How to Choose the Right O-Rings for Your Spray Foam Gun
O-Ring School – Why All O-Rings Are Not the Same for your particular application. Choosing the Wrong O-Ring Can Damage Your Spray Foam Gun By SPF Depot Choosing the correct O-ring material, durometer, and chemical resistance can extend seal life in Fusion AP, PMC AP2, PX7, and other spray foam guns. We offer many types of O-rings at SPF Depot. There is no shortage of places to buy O-rings—but there is a shortage of places that truly understand them.
The most commonly advertised material in our industry is Viton® / FKM. What many people don’t realize is that “Viton” is not just one magic material. There are multiple recognized families of FKM compounds, including specialty grades such as Extreme, and there are hundreds of commercial formulations plus many proprietary blends. Add in multiple curing methods, different hardness ratings (durometers), fillers, and chemical exposures—and suddenly there is no such thing as one O-ring that is best for everything.
Why This Matters in Spray Foam Equipment Our industry exposes seals to all kinds of chemicals: Brake cleaner Carb cleaner Solvents Resin-side materials ISO-side materials Lubricants Heat High pressure That means material selection matters.
As an Example I’m mainly referring here to the Graco Fusion AP gun, though many concepts apply to GX7, GAP, and others. Most seals inside a foam gun are static seals. That means they simply sit in place and seal—there is little or no movement.
Examples of seals with actual movement are limited to: Trigger valve spool Front air cap Piston seals And even those are generally supposed to see only air and some moisture from the air system. The Most Critical O-Rings: Wetted Seals - the ones that actually contact chemicals.
These include: Side seal Side cartridge Check valve These seals see the harshest environment and deserve the best materials.
Cheap Seal Kits vs Real Materials We stock some individual O-rings that cost over $2.50 each. So when someone sells a full seal kit for $10 and claims: “It’s the same material the OEM uses.” …it usually isn’t.
We work with a forensic engineering firm that analyzes seal materials, chