# sewer access holes

ddebened
Posers and Puzzles 19 Nov '03 19:35
1. 19 Nov '03 19:35
Have you ever wondered why sewer access holes (aka man-holes) are normally round (at least in the United States)? After all, if they were square it might be easier for the workers to load their gear in and out. There is at least one good reason however, that they are round. And bonus points if you can come up with another shape that meets the same objective...
2. skeeter
515 + 30 days
19 Nov '03 21:14
Originally posted by ddebened
Have you ever wondered why sewer access holes (aka man-holes) are normally round (at least in the United States)? After all, if they were square it might be easier for the workers to load their gear in and out. There is at least one good reason however, that they are round. And bonus points if you can come up with another shape that meets the same objective...
Hmmm...I suspect the reason man-hole covers are round ( not very PC I know) is that they cannot fall through the opening. Is the other shape octagonal or hexagonal, pentagonal or ****gonal?

skeeter
3. 19 Nov '03 21:28
Originally posted by skeeter
Hmmm...I suspect the reason man-hole covers are round ( not very PC I know) is that they cannot fall through the opening. Is the other shape octagonal or hexagonal, pentagonal or ****gonal?

skeeter
I would vote for an equilateral triangle or a pentagon - I think shapes with two parallel sides such as squares and hexagons will generally let the lid fall through.
4. 20 Nov '03 03:00
Correct on the reason for round. Now as to alternate shapes:

I don't think equilateral triangle works because the height is significantly less than the length of a side. Thus the cover could fall through if you held it against one of the sides. It does not work because there is a short &quot;diameter&quot; (the height) that is less than a longer &quot;diameter&quot; (the side). The circle has a constant diameter.

Not sure about pentagon, but it stands to reason that as you add sides to a &quot;n sided&quot; shape it approaches a circle so it becomes harder to pass through. I think the width of the lip would influence how far you had to go in that progression.

The alternate shape I was thinking of is like an equilateral triangle except that instead of straight sides it has sides that are bowed out (remember the wankle engine? http://www.rotaryengineillustrated.com/)
I believe this shape is known as a Rouleaux triangle. Like a circle it has constant &quot;diameter&quot;.

5. 20 Nov '03 03:04
PS. In researching this I found a web site that claims that &quot;man holes&quot; in Britain are triangular. Can anyone confirm or deny that?

6. 20 Nov '03 19:21
Originally posted by ddebened
PS. In researching this I found a web site that claims that "man holes" in Britain are triangular. Can anyone confirm or deny that?

Ah - thanks for that answer, the Reuleaux triangle also defines the shape of a drillbit that can drill square holes.
( http://upper.us.edu/faculty/smith/reuleaux.htm )
I've not seen triangular manholes in Britain, but I have seen rectangular (and circular) ones.
7. 20 Nov '03 20:00
Originally posted by iamatiger
Ah - thanks for that answer, the Reuleaux triangle also defines the shape of a drillbit that can drill square holes.
( http://upper.us.edu/faculty/smith/reuleaux.htm )
I've not seen triangular manholes in Britain, but I have seen rectangular (and circular) ones.
And thank YOU for the correct spelling of Reuleaux triangle. I am interested in learning more about this, and I was wondering why there were so few search results at google (I was using a wrong spelling)...ðŸ˜›
8. 21 Nov '03 00:34
Originally posted by ddebened
The alternate shape I was thinking of is like an equilateral triangle except that instead of straight sides it has sides that are bowed out (remember the wankle engine? http://www.rotaryengineillustrated.com/)
I believe this shape is known as a Rouleaux triangle. Like a circle it has constant "diameter".
Thanks for that link, ddebened. I always wondered how a rotary engine worked exactly. Great, informative site!

I wonder why these engines are used more frequently.
9. 21 Nov '03 13:44
manholes are square in england do not know why maybe we english like to be square
10. 21 Nov '03 19:38
Originally posted by stoker
manholes are square in england do not know why maybe we english like to be square
I guess you have a lot of manhole cover accidents
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