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Thanks Dan, I saved that for
reference.
Kindest regards,
Bill Akins.
----- Original Message -----
Sent: Monday, June 06, 2005 11:36
PM
Subject: Re: [PSUBS-MAILIST]
O-rings
Stan,
Here's more then you want to know about O-rings
but there have been a few questions about O-rings lately and I got on a role
while typing. ;-)
For sealing water oil or air, Buna is just
fine. It's cheap, works fine and lasts a long time! It's not
really great for weather exposure but most seals see little weather when in
use anyway. When your dealing with chemicals, high heat of very
cold conditions there are better choices. Anything you'll be diving a
sub in is ok with Buna.
There are several manufactures of O-rings but a
Buna ring is a Buna ring, no matter who makes it. "Parker" http://www.parker.com/ead/cm2.asp?cmid=983 is
a very large manufacture and has some good information available for gland
size and the squeeze required for different applications, but so do other
manufactures of O-rings. Here's another company with good groove design
information. http://www.allorings.com/ You need
to chose the proper application type for the proper groove design and ring
size. There are static seal applications (pipe flanges and
gaskets). There are dynamic applications, sliding and rotary. Only use
O-rings for slow rotary applications. Lip seals and face seals are
better for rotary applications such as motor shafts but hand levers and hand
cranks are good rotary applications for O-rings. Also, consider weather
you want the ring to snap in a shaft groove or pop in a housing groove.
There are different diagrams to follow for selecting each application groove
and ring size.
O-rings can be purchased from just about any
bearing supplier. A distributor that handles ball bearings usually
handles bronze bearings, lip seals and O-rings. Another easy to use
source is "McMacter Carr" out of New Jersey. http://www.mcmaster.com/ Type
in O-rings and click FIND in the search they provide. They are
a major industrial supplier and handle almost any hardware, seals and
what-nots you'll need to build a sub. They are reliable and
fast. I order O-rings from .500 inch OD to 23 inch OD and get them
the next day UPS. The small ones come in packaged quantities but there
cheep and you'll have spares in case you rip one.
Keep in mind O-rings are stocked in standard
sizes. These sizes are referred to as standard "dash numbers."
Each ring is designated with a three digit dash number. You have to look
at a chart to find the number for the size you need. The dash number
tells the cross section, the first number, and the diameter of the ring,
the second and third number. Here's a chart. http://www.allorings.com/size_cross_reference_framed.htm When
ordering, you need to specify the material type also. A thicker cross
section O-ring is a better choice if you have the room for the larger gland it
requires. The thicker the ring the more forgiving the amount of squeeze
is and still get a good seal.
The clearance between the mating parts is a
factor also. If you have a big clearance between mating
parts your sealing, the O-ring seal can be squeezed out of its groove and
into the excessive clearance between a shaft and housing, by the pressure
your sealing. This type of failure is called extrusion and is more
common in hydraulics where pressures are in the 2000 to 5000 PSI
range. Most sub applications aren't nearly that high so extrusion of the
ring isn't much of a problem unless your sealing high pressure
air.
Hope this helps someone,
Dan H.
----- Original Message -----
Sent: Monday, June 06, 2005 7:26
PM
Subject: [PSUBS-MAILIST] O-rings
Can anyone explain to me the differences in )-ring
materials? I've heard of buna-N O-rings and nitrile O-rings, and I'm
sure there's more, but I don't have a clue what's best to use for
what...
What is a good source of information on O-ring construction, material,
use, installation, etc.?
Tanks! (haha)
Stan
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