Pressure Drop and its Relationship to Compressed Air

“Nothing happens until something moves.”
-Albert Einstein

OK; that’s how I started last week’s blog on stuff happening when heat moves (or, more accurately, is transferred.)  This week, it’s going to apply to pressure, and the movement (and/or lack thereof) of air in a pressurized system.  There are two primary reasons why a discussion of this is important in the context of the use of compressed air products:

The first reason is about ensuring sufficient air flow to get the job done:  As compressed air flows (or moves) through the system, it encounters friction with the inside wall of the line, be it pipe, tube, hose, etc.  Several factors affect this – the diameter and length of the line, the number of directional changes (think elbows,) and the finish surface of the inside wall.  The most important of these is the diameter…hopefully, the original plumbing layout didn’t use any more twists & turns than necessary, and no matter how hard you try, you’ll never polish the inside of a 1″ pipe enough to allow the same air flow as a 2″ pipe.  The length, as they say, “is what it is.”  Unless you can move your air compressor closer to the point(s) of usage (or the points of usage closer to your air compressor,) there’s not much you can do about this…unless, of course, you want to consider intermediate storage.

Let’s assume that your supply side, i.e., your compressor and main header(s), are adequately sized.  The usual pressure drop challenge, as it relates to sufficient air flow, is the air line from the header, to the product.  Put simply, the longer this has to be, the larger (in diameter) it’s going to have to be.  Here’s a video that demonstrates the performance changes that come with different length (and diameter) supply lines:

The second reason has to do with where a pressure drop occurs, relative to the point of use.  Common sense dictates the more energy you get to the point of use, the better & more efficient the use of that energy will be.  The potential energy of compressed air is no exception.  Consider these two blow off methods:

They may be loud, but they sure are inefficient…

With open end blow offs, like the copper tubing and modular hose shown above, the pressure drop occurs upstream, in the supply line itself…if you were to measure the pressure at the copper tubes’ manifold (left) or at any point in the modular hose (right,) it’s not going to be very high…it’s all being vented to atmospheric pressure through the open ends.  Depending on the size, and quantity, of the discharge holes, the pressure may build up a little, but if it gets too high, it’ll blow that modular hose apart…it’s not made to withstand any significant pressure.

Engineered solutions (like EXAIR Intelligent Compressed Air Products) are the efficient, quiet, and safe choice.

Engineered blow off devices, on the other hand, keep the air compressed right up to point of discharge, keeping the pressure drop (e.g., energy transfer) close to the point of use, for maximum efficiency.

If you’d like to find out more about optimizing your compressed air system for efficiency, performance, noise reduction and safety, give me a call.

Russ Bowman
Application Engineer
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