When you need a custom O-ring, getting from “we need a seal” to an accurate quote can be surprisingly complex. An O-ring may look like one of the simplest components in an assembly, but its performance depends on much more than inside diameter and thickness.

Material, durometer, operating temperature, chemical exposure, pressure, tolerances and even the way the O-ring moves within an assembly can affect how it should be manufactured.

Providing the right information at the beginning of a project can help your custom O-ring manufacturer identify the appropriate solution, quote the job accurately and avoid unnecessary delays.

So, what should you know before requesting a quote for custom O-rings?

1. What Size O-Ring Do You Need?

Dimensions are the natural starting point.

O-rings are typically defined by their inside diameter (ID) and cross-sectional diameter. Depending on the application, however, additional dimensional information and tolerances may be important.

If you're replacing an existing O-ring, don't assume that measuring an old seal will always reveal its original dimensions. Elastomers can stretch, shrink, swell, flatten or otherwise change after extended service.

Whenever possible, provide an existing drawing or specification rather than relying exclusively on measurements taken from a used part.

If no drawing exists, additional information about the mating components or groove may help determine the correct dimensions.

2. Do You Have a Drawing, Part Number or Physical Sample?

You don't necessarily need a perfect engineering drawing before contacting a custom O-ring manufacturer.

If one is available, however, send it.

A drawing can communicate dimensions, tolerances, material requirements and other specifications much more clearly than a written description.

For replacement components, you may also have an OEM part number, historical purchasing information or a physical sample. Even incomplete information can provide a useful starting point.

This is especially important when sourcing custom O-rings for older machinery and equipment where the original seal may be discontinued or difficult to obtain.

3. What Material Does the Application Require?

Selecting an elastomer isn't simply a matter of choosing the material with the highest performance specifications. The material needs to match the actual environment in which the O-ring will operate.

Depending on the application, custom O-rings may be manufactured from elastomers such as nitrile (Buna-N), EPDM, silicone, neoprene, FKM and other compounds.

Each offers different characteristics.

Some applications require resistance to oils and fuels. Others need weather, ozone, chemical or high-temperature resistance. Still others require flexibility across a wide temperature range.

The best material is therefore the one suited to the combination of conditions the seal will encounter.

If you don't know which material you need, describe the application rather than guessing. An experienced gasket and sealing manufacturer can use that information to help identify appropriate material options.

4. What Will the O-Ring Come Into Contact With?

Chemical compatibility can make or break an O-ring application.

Tell your manufacturer about the substances the seal will encounter during normal operation. That might include oils, fuels, water, steam, hydraulic fluids, cleaning chemicals, solvents or process chemicals.

Don't overlook occasional exposure, either.

For example, a seal might perform perfectly with the material flowing through a system but deteriorate when equipment is periodically cleaned with an incompatible chemical.

An elastomer exposed to an unsuitable substance can swell, soften, harden, crack or lose its sealing properties. Providing complete exposure information during the quoting process can help prevent a material mismatch.

5. What Is the Operating Temperature?

Provide both the expected normal operating temperature and the anticipated minimum and maximum temperatures whenever possible.

A seal that performs well at room temperature may behave very differently after repeated exposure to high heat or extreme cold.

Temperature can affect elasticity, hardness, compression set and long-term material performance. It can also magnify the effects of chemical exposure.

For applications involving substantial temperature swings, don't simply provide an average. The extremes matter.

6. What Pressure Will the Seal Experience?

Pressure is another important piece of the application.

Tell your O-ring manufacturer the normal operating pressure as well as any expected peaks, spikes or unusual conditions.

High-pressure applications can create different sealing challenges than low-pressure or static applications. Depending on the design, excessive pressure can contribute to extrusion or other forms of seal failure.

Understanding the pressure environment helps provide a more complete picture of what the custom O-ring will be expected to withstand.

7. Is the Application Static or Dynamic?

Not every O-ring simply sits between two stationary surfaces.

A static seal is used between surfaces that remain essentially stationary relative to one another. A dynamic seal operates where movement occurs, such as reciprocating or rotating components.

That distinction matters.

Dynamic applications introduce friction and wear that aren't present to the same degree in static sealing. Speed, frequency of movement, lubrication and surface conditions may therefore become important considerations.

If movement is involved, explain how the components move and how frequently the equipment operates.

8. What Durometer Is Required?

Durometer describes the hardness of an elastomer.

A softer material may compress and conform differently than a harder compound. A harder material may offer advantages in certain pressure or wear conditions but may not behave the same way in every sealing configuration.

If your drawing specifies a durometer, include it in your request.

If it doesn't, information about the application can help determine what hardness range may be appropriate.

This is another reason simply asking for a “rubber O-ring” isn't enough. Two O-rings made from the same general elastomer family can still behave differently depending on the specific compound and hardness.

9. How Tight Are the Tolerances?

Not every application requires unusually tight tolerances, and specifying tolerances that are more restrictive than necessary can affect manufacturing options and cost.

On the other hand, applications with precise groove geometry or critical sealing requirements may demand tighter dimensional control.

If tolerances are important, communicate them clearly on the drawing or RFQ.

If you're unsure, discuss the assembly and sealing requirements with the manufacturer rather than automatically specifying the tightest tolerance possible.

10. How Many Custom O-Rings Do You Need?

Quantity matters when requesting a quote.

Are you looking for a handful of replacement O-rings for existing equipment? A prototype quantity for product development? Several hundred parts? Thousands or recurring production volumes?

Manufacturing methods and economics can change significantly with volume.

Providing realistic quantities allows your manufacturer to evaluate the project appropriately and may also help you compare pricing at different volume levels.

If you expect ongoing demand, include estimated annual usage along with the quantity required for the initial order.

Don't Know Every Answer? That's Okay.

One of the most important things to understand about ordering custom O-rings is that you don't necessarily need to arrive with a completely finished specification.

In many real-world situations, the conversation begins with something much less complete:

“We have this old O-ring that needs to be replaced.”

“This standard size keeps leaking.”

“We have a drawing but don't know which elastomer to specify.”

“This seal works until the equipment gets hot.”

Those details are useful.

A custom sealing manufacturer isn't just receiving dimensions. Understanding the application can help identify questions that need to be answered before manufacturing begins.

A Better Custom O-Ring RFQ Starts With the Application

The more relevant information you can provide upfront, the easier it is to evaluate your custom O-ring requirements.

Before requesting a quote, gather as much of the following information as you reasonably can:

• Inside diameter and cross-sectional diameter

• Drawing, specification, part number or physical sample

• Preferred material, if known

• Durometer requirements, if specified

• Minimum and maximum operating temperatures

• Chemicals, fluids or other substances the O-ring will contact

• Operating pressure and potential pressure spikes

• Static or dynamic sealing conditions

• Dimensional tolerances

• Initial order quantity and anticipated annual volume

• Any industry, testing or documentation requirements

You may not have every answer. The goal is to give your manufacturer enough information to understand what the seal actually needs to accomplish.

Custom O-Rings From Midwest Gasket

Midwest Gasket works with customers requiring custom sealing solutions for a wide range of industrial applications. Whether you're sourcing a custom O-ring for a new design, replacing a difficult-to-find component or looking for a dependable production supplier, the process begins with understanding your application's requirements.

Providing dimensions, operating conditions, material requirements, quantities and available drawings or samples can help move the project from inquiry to quote more efficiently.

And when you're not sure exactly what to specify, start with what you do know.

Need custom O-rings for an upcoming project? Contact Midwest Gasket with your drawing, specifications, sample or application requirements to begin the quoting process.