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Old 09-21-2006, 01:23 AM   #1
poorfatjames
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Default Is the standard 3/8" tube refer to inner or outer diameter?

um...Is the standard 3/8" tube refer to inner or outer diameter?


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Old 09-21-2006, 03:08 AM   #2
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Typically the measurement of tubing is expressed as ID. In my trade as a refrigeration tech, refrigerant tubing is expressed as an OD.

John

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Old 09-21-2006, 03:32 AM   #3
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Will say on the tubbing. Oviously imporant.

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Old 09-21-2006, 05:22 AM   #4
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I discovered while shopping at Home Depot that they had tubing that specified the size both ways. I thought that was odd at the time, but thanks to John's explanation, now I know why. One box was labeled 1/2 inch tubing, and it was 1/2 inch ID, 5/8ths OD. Right next to it was another box labeled 1/2 inch tubing that was 3/8ths ID, 1/2 inch OD, The latter was called "refrigerant" tubing, as John said.

You can decide pretty easily what size you want regardless of what the box says when you're standing in the ailse at Home Depot. I do wish that retail vendors of manufactured chillers would specify whether they are talking about ID or OD in their product listings. Maybe some do. MoreBeer does not. I bought a 50 foot B3 Superchiller from MoreBeer that they advertise as a 1/2 inch chiller, but fail to mention whether that is ID or OD. They are being truthful. It is 1/2 inch, but it is the refrigerant specification, so that is 1/2 inch OD, not ID. I had also made myself a 25 foot chiller (now my pre-chiller) from I/2 inch tubing. But mine is 5/8ths OD.

I doubt it really matters that much, but because copper tubing is labeled differently depending on whether it is refrigerant tubing or not, people who sell products made from copper tubing really should indicate whether they are referring to ID or OD.

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Old 09-21-2006, 10:27 AM   #5
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Quote:
Originally Posted by beer4breakfast
I discovered while shopping at Home Depot that they had tubing that specified the size both ways.
Home Depot led me to my question. It seemed to make sense that they main reference would be to the ID, but the stuff I saw prioritized the OD.

Now that I've been made aware, I see that both my LHBS, DeFalco's in Houston, and Austin Home Brew specify the "standard" 3/8" tubing as 3/8" ID and 1/2" OD.

http://www.austinhomebrew.com/produc...93cb51aad95571
http://www.defalcos.com/Catalog_i296...l?catId=126679
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Old 09-21-2006, 10:55 AM   #6
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I also worked with tubing for over ten years and almost all of it was referenced by OD. Sometimes you'd see some by ID but, generally speaking, tubing was OD and pipe was ID. One reason for referencing tubing by OD is because compression fittings are sized to fit OVER the tubing... the OD is the critical dimension. Piping systems on the other hand, are usually more flow rate critical. Flow calculations are based on the ID size of the pipe therefore making ID the critical dimension.

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Last edited by Nate; 09-21-2006 at 11:01 AM.
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Old 09-21-2006, 11:16 AM   #7
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Quote:
Originally Posted by Nate
I also worked with tubing for over ten years and almost all of it was referenced by OD. Sometimes you'd see some by ID but, generally speaking, tubing was OD and pipe was ID. One reason for referencing tubing by OD is because compression fittings are sized to fit OVER the tubing... the OD is the critical dimension. Piping systems on the other hand, are usually more flow rate critical. Flow calculations are based on the ID size of the pipe therefore making ID the critical dimension.

Ok, interesting. When would flow rate _not_ be the most critical factor, though? When you focus on other things, like durability, cost, or longevity?

Oh, and that is one sweet brewery set up you have. My egg crate bows to your skills.
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Old 09-21-2006, 11:26 AM   #8
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Often tubing is used for smaller applications where flow rate per se is not that critical... instrumentation, sensing lines, small supply lines, etc. I'm definitely not saying that flow rate is not important just that it usually becomes more important in piping systems. As far as durability, cost, longevity, etc, you're usually looking more at material type and wall thickness properties. Speaking of wall thicknesses, this definitely comes into play more with piping and is another factor in sizing pipe by ID. The wall thicknesses vary while the ID of the pipe remains the same.

Thanks for the brewery comments by the way.

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Last edited by Nate; 09-21-2006 at 04:00 PM.
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