Pvc expansion fittings

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crtemp

crtemp

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Wa state
I see 352.44 talks about the use of expansion fittings. Would a 90 degree fitting be considered an "elbow" if the 90 is strapped to the wall?
 
A 90 degree bend in the run of pipe could serve to accommodate expansion, but only if the bend and the pipe close to it are not fastened down in a way that would restrict movement in response to expansion or contraction of the long run.

For example, if two long runs meet at a 90 degree bend this would only take care of expansion if the bend I'd free to move diagonally. Which is hard to do with conventional supports.

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jumper said:
Are you saying you have a 90 degree expansion fitting?

Never heard of one.

I think I am unclear on just exactly what you are asking.
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They are just regular 2' pre made 90 degree fittings. There is 21' of straight pipe in between them.
 
jumper said:
And both are strapped to a wall?

Does not really matter I think, 21' of pipe is not going to expand or contract in any significant amount, less than a 1/4" unless you have some super wild difference in temps.
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It's strapped at least 1' from the 90's in both directions. I would think the temp swing couldn't be over 100 degrees. Never colder than 20 here and not more than 100 either. It's under the eve of a roof but I still don't believe it would be over 120 degrees at the most.
 
I think the OP is asking if an 90 degree bend is considered an elbow as used in the context of 352.44 for securely mounted items. Yes, back-to-back 90's would require an expansion fitting where the run between the fittings will develop a 1/4 inch or more expansion.
 
RB1 said:
I think the OP is asking if an 90 degree bend is considered an elbow as used in the context of 352.44 for securely mounted items. Yes, back-to-back 90's would require an expansion fitting where the run between the fittings will develop a 1/4 inch or more expansion.
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That was sort of what I was getting at. According to the expansion chart I'm allowed about 25' of pipe before I'm required to use the expansion fitting. I only have 21' of pipe in between the 90's but the entire length of the conduit run is about 37'. So as long as the 90's count at relief points I'm good
 
crtemp said:
That was sort of what I was getting at. According to the expansion chart I'm allowed about 25' of pipe before I'm required to use the expansion fitting. I only have 21' of pipe in between the 90's but the entire length of the conduit run is about 37'. So as long as the 90's count at relief points I'm good
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If you have 100-125 degree temp change you should need expansion fitting on much shorter run of pipe then 25'

A 100F temp change results in 4.06" of pipe length change according to the table, that would be .406" length change for 10 feet - still need expansion fitting on a 10 foot run. A 1/4 inch change in length at that temperature range should occur in around 74 inches of raceway according to my calculations.

Is possible you only need an expansion fitting every 25 feet of run, but need at least one for a 74 inch run.
 
kwired said:
If you have 100-125 degree temp change you should need expansion fitting on much shorter run of pipe then 25'

A 100F temp change results in 4.06" of pipe length change according to the table, that would be .406" length change for 10 feet - still need expansion fitting on a 10 foot run. A 1/4 inch change in length at that temperature range should occur in around 74 inches of raceway according to my calculations.

Is possible you only need an expansion fitting every 25 feet of run, but need at least one for a 74 inch run.
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I guess I did my math wrong
 
crtemp said:
I guess I did my math wrong
Click to expand...

Hold on a sec. Did you take into consideration the ambient temp of when the pipe is going to be installed?

The temp differential is the difference between install temp and max hot or cold, whichever is greater,.

You said min is 20F and max is 100F, add 30F to max if in direct sunlight.

If install temp that day is 70F then min difference is 70F-20F=50F and max difference is at worst 130F-70F=50F.

Your temp difference would be 50F, not 100F. You only get a temp difference swing of ~100F if you install on a day that is max or min temp that day.
 
jumper said:
Hold on a sec. Did you take into consideration the ambient temp of when the pipe is going to be installed?

The temp differential is the difference between install temp and max hot or cold, whichever is greater,.

You said min is 20F and max is 100F, add 30F to max if in direct sunlight.

If install temp that day is 70F then min difference is 70F-20F=50F and max difference is at worst 130F-70F=50F.

Your temp difference would be 50F, not 100F. You only get a temp difference swing of ~100F if you install on a day that is max or min temp that day.
Click to expand...

I installed at 60 degrees. The pipe will never be in direct sunlight so I'm good there. Thank you for the added info.
 
jumper said:
Hold on a sec. Did you take into consideration the ambient temp of when the pipe is going to be installed?

The temp differential is the difference between install temp and max hot or cold, whichever is greater,.

You said min is 20F and max is 100F, add 30F to max if in direct sunlight.

If install temp that day is 70F then min difference is 70F-20F=50F and max difference is at worst 130F-70F=50F.

Your temp difference would be 50F, not 100F. You only get a temp difference swing of ~100F if you install on a day that is max or min temp that day.
Click to expand...

jumper said:
So your max temp differential is 40F either way. Use that for calculation and see what you get.

Post if you do the math, I am too lazy to do it right now.:)
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That will give you contraction and expansion numbers, but the installation must still be able to handle the total swing.
 
jumper said:
Hold on a sec. Did you take into consideration the ambient temp of when the pipe is going to be installed?

The temp differential is the difference between install temp and max hot or cold, whichever is greater,.

You said min is 20F and max is 100F, add 30F to max if in direct sunlight.

If install temp that day is 70F then min difference is 70F-20F=50F and max difference is at worst 130F-70F=50F.

Your temp difference would be 50F, not 100F. You only get a temp difference swing of ~100F if you install on a day that is max or min temp that day.
Click to expand...

The pipe is still subject to the full change from min to max temp, you just may want to compensate on how far to insert the non fixed piece into the expansion coupling depending on temp at installation time. If you have a fitting that allows for two inches of expansion and only have 1/2 inch of calculated movement, you don't have to watch as closely where you assemble it as if you have 1-3/4 inch of movement calculated.
 
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