# Why Do Long Steam Pipes Often Have a U-Shaped Section?

1. Oct 12, 2011

### JSGandora

1. The problem statement, all variables and given/known data
Long steam pipes often have a section in the shape of a $\bigcup$. Why?

2. Relevant equations
None.

3. The attempt at a solution
I'm at a loss. It might be because of some sort of volume expansion, but I'm not entirely sure why...

2. Oct 12, 2011

### DaveC426913

What does steam do if left alone long enough, say passing through a long pipe?
What might this steam-that's-left-alone-long-enough do differently in the U-shaped section of pipe that it might not do in the long straight section?

3. Oct 12, 2011

### JSGandora

The steam will condensate if left alone long enough but when it's in a U-shaped section, it would rise. I don't know what's next.

4. Oct 12, 2011

### DaveC426913

What do imagine this U-shaped section looks like? Describe it.

5. Oct 12, 2011

### JSGandora

Um, probably a vertical "bump" in the pipe, like this:

6. Oct 12, 2011

### DaveC426913

Ah. An upside down U. Sorry. I assumed it was a right side up U.

I led you down the wrong path then. Apologies.

You were closer to the mark with your guess. But it is not volume expansion. Ever walked a large bridge? Ever notice the bridge is cut into sections, with with rubber sandwiched between them?

7. Oct 12, 2011

### JSGandora

Ohhh, I think it's for allowing expansion so there's not that much stress because when expanding with the U-shaped curve then the pipe would get closer together across the empty space between the ends of the curve. Thank you so much! What would be the purpose of an right-side up U then? I would imagine that it's the same but from what you said it seems it does not serve the same purpose.

8. Oct 12, 2011

### DaveC426913

In a pipe that passes steam (such as my dryer vent), you would want a section that is lower than any other part of the pipe, with a drainage valve at that point for condensation.