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Comments on Other Mixing Technologies

Simple Inlet / Outlet Pipe Separation

    Just separating the inlet and outlet pipe may do nothing to solve water quality decay, especially in summer. Many state regulatory agencies now require separate inlet and outlets, which is a very good design goal. However, one needs to understand where the dead zones are, and also realized the dead zones move based on season and tank operation. The focus, however, needs to be on achieving complete mixing.

Mechanical Mixers

    Distribution tanks are designed to, and need to, fluctuate levels or turnover in order to minimize water age. Water levels drop during a draw, and the distribution pumps are designed to get the tank to high water, overflow, plus freeboard. So, there is an energy source already built in to the tank – that is differential pressure.

    What mechanical mixers do, whether they are solar, electrical, or batter powered, is add another energy source into the tank. What’s important to understand is there already is one – differential pressure. The problem in the past was single inlet pipes (whether common or separate from the outlet pipe) often could not mix tanks and prevent water quality deterioration. However, mixing is now well-understood due to the extensive amount of research and field validation so the existing differential pressure plus a properly designed multiport TMS achieves complete mixing and eliminates water quality problems, passively, without the need for an external energy source or maintenance. Consider, if a tank is filled with water and never turns over, all a mechanical mixer would do it mix continually aging water. So, maintaining water quality in storage tanks is a combination of tank turnover and a properly designed mixing system. The advantage with the TMS is, once it is installed, it never needs touched again – there’s no maintenance required.

    Mechanical mixers are indeed “mechanical” and have moving parts that need maintained. Access to the mixer is difficult and it would either need to be extracted from the tank, or men and equipment would need disinfected to go into the tank to work on it. In addition, mechanical mixers have appurtenances like electrical boxes and other equipment that gets mounted outside the tank, often on the roof of the tank. Additional penetrations are needed in the roof or shell of the tank to get wires/telemetry to the mixer. Appurtenances mounted outside of the tank are prone to damage from inclement weather, corrosion, vandalism.

    Other considerations of mechanical mixers that may warrant investigation are:

• Ability to get equipment thru hatches
• Having a power source at the tank
• Power cost
• Inspection and repair cost and downtime
• Interference with Cathodic Protection Systems and roof support columns
• Safety concerns with electricity
• Equipment mounted to roof – issues with welding brackets and burning coatings
• Roof/dome of tanks must be reinforced due to loads of roof-mounted equipment from wind
• Wires/cables are required to run thru shell or roof of tank. Any tank penetration is a source of potential contamination
• What procedures are required to protect equipment when completely draining tank?
• How do solar powered units work with prolonged overcast and winter conditions?
• The negative effect of inclement weather on solar panels, especially snow in cold climates
• Damage to solar panels from hail
• Ice layer can disturb the circulation patterns of solar powered mixers that rely on spreading flow radially on the water surface
• Potential ice damage to floating components
• Contamination of potable water from motors and components?
• Are all submerged components NSF61 certified including lubricants?
• Potential vandalism of components outside of tank
• Does it require factory installation? Does manufacturer have a contractor’s license in your state? This can potentially cause issues with labor unions.

US Patent No. 7,104,279
Canada Patent No. 2,409,009