On a regular basis, I get calls and questions from processors who are trying to figure out why their conveying systems aren’t working as expected. In a number of cases, the problem turns into one of distance.  The system can convey material from one location, but can’t pull a similar amount of material from a location that, to the naked eye, appears to be about the same distance away.

The situation doesn’t make much sense until you consider that when you are conveying material, distance is not something that you can calculate with a tape measure alone.  Instead, you’ve got to calculate the “equivalent distance” from the standpoint of the vacuum pump. That pump is being asked to provide the vacuum needed to lift and suspend large amounts of material in air, along with the airflow (CFM) needed to move all that suspended material to another location.  It’s got to be sized to do the job over the longest distance (source to destination) in the system.

When calculating “equivalent distance” for conveying resin, different features of your conveying system add different amounts of distance, which together can add up to a lot.  Let’s consider this example, which involves moving material 200 feet across a facility:

Start with horizontal feet of conveyor line

200 ft.
If the horizontal line is mounted overhead, multiply vertical feet x 2 and add. 20 x 2 = 40 ft.
If the lines contain 90° bends, multiply the number of bends x 20 feet and add. 5 bends x 20 ft. = 100 ft.

If you use a 15-ft flexible hose and a wand to pick-up resin from a Gaylord at the source point, multiply feet of hose x 3 and add.

15 x 3 = 45 ft.

(Note: the equivalent distance added by flexible hose varies based on hose size and construction.)

Total equivalent distance:

200 + 40 + 100 + 45 = 385 ft.


I’m sure that you get the picture. In this example, the equivalent distance that resin must move is nearly twice the actual distance across the plant. The point is that efficient conveying requires careful system design and attention to all the details, since even a few features can make a big, big difference in the “equivalent distance” for conveying and the amount of work that a vacuum pump must perform

When conveying, “equivalent distance” matters

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