Tell me if this sounds familiar: You’re ready to go into testing with your design and the last step is the sealing requirement. You review the design guidelines, rules of thumb, and use the interactive calculators to find the perfect o-ring. Then, you check for its availability and it’s not in stock. Now tooling and molding will be required and the lead time will cause a missed deadline.
Choosing an o-ring is very similar to selecting nuts and bolts. Selecting a bolt with a custom thread and pitch should be the last resort. Instead a standard size should be considered to meet the application requirements and be readily available. The same philosophy applies to o-rings. So to avoid this predicament take advantage of Apple Rubber’s standard o-ring inventory.
The Society of Automotive Engineers designated AS568 as the o-ring standard. Dash numbers were assigned to specific sizes. For example, an o-ring with .739 ID X .070 C/S would be an AS568-018. For a full listing of AS568 sizes, go to download the AS568 PDF here. The important thing to note here is that these dash numbers/sizes are the standards. These sizes will be more readily available from an o-ring supplier. At Apple Rubber we carry various AS568 dash sizes, with multiple material and durometer selections in stock. The best odds to find an o-ring from stock are with an AS568 size.
Another advantage in considering AS568 sizes are the established groove dimensions. The gland design has already been done for you. All dimensions to properly accept AS568 sizes are charted. Static and dynamic groove dimensions for piston and rod orientation as well as axial seal groove dimensions are documented.
- Static axial seal gland dimensions
- Static radial seal gland dimensions
- Dynamic radial seal gland dimensions
So with maximum availability and competitive pricing, tested and proven groove dimensions, one should first consider an AS568 size for the sealing requirement.
Of course, AS568 sizes have their limitations as they do not encompass all o-ring sizes. This is where Apple maintains their competitive edge: INVENTORY. Apple has in stock o-rings that are above, below and in between the AS568 sizes. The last inventory count was over 12,000 sizes and material combinations. To find a range of sizes and materials that are in stock, go to our o-ring search. Please note that these sizes are not available in all materials and durometers.
Now let’s redo our scenario.
An o-ring from stock is selected with no tooling required and next day availability. It might not be the optimum size based on the calculations, but it is something close. O-rings will function even if design parameters are not at nominal. Contact us if the design parameters are just outside of the recommended guidelines, we will provide feedback so you know what to expect.
Even if the o-ring did not meet the application requirements, it is not a complete loss. Apple’s vast inventory gives you the advantage to test additional o-rings with variations in inner diameters, durometers and cross sections.
A data trend has been established.
Now there is data to support the fine tuning of a custom o-ring.
By steering the engineer to consider available sizes first, this minimizes the risk and cost to the rapid development process by having an o-ring to test the next day.
Seal it right, right from Apple.