Reader Forum

I have a comment concerning the Simple Solution, "Agitating action," (PE, May 2001, p 12).

Using air to mix a vessel has been around as long as I've been practicing, and that's 42 yr. If one follows the drawing shown, all you get is a single stream of air bubbles. With the holes in the top, the sparger fills with the fluid. When the air pressure is applied, it blows the fluid out of the sparger until the first hole is reached, the seal is broken, and all of the air pressure goes out the first hole.

The correct way is to drill the holes in the bottom of the sparger. In this position, when the air is applied it rises to the top of the sparger and expands. This action forces the fluid out the bottom holes and then flows out the bottom.

Another reason why the holes should be in the bottom is that when the vessel is drained, no fluid is held in the sparger. —Avrum Silverman, PE, Project EngineerRV & Associates, Wellesley, MA

In the April 2001 issue, there was a question in the "Simple Solutions" column regarding getting a fish tape through an aluminum conduit.

Blowing a nut through the conduit with high-pressure air may not only damage the inside of the conduit, but may also create a hazard for anyone in the vicinity of an opening in the conduit. There are several available products to accomplish this task. Check with your local electrical supplier for a device called a conduit mouse. This is a small, sponge rubber slug sized for specific conduits. Also available are these same units in specific sizes with a string package attached. These work very well, but must also be used with caution as they reach a significant velocity and will exit the conduit on the downstream end and smack anyone standing there! We have had people injured by putting a finger in the conduit to stop it at a specific location or to divert it out of the conduit. —Tim Strom, Maintenance Planner, Longview Fibre Co., Longview, WA

The article on "Centrifugal air compressor basics" that appeared in the June 2001 issue of PLANT ENGINEERING had a formula on page 35 for converting standard cubic feet per minute (scfm) to actual cubic feet per minute (acfm). The way the formula was presented has caused some confusion to our readers. A clearer presentation of the formula would be:

acfm = (scfm)(Pstd) X T1

P1-Psat1 Tstd

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