Question for the mathemagicians

ratio

Ok, I'm looking into the circle-in-circle problem (for sizing sleeves for linesets). It seems that it's basically an open ended problem, but I'm wondering if the limits of my application will make it solvable. What I want to know is something like the minimum % fill of a circle that will allow my linsets to fit. As an example, I have three copper lines (two 1-1/8" & one 3/4" with 1" insulation around each, so 2x dia 3-1/8" & 1x 2-3/4" ) and one raceway for control wires, c. 1" OD. What is the approximate minimum % fill that will allow them to enter the sleeve without interfering with each other? That's the maximum number of pipes that I'm interested in, but they are various sizes, generally 1 or 2 big, and 1 or 2 smaller.

Would I be better served by looking at this as a diameter problem, vs an area problem? The application is an Excel workbook, so I can easily math it, once I figure out exactly what I want to math.

Zman

I am not sure it is a percentage problem as much as a what will fit problem. A bucket of rocks with random sizes will weigh more than one with all the same sized rocks. Random sizes fit together better and fill all the little gaps. I would approach this graphically. Make a bunch of circles and see how they fit together in different size raceways.

ChrisJ

ratio said:

Ok, I'm looking into the circle-in-circle problem (for sizing sleeves for linesets). It seems that it's basically an open ended problem, but I'm wondering if the limits of my application will make it solvable. What I want to know is something like the minimum % fill of a circle that will allow my linsets to fit. As an example, I have three copper lines (two 1-1/8" & one 3/4" with 1" insulation around each, so 2x dia 3-1/8" & 1x 2-3/4" ) and one raceway for control wires, c. 1" OD. What is the approximate minimum % fill that will allow them to enter the sleeve without interfering with each other? That's the maximum number of pipes that I'm interested in, but they are various sizes, generally 1 or 2 big, and 1 or 2 smaller.

Would I be better served by looking at this as a diameter problem, vs an area problem? The application is an Excel workbook, so I can easily math it, once I figure out exactly what I want to math.

I can easily put all of these in Autocad and mess around but you gotta give me the actual OD of each one and the ID of the sleeve. I'm too lazy to figure it out.

At least I'm being honest....

hot_rod

What the number crunching will show and what is actually do-able may vary. I have tried putting pex in pex , and multiple pex in sleeves for underground piping to outdoor boilers. After a certain distance it is tough to push. Unless all the tube and insulation was laser straight.

Zman

hot_rod said:

What the number crunching will show and what is actually do-able may vary. I have tried putting pex in pex , and multiple pex in sleeves for underground piping to outdoor boilers. After a certain distance it is tough to push. Unless all the tube and insulation was laser straight.

Absolutely true. If the distance is significant or there are turns, that will be a game changer. If this is anything more than a short straight run, I would consult a commercial electrician. They have tons of experience with "what will fit" vs "what you can actually pull"

KC_Jones

As @ChrisJ said this can easily be done in CAD with given OD's. I have done this more times than I can count. My experience, if CAD shows it will work, it's going to be too tight. I have had very good luck doing it this way, then subtracting 1 circle/lineset/wire from the layout. So if 3 fit, 2 will work, if 4 fit, 3 will work. It's not scientific, but its worked well for me.

It's the friction of pulling things through that is the problem. Oh and pulling is always better than pushing, doing both is the best.

ChrisJ

KC_Jones said:

As @ChrisJ said this can easily be done in CAD with given OD's. I have done this more times than I can count. My experience, if CAD shows it will work, it's going to be too tight. I have had very good luck doing it this way, then subtracting 1 circle/lineset/wire from the layout. So if 3 fit, 2 will work, if 4 fit, 3 will work. It's not scientific, but its worked well for me.

It's the friction of pulling things through that is the problem. Oh and pulling is always better than pushing, doing both is the best.

I was going to post a picture to give an idea of what's what.

Zman

ChrisJ

Zman said:

PerryHolzman

There is no actual pure mathematical solution to putting multiple and different sized tubes into another tube. Too many variables. You are best to map it out with a cad program.

However, the other general advice is that unless you have perfect tubes of pipes, that you likely cannot put in something larger than 75% fill factor into a conduit (unless its very short), even with pulling lubricants (Does electrical wire pulling lubricants degrade pex and other plumbing tubing? I don't know.) That's a 75% fill factor for a single cable into a single conduit. Multiple cables I'd likely drop that to 60% to be able it works.

I note that for an example of the best that can be done is that eddy current inspection of tubing (round to within 0.002") can rarely use anything more than a 90% fill factor probe (round within 0.001") down a 5 - 60 ft tube in a heat exchanger. 80-85% is commonly used.

