Be sure to:
Watch your pressure. If possible, test with your unit at various pressures to find the optimum combination or cleaning effectiveness, liquid consumption and washing time.
Size the unit appropriately. Use at least 0.15 gpm per square foot of interior surface. Maybe even 0.2 gpm or more is appropriate if your system can support it.
Make sure your equipment can take water out of the tank as fast as you need to put it in. Once you determine how much liquid you need to put in the tank to clean it, make sure the liquid can drain just as quickly. If the tank floods, it will reduce the cleaning effectiveness.
Do not waste coverage where it is not needed. If you do not need to wash the top, buy a unit that does not spray straight up. This will concentrate the washing liquid where it will do the most work.
Count the number of nozzles. Look for a head with three to five large flat fan orifices. These will minimize atomization and loss of impact. Turn away from slit or solid-stream orifices for these more difficult applications.
Very difficult applications. An example of a tough application includes the removal of latex residue from a reactor, especially heat-transfer surfaces. The material does not dissolve readily and impact is the principal way to remove it.
For very difficult cleaning processes, everything has to work its best. Limits likely exist on the amount of liquid you can use, so look at the trade-offs carefully.
This type of job is too difficult for free-spinning units, especially those with ball bearings. Look for something with controlled rotation. Solid-stream nozzles will make "stripes;" you need full coverage, preferably with flat-fan nozzles. Most of the same points for moderately difficult situations apply.
In addition, you should:
Consider a tank-washing machine using large solid streams.
Keep in mind that the impact will be enhanced if the amount of water is increased instead of the amount of the pressure. However, the larger the tank washer, the better it can tolerate and profit from high-pressure liquid.
If possible, consider hot water and available cleaning chemicals. Both can augment nozzle performance and make the task more manageable.
Tank washing or a clean-in-place (CIP) system can benefit from an appropriately chosen tank-washing nozzle. Many facets of the selection process are dictated by the nature of the cleaning requirements in your plant.
The first and most critical step is a thoughtful analysis of the specific cleaning task. This begins with an understanding of the nature of the "soil" and how it interacts with the cleaning solution. That knowledge will dictate the amount of cleaning solution and the best way to apply it for maximum effectiveness. From that point, the tank washer selection is much easier, and your probability of success will increase dramatically.
Welander is engineering director of Lechler Inc., St. Charles, Ill. Contact him at (800) 777-2926.