O-Rings

Go Back to View Vedovell Products
Download PDF of O-Rings Specification Guide

The O-ring is the most widely used seal in the industry. It is easy to install, may be used as a double-acting seal and can seal pressures of up to800 PSI. With pressures over 800 to 2,000 PSI , backup ring(s) should be considered for higher pressures. The o-ring is typically used as reciprocating seals, not for rotating shaft applications. Lip seals should be used for rotating shafts.

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 O-rings

O-rings are specified by calling out the O-ring size, and the compound.

Size

O-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: "AS568-110."

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:
Fluid Compatibility Chart
Temperature Range Chart
General Elastomeric 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 "Durometer-Pressure-Gap Chart"
View Specification Reference Guide


GROOVE DESIGN CHART FOR O-RING INSTALLATION

A = Uniform Dash Number
B
= Actual Cross Section Dia.
C = Dynamic1
D = Static
E = Dynamic1 + .000/-.001
F = Static +.000/-.004
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 (Minimum)
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

[Top]

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

-001 thru -003
-013 thru -050
-117 thru -178
-223 thru -284
-350 thru -395
-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 groove 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:

Chart of O-Ring Groove Dimensions
Rod Seal
Given:
Rod Diameter C
O-ring Cross Section W
Dynamic application
No back-ups required

Example:
= .500"
= 3/32" nominal
Determine:
O-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
O-ring Cross Section W
Static application
No back-ups required

Example:
= 1.000"
= 1/8" nominal
Determine:
O-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"

[Top]


Copyright © 2012 R.J. Vedovell, Inc.
11128 James St. Zeeland, MI 49464, USA
800-782-2827 / 616-748-6900 phone • 800-477-9825 / 616-748-6969 fax