FSR: O-Rings 1

O-Rings

The o-ring is the most widely used seal in industry. It is easy to install, can be used as a double-acting seal, can seal pressures to over 5,000 psi in static and dynamic applications and is very economical.

While simple in concept, the o-ring can be sophisticated in application. The information in this catalog is intended to give a brief overview of o-ring design and selection.

Specifying 0-Rings
0-rings are specified by calling out the o-ring size, and the compound.

Size
0-rings are available in 349 sizes as set up by the Aerospace Standard 568 published by the Society of Automotive Engineers. These sizes are designated by dash numbers as shown on the 568 DASH Chart. For instance, an o-ring with an inside diameter (I.D.) of .362 + .007" and a cross section (W) of .103 + .005 is designated as: "AS568-1IO."

Compound Selection
Compounds are available in a variety of elastomers such as Nitrile, Neoprene, Ethylene Propylene, Fluoroelastomer, etc. To select the proper elastomer, check the following in Properties:

For o-ring sizes other than standard sizes, specify the actual dimensions desired for the inside diameter (I.D.) and the cross section (W). There may be a tooling charge for such non-standards.

Usually you will be able to find one best base elastomer to meet these requirements. The next step is to determine the durometer (hardness) needed, from the "DurometerIPSIlGap Chart" (see Properties section).

Groove Design Chart For O-Ring Installation

A = Uniform Dash Number
B= Actual Cross Section Dia.
C = Dynamic¹D = Static E = Dynamic¹ + .000/-.001
F = Static +.000/-.001
G = No Backup Ring
H = One Backup Ring I = Two Backup Rings
J = 500 PSI
K = 1500 PSI
L = Eccentricity³ (Maximum)
M = Radius (R)

Diametral
Squeeze (Minimun) Gland Depth F Groove Width G + .003 Diametral² Clearance (Max) D

See
A
above See
B
above See
C
above See
D
above See
E
above See
F
above See
G
above See
H
above See
I
above See
J
above See
K
above See
L
above See
M
above

-001 .040+.003 .004 .006 .033 .031 .056 - - .005 .0025 .002 .010

-002 .050 +.003 .005 .008 .042 .039 .070 - - .006 .003 .002 .010

-003 .060 +.003 .006 .009 .051 .048 .084 - - .007 .0035 .002 .016

-004thru-050 .070 +.003 .007 .011 .060 .056 .098 .140 .207 .008 .004 .002 .016

-102thru-178 .103 +.003 .010 .015 .090 .085 .144 .173 .240 .009 .004 .002 .016

-201thru-284 .139 +.004 .014 .021 .121 .114 .195 .210 .277 .010 .006 .003 .031

-309thru-395 .210 +.005 .021 .032 .184 .173 .294 .313 .412 .011 .007 .004 .031

-425thru-475 .275 +.006 .028 .042 .241 .227 .385 .410 .540 .012 .008 .005 .047

1. The following sizes are not normally recommended for dynamic service, although special applications may permit their use:

-001 thru -003 -223 thru -284

-013 thru -050 -350 thru -395

-1 17 thru -1 78 -461 thru -475

2. Clearances shown are based on 70 durometer materials. The clearances must be held to an absolute minimum consistent with design requirements for temperature variations and should not exceed the values shown.

3. Total indicator reading between cfroove and adjacent bearing surface. All surfaces and corners must be free of tool marks and scratches.

Surface Finishes For O-Ring Installation

Type Possible Result Comments

Polished (non-porous) Lubrication will be lost resulting in high friction rate and possible seal failure. Not recommended

Rough Tearing and abrasion of seal may occur, possible seal failure. Not recommended

Burnished/Mandrel A surface finish exceeding the recommended surface finish range, possible seal failure. Although these methods produce a very accurate diameter, they are not recommended.

Ideal 20-24 RMS (,5-.6 Bar)
20-32 RMS (.5-.81 Bar)
Not to be finer than 1 6 RMS (.4 Bar) Recommended

Groove Design For O-Ring Installation
O-ring groove dimensions may be calculated as follows:

Rod Seal
Given:
Rod Diameter C
0-ring Cross Section W
Dynamic application
No back-ups required Example:
= .500"
= 3/32" nominal

Determine:
0-ring size
Gland Depth F
Groove Width G
Rod Gland D Example:
= AS-568-112 (1/2" ID x 3/32" W nominal dimensions)
= .090 .003(from chart, page 2)
= .144 ± .003" (from chart, page 2)
= C + 2F = .500" + 2x.090"= .680"

Piston Seal
Given:
Cylinder Bore A
0-ring Cross Section W
Static application
No back-ups required Example:
= 1.000"
= 1/8" nominal

Determine:
0-ring size
Gland Depth F
Piston Groove B
Example:
= AS 568-210 (1" OD x 1/8" W nominal dimensions)
= .1 14 (from chart, page 2)
Groove Width C = .195 + .003" (from chart, page 2)
= A-2F = 1.000" -2x. 1 14"
= .772"

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