Your tank capacity ______________________
gallons
Your flow requirement ___________________ turns / minute
at a glance! The mixer to best suit your needs will depend on ten basic factors. One such factor is the amount of "pumping capacity" you will require. A simple way to understand this is by "turnovers per minute"...the tank capacity in one minute is "one turn". Two turns per minute in a 500 gallon tank would be 1000 gallons per minute in pumping capacity. One turn per minute is considered "mild agitation" which is used for liquid storage, pH adjustment, etc. 1 ½ to 2 turns per minute is considered "standard agitation", for blending and general mixing. Three or more turns could be used in solid suspension* or fast mixing applications and is considered "vigorous agitation."
Interestingly enough, you can achieve the same amount of liquid flow when using a 11" impeller at a speed of 1700 RPM (direct drive) as you can by using a 36" impeller turning at only 70 RPM. The difference is that it takes a 20HP motor to turn the smaller direct drive impeller while it only takes a ¾HP motor to turn the larger impeller. BIGGER AND SLOWER IS BETTER. Not only do you save an enormous amount of power but the slow speed also improves wear and tear and cuts your maintenance costs. The characteristics of the liquid(s) and materials you are mixing will determine how strong the mixer must be and what type of impeller you will need.
The dimensions and configurations of your tank or vessel will also dictate some of your agitation requirements. A tall, thin tank may require multiple impellers to get full top to bottom mixing. For standard blending, a ratio of 1 : 1 ½ tank diameter to straight side is ideal. If baffles are available, they should be about 1 / 12 of the tank diameter in width. If baffles are not available - as in most plastic tanks, the mixer should be placed off center about 20% of the tank diameter. The shaft length will be determined by the least amount of liquid you plan on mixing in the tank, which is called the "minimum bath level."
* For solid suspension, a coned or dished bottom should be used where possible. Obviously, the weight, size and amount of solids, and the degree of suspension that you require will determine the power and pumping capacity that are required.
The chemical make-up of the solutions being mixed will determine what the wetted surfaces should be. Check with Corrosion Resistant Technologies 800-245-3769.
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