There’s a good chance you’re sitting near one right now. Your car, the coffee machine down the hall; they’re all probably held together, in some small but crucial way, by an O-ring. These little rubber rings do an unglamorous job. They sit in a groove and prevent leaks. Nobody notices them until they fail.
But not every O-ring does the same job. A seal handling compressed air faces very different conditions to one containing hot hydraulic oil under high pressure.
Here we break it down by application. Once you know what the seal is exposed to, choosing the right material becomes much easier.
Hydraulics: Where the Pressure Never Lets Up
Hydraulic systems are relentless. You’ve got oil under serious pressure, moving parts sliding past static ones, and heat building up from all that mechanical work. An O-ring in a hydraulic cylinder is holding back fluid, all while a piston rod slides past it thousands of times a day.
This is dynamic sealing at its toughest. The ring needs to resist extrusion (being squeezed out through the tiny gap in the groove under pressure), withstand petroleum-based oils, and withstand the heat that hydraulic systems generate as a matter of course.
What To Use For Hydraulics
Nitrile O-rings are the best type of seal for this work. They’re built for the combination of oil, moderate heat, and pressure, which is why you’ll find them in excavators, presses, and just about anything else that runs on hydraulic power.
Once operating temperatures start pushing past roughly 120°C, or the fluid becomes more chemically aggressive, Viton FKM O-rings are often the better option. FKM offers stronger heat and chemical resistance for more demanding hydraulic applications.
Pneumatics: Different Challenges at Lower Pressure
Swap hydraulic oil for compressed air, and you’d think the job gets easier. In some ways, it does. Pneumatic systems generally operate at lower pressures than hydraulic systems, and air is much gentler on rubber than oil-based fluids.
But pneumatics bring their own challenges.
Compressed air lines can run dry, reducing natural lubrication for the seal. Cycling can be rapid and constant. And depending on where the equipment is used, you might be dealing with ozone exposure or large temperature swings that a purely oil-resistant compound wouldn’t cope with.
What To Use For Pneumatics
Silicone O-rings often show up in pneumatic applications that need to handle temperature swings or where food-grade or medical-grade compliance matters. This includes packaging lines, lab equipment, or cleanroom machinery. For general workshop air tools and standard pneumatic cylinders, nitrile performs very well too.
Pumps: Sealing Across Changing Conditions
If hydraulics are relentless, pumps are relentless and unpredictable. Pump seals have to handle movement, vibration and a much wider range of media, from clean water to caustic chemicals and abrasive slurry.
Centrifugal, gear, and diaphragm pumps all rely on sealing rings to keep the media where it belongs and prevent it from entering bearings, motors, or the surrounding environment.
What To Use For Pumps
For pumps moving standard oils and fuels, Nitrile or Viton usually covers them. But once you’re pumping hot acids, sour gas, or high-pH chemicals, it’s worth considering FEPM (Aflas) O-rings, which handle steam and sour service noticeably better than standard fluoroelastomers.
And for pumps handling the most aggressive chemicals in a plant, especially where seal failure could create a serious safety risk, FFKM is often the best choice.
Process Equipment: The Chemical Curveball
Process equipment brings a different set of sealing challenges. We’re talking reactors, valves, and pipework in chemical plants, pharmaceutical facilities, and semiconductor fabs; environments where the media can actively break the seal down chemically.
General-purpose O-rings simply won’t cut it.
A seal in a semiconductor vacuum line needs low outgassing to help protect a clean process. In pharmaceutical equipment, seals need to withstand repeated sterilisation and chemical cleaning. In a chemical reactor, the same component is exposed to strong bases over the course of operation.
What To Use For Process Equipment
For this tier of application, it’s worth talking to an FFKM O-rings supplier directly. FFKM resists an enormous range of chemicals and holds up at temperatures that would destroy a standard rubber seal, which is why it costs more and why it’s worth it when the application calls for it.
Getting the Size Right Matters Just as Much
You can pick the perfect material for your application and still end up with a leak because the size was slightly off. O-ring sizing comes down to two measurements: inside diameter and cross-section, and getting either one wrong means a seal that’s either too loose to do its job or so tight it extrudes and fails early.
If you’re not sure where to start, it’s worth talking to experts on how to measure O-ring sizes properly before you order anything.
And if you’re working with older equipment where the original specification is long gone, finding replacement O-rings can take a bit of detective work. Having the correct groove measurements on hand makes the process much easier.
The Right Seal for the Job
Matching the material and size to the job is the difference between a seal that lasts for years and one you’re replacing every few months.
If you’re not sure which material or size suits your equipment, browse our range of O-rings for sale or get in touch with our team directly.
Industrial Experts is an industrial seals and gaskets supplier based in Melbourne. We can talk through your application and point you toward the right compound the first time, leaving you with more savings and less hassle down the road.
