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Thread: Riser from air compressor manifold?

  1. #1

    Riser from air compressor manifold?

    I intend to connect 2 air compressors via a manifold to service my shop air. One single stage 5hp (single phase) compressor with a 60 gal. tank will be the primary source. The second compressor is 5hp (3 phase) with an 80 gal. tank and will only be used if more CFM is needed. The loop in the shop is 3/4" copper. I understand it's good practice to make the riser going to such a loop larger than normal to trap moisture by slowing down air velocity. I was planning to make the riser 1" but was wondering if it should be larger. Any formulas or guidance on sizing the riser?

  2. #2
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    I think you are over thinking it. Just plugging the other compressor into a drop with a double male connector will even work.

  3. #3
    Quote Originally Posted by Steve Rozmiarek View Post
    I think you are over thinking it. Just plugging the other compressor into a drop with a double male connector will even work.
    Probably but I would like to make the most of the installation and do it as correct as possible. After posting the question I found a couple of videos by Keith Rucker and Stan Zinkosky where they had similar installations. I don't plan to install driers or refrigerated coolers as Rucker did but I will bump up the riser size to something larger than 1" a short distance for the reason mentioned earlier.

  4. #4
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    Quote Originally Posted by Steve Mathews View Post
    Probably but I would like to make the most of the installation and do it as correct as possible. After posting the question I found a couple of videos by Keith Rucker and Stan Zinkosky where they had similar installations. I don't plan to install driers or refrigerated coolers as Rucker did but I will bump up the riser size to something larger than 1" a short distance for the reason mentioned earlier.
    When researching this long ago I found several independent but similar suggestions: make the condensing pipe fairly long (I remember a recommendation for 25') and slope it slightly to allow condensate to accumulate in a drip trap at the end before the riser to the loop. Drain the trap occasionally. The condensing pipe could be a serpentine with sloping horizontal sections. I don't remember reading about using an increased diameter for expansion cooling but it sounds plausible. I assume you are adding a dryer of some sort in the line. I use a water separator followed by a desiccant dryer.

  5. #5
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    Or run two 3/4 parallel pipes. I let you do the math of surface area/volume and speed of flow of varying diameters and number of pipes in parallel.
    Bill D.

  6. #6
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    My gut feeling is a much larger pipe would be more effective. Something on the order of a foot to a foot and half diameter, and 3 or 4 feet long. That kinda sounds like the tank on the compressor ;-) That's where the water comes out, more or less squeezed out by the increased air pressure like squeezing a sponge. Keep it drained. If you're getting water out of there, it's not because the flow is picking it up off the surface of the puddle. And I doubt a short section of slightly larger pipe is going to fix it.

    As for a pressure drop and or expansion cooling in a slightly larger pipe, it's probably unmeasurable unless the flow rate is extreme. At that kind of flow rate, I'd think any mist is going back into suspension once the pipe necks back down anyway.

    The sloped line sounds like a good idea to help catch whatever gets out of the tank. And if you're using that much air, maybe plumbing an extra vertical tank into the system would be better yet.

    As for the compressors, I'm wondering if the 3 phase unit might be more efficient electrically? Unless you're running it off a rotary converter?

  7. #7
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    Smaller pipes have a larger surface area to volume ratio. So multiple smaller pipes offer more cooling surface then one larger pipe. Look at an air conditioning condenser on a car. It is several parallel tubes bent into z shapes.
    Bill D

  8. #8
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    If you are hoping to stop condensate with the larger diameter riser, you need to also provide a condensate boot with drain to eliminate the condensate. Running saturated steam lines, the line suppling the riser went into a tee with extended condensate leg with trap. The line size was not increased for the riser section, but there seemed to always be some condensate collected since steam was saturated and some moisture forming in the line.

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