Should your conduit not be very round (say your using some form of large pex that was coiled and is thus oval...) you would need to drop it more.

I hope that helps,

Perry

ratio

Thanks, everyone. I'm familiar with the electrical side of things, spent a decade or so in that trade. I know about conduit fill. I was hoping for a generic solution , i.e. a percent fill I could plug in to a spreadsheet to help size the sleeve. What I've got going on is six underground (Yeah, don't get me started) sleeves to pull in the lineset for some VRF systems. Length is 20-30'. The largest set is what I mentioned above. The engineer called for 6", but the fill as calculated by me ranges from 65 to 83%—a far cry from the NECs fill of 40% for more than two conductors in a raceway.

I know that it could be modeled in AutoCAD, in fact we've got an AutoCad guy (and that'll probably be what we send to the engineer, so he'll be able to understand, <sigh>), but I'm trying to make a tool that I'll be able to use later on.

GW

Years ago we did a ductless install with one head in the detached garage. I had the builder drop 2” pvc with long sweep 90s (the very long sweeps, don’t know the jargon).

Well it was tight. We could pull across the horizontal but “coming back up” wasn’t happening.

We pulled it all back out and I ran a random. 3/8” ref line through the conduit. Attached to ref set. Plus we taped the entire set to reduce diameter. Repeated process. When we got to the hard part, I used a 8’ 2x4 as leverage and pried/leveraged the pull copper out in 6” or so pulls. (Screwed scabs to the wall in the garage as a “ladder”). I kept “wrapping” the pull tube around the 2x4. It worked.

ratio

That's about my plan, except that I hope to use Sparky's tugger to pull them in. & Hopefully use (& charge for) 8" PVC sleeves. Sparky's generously offered to dig the trench, since he's got to get power to them anyway.

& sweep 90 is the correct term! IIRC a 6" sweep 90 is 5-6' tall. I can't imagine how tall an 8" 90 will be.

hot_rod

Another option for an easy pull is two 45 ells maybe a foot or so in between. That may keep the depth of the trench down a bit compared to a long sweep.

I think two 45s with some distance between them pull easier, personally.

Bevel the inside of any pipe so you don't have a catch point if the pipe doesn't go into the fitting all the way.

GW

1 1/8” best of luck. How many feet you pulling? You’re gonna do “more than one big line” in the same pull? Wow that’s brave

Even with one 1 1/8 set you’ll need some leverage for sure. You not gonna use the basic armaflex line set stuff are you?

ratio

Two 1-¹/₈" (suction & hot gas), one ³/₄" (liquid), & one ³/₄" smurf tube for the controls for the worst of the pulls. Average length (6 units!) is going to be around 20'. Oh, & 1" insulation on all three pipes. I'm not afraid of the pull itself, but I'm worried that even 8" might not be big enough. I'll chain 'em on to the rope & tape up the first 3-4', hopefully that'll keep from shredding the itchy.

I've watched the beer guy pull in his lines to the tap. He uses talc as lube. If I can keep the inside of the pipe dry, I'll do that too.

mattmia2

So there is a shortcut of 40% fill (nec) or 30% fill (infocomm/bicsi) or 30% with only 2 conductors to prevent tangling that is genreally used in simple installations and 2 or 4 90's (again NEC vs bicsi). There is a more complex engineering method that can calculate the pulling force need to pull a bundle of conductors through a conduit. I don't know what that method is, but looking for that will likely get you your answer.

mattmia2

You will want to lubricate the insulation with something, it will stick and grab on the tubing if not. Also use electrical conduit and fittings, it is designed to keep the cabling protected from the cut edges of the tube. You might be able to get an electrician to bend a really long sweep in to it, there is tooling to heat it and bend it but someone that has a heating rig that large may be very limited. Could also order some pre-bent 90's from a supply house that has the right tooling to make them up.

Alan (California Radiant) Forbes

Oh, that would be such an exciting video to watch! All that pulling and effort by big men.
(It doesn't take much to get me excited these days.)

ChrisJ

Alan (California Radiant) Forbes said:

Oh, that would be such an exciting video to watch! All that pulling and effort by big men.
(It doesn't take much to get me excited these days.)

They make equipment to do the pulling for you.
No need for...........big men.

Solid_Fuel_Man

It always seems like it's the straight after the 90 where stuff gets hung up. The copper wants to continue to curl after the 90 and doesnt like going straight again.

Alan Welch

If possible it seems like it might be easier to prefab it by pulling through the straight pipe first, then sliding on and securing the risers and lowering it into the trench.

mattmia2

If it isn't possible to pull it through the conduit, it kind of defeats the purpose of the conduit.