How Can I Get More Vacuum Where I Need it?

Consider this – you have just bought a new vacuum pump and you have determined that your vacuum lines are sized properly, but for some reason, one or two lines are just not performing at the levels you expected. Is there a solution to this problem? Yes there is! It is all about distributing the vacuum to where you want it.

If all of the vacuum lines are the same size and if all of the vacuum lines run directly to the releaser, then all of the CFMs for each line will be distributed equally across the system. If you have 4, 1 inch lines coming to a releaser powered by a 60 CFM pump, then each line would receive 25% of the vacuum or 15 CFM. According to theory that would be enough vacuum to run 1500 taps on each line. However, based on previous articles in this blog you realize that due to line loss this is not entirely true, but each line would still receive 25% of what is available. What happens when you have 1, 1 ¼ line used in a Wet-Dry system hooked to the releaser along with 3, 1 inch single lines.  This is where vacuum distribution comes in and the math starts.

Line Allocation
Each pipe diameter has a cross section area
Knowing this will give you the cubic feet capacity per minute for the pipe.
It will also allow you to assign a percentage of a vacuum pipes capacity to each pipe.

Area of the Pipe

¾”        .44 sq. inches              1 ½”     1.77 sq. inches

1.0”     .78 sq. inches                2.0”       3.14 sq. inches

1 1/4″    .1.23 sq. inches            3.0”     7.07 sq. inches

How do I determined what percentage of my vacuum is going to each line?

Let’s say in your woods you have 4 lines, three 1″ lines with 1/3 of my taps on them and one 1 ¼” over 1″ Wet-Dry operating 2/3 of the taps. Here is a simple formula determine vacuum

For the 1 inch lines .78 + .78 + .78 = 2.34.  For the 1 ¼ inch line = 1.23
Doing the math, 2.34 + 1.23 = 3.57 sq. inches

.78 ÷ 3.57 = .218 or each 1 inch line receives 21.8 % of the CFMs.  All together the 1 inch lines in this system are receiving 65.4% CFMs.
That leaves the remaining 34.6% CFM capacity for the 1 1/4 line.

Now you have 2/3 of the taps on the 1 ¼” Wet-Dry line only receiving 1/3 of the CFMs. You need to redistribute the CFMs to the largest number of taps. To correct the problem, you need to reduce the number of CFMs going to the 3, 1″ lines or you need to increase the size of the dry line on the Wet-Dry system. If you apply the math using the above information you can obtain the most economical solution.

For instance, if you installed a 2″ line in place of the 1 ¼” this would apply 60% of the CFMs to that line and 40% to the 3, 1″ lines. You could also bring all 3, 1″ lines together into a vacuum booster with a 1 ¼” outlet going to the releaser. What you would end up with in the second scenario is two lines coming into the releaser of the same size, each with 50% of the CFMs. Remember the wet line does not count as a vacuum line; its only function is to transfer liquid. The only other considerations are to avoid line loss from the vacuum pump to the releaser by using a 2″ or 3″ line and to account for all the CFMs used by releasers and other equipment on the system.

Author: Les Ober, Geauga County OSU Extension

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