Dunno if this is the right place for this but...

[GirGirl]

Can anyone please tell me why Manhole covers are round?
i can't see how this could improve their function in any way...

Fanks in advance.

x

[Clanad]

Since they are round, they won't fall through the receptacle that holds them (being larger than the hole)...

[GirGirl]

Maybe I'm missing sumink or just being dim but...

Eh?

Couldn't you just do that with a square one?

x

[MargeB]

In the spirit of equality, can we please call them by their proper name: person hole covers.

;-)

Square one wouldn't work, me thinks.

If you think about the round one, no matter what way you hold it , its widest point is always larger than the hole into which it fits...so it doesn't fall through.

If you think about the square one, sure the sides are all shorter than the cover, but corner to corner diagonally is larger than the cover, and the cover will fall through.

 

[UmBongo]

the popular Stanton Warrior person/man hole ( :-) ) cover is rectangular.

[GirGirl]

People cover it is!

:)

Guess I'm just dim tho' as I still don't get it.

x

[Tim Baxter]

Take a square biscuit tin and lid, stand the lid on its edge, keep the lid upright and insert its bottom edge into the diagonal of the tin.  See now?

Rachael Heyhoe Flint called her box, "My manhole cover"!!!

Howzat?

[VINNY100_2]

The sewer cover just out side my house is square?

[smudge]

http://www.theanswerbank.co.uk/How-it-Works/Question94056.html

This might help.

[newtron]

You can make a square cover much bigger than the hole where it overlaps significantly onto the pavement.  This would prevent the cover from falling into its hole.

[MargeB]

Might not give you much hole though after much tugging to prise cover...

[outaboutnowt]

We have got triangular ones as well.

[MargeB]

Equilateral triangles?

[UmBongo]

makes sence to have a round one...

[JackRegan]

I thought it was round so you could drop the cover straight back on without haveing to line it up first like you would have to do with a square one.

[sddsddean]

Round ones are a tight fit (anyone apart from me ever been down a manhole?) Square ones are usually larger, so are normally used on larger sewers that need more maintanence. Triangular are usually hinged, so they lift like a tea pot lid and are even harder for you to get into. If you look at my comments in the link smudge gave, you will see that the usual reason for the shape is the clients whim.

[oligopoly]

Would i be right in thinking that due to their weight, the circular ones would be easier to move ie. roll it out of the way. Could this be another reason for the shape?

[sddsddean]

Not necessarily. You have grade A,B and C covers according to their predicted traffic loading. The more load, the heavier the cover. The usual problem is getting the bugqers to move at all, as they usually haven't been lifted for years!

[oligopoly]

Sorry reading my previous post, it seems i did not word it in the best possible way.

What i meant was whether the fact that round covers can be rolled in order to move them away from the hole could be a factor in deciding the shape.

I agree with the part that many have not been moved for ages though!

[tommy_g003]

Here's an interesting point: The shape of a fifty pence coin (UK) and a 20 pence coin (UK) would also work as manhole covers (though you might want to make them a bit bigger).

If you're not familiar with the shape of the coins, look here...
http://www.royalmint.com/RoyalMint/web/site/Corporate/Co rp_british_coinage/CoinDesign/50pCoin.asp

The shape is technically an 'equilateral curve', which means it has a consistent rolling diameter, so it has the same height at all times, if you roll it. This is useful for coin slots and vending machines etc. Each of the slightly curved sides is actually centred on the opposite corner of the coin, so you could draw your own with a compass if you really wanted.

You see, I told you it was interesting =)

- Tommy G

[woodys_cool]

at a guess, its to quickly tell what is under the cover! they dont seem to be evenly spaced out or anything so my guess is that when the county guy in his white van with 'water board' printed on the side is going through your town, hes looking for the shape that he knows is for water only, i dont know what that is tho, but i think this could explain the square, rectangle, triangle business.