[modeleng] Re: O rings

The experts in our Hereford club advocate that an O ring should roll 
when in contact with a sliding surface. You have the make the groove 
large enough, so that the ring is not gripped. The groove should have a 
slightly bevelled edge as the ring wil try to leave the groove and you 
don't want to damage it. The ring should be slightly compressed, but 
not enough to trap it in the groove. The theory seems to be sound for 
water pumps and the like.

Andy

>----Original Message----
>From: clif.gwr@xxxxxxxxxxxx
>Date: 21/11/2008 10:58 
>To: <modeleng@xxxxxxxxxxxxx>
>Subj: [modeleng] Re: O rings
>
>Hi All,
>
>I tend to use Viton O rings for steam and sliding joints, the only 
snag 
>being that untill I read Craig's e-mail I did not realise that there 
were 
>different types so perhaps I have been lucky.
> Long before Martin Evans started specifing O rings for the steam 
pipe 
>joints at the front tube plate I had worked out that it was far 
easier to 
>make a compression joint using O rings than all the fun and games of 
trying 
>to screw a bush onto the steam pipe from the regulator while at the 
same 
>time screwing the bush into the front tube plate and get it all steam 
tight. 
>I also make compression joints for the steam and exhaust connections 
to the 
>steam chests.
>I have never used Silicone O rings for sliding joints,despite the 
fact that 
>ME suppliers recommend them owing to the fact that the O ring 
manufacturers 
>say that Silicone cannot mechanical wear. Any comment please Craig?
>
>Regards
>
>Clif
>
>
>
>----- Original Message ----- 
>From: "Craig Gluyas" <craig@xxxxxxxxxxxxxxx>
>To: <modeleng@xxxxxxxxxxxxx>
>Sent: Friday, November 21, 2008 10:08 AM
>Subject: [modeleng] Re: O rings
>
>
>> As a former seal specialist for a valve manufacturer, i guess this 
is my
>> area!
>>
>> O-rings are very suited to our uses, we just have to be careful 
what
>> material to use. Silicone is about the best & most widely suitable 
for -15
>> to 200'C. Other materials vary, even to within blends. For example 
Viton A
>> is not recommended for use with steam where as Viton B or Viton GF 
is.
>> Viton is good for about the same temperatures as Silicone.
>>
>> Other seals such as EPDM and Nitrile are readily available, but are 
less
>> tolerant to chemicals (Natural Rubber does not like Oils for 
example)
>>
>> An excellent compatibility website used in the industry is 
available here
>> http://www.coleparmer.com/techinfo/ChemComp.asp
>>
>>
>> Hope that helps!
>>
>> Craig
>>
>>
>>
>>> There is a discussion on a message board about the use of O rings 
in 
>>> model
>>> steam engines.
>>> Both the types and where they are, or are not, suitable, together 
with 
>>> the
>>> advantages /disadvantages of them compared to other forms of seal.
>>>
>>> What opinions do members here have?
>>>
>>> Alan
>>>
>>>
>>>
>>> MODEL ENGINEERING DISCUSSION LIST.
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>>
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>
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