Mixers and agitators offer a unique problem for mechanical seals. Because most mixers or agitators are mounted on top or on the side of a vessel the long shaft being used to mix or agitate usually has an issue with run out. The longer the shaft the bigger the run-out.
Mixer and agitator seals are similar to pump seals with one major exception, they are more prone to shaft runout. The reason is the generally long shaft extension that gives the shaft leverage against bearings and seals. One solution is to mount the seal faces in a fashion that allows run out. Our type 19 seal is unique in that the dual seal rotary seal faces run next to each other against a single stationary. This is a very unique design that permits far more runout than traditional single cartridge or double cartridge seals . If the shaft is short or very well supported by ultiple bearings restriciting runout, a type 19 may not be necesssary.
Another issue with Agitator and mixer seals is they often do not receive lubrication. In the right conditions a mechanical seal can operate dry but key issues must be considered:
How much heat is being generated by the seal faces? The speed of the shaft and the materials of construction of the mechanical seal are of even greater importance than a flushed/lubricated seal.
The best combination of seal faces is Carbon Vs. Silicon carbide due to the low friction generated between these two faces. Glass filled PTFFE faces are another potential solution.
Chemical compatibility of the product being sealed must of course be considered.
If conventional double seal with environmental controls are utilized caution must be taken to be certain enough lubrication is provided without contamination of the product being mixed.
The determination if a seal like a type 19 mixer seal is required depends on several factors. You must consider the run-out of course which should be measured with a dial indicator. If the run-out is greater than 0.005" a seal designed for higher run-out should be considered.
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