant-rich water entering the tank into the upper water layers, which combats bacterial growth and biofilm formation. Strong active mixing also brings cooler water to the top of the tank, which slows the rates of chemical reactions that deplete disinfectant residual. Read our success stories on mixing preventing residual loss here.

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17. I’ve installed a mixer in my tank, how do I know it’s working?

Normal operation of the mixer can be confirmed by measuring electrical current draw or the readout from the power control center. Additionally, depending on the location of the mixer, you may see gentle swirls of current as you look down from the hatch into the water, such as around the interior ladder (if one exists). These currents are a visible indicator of the strong convection created by the mixer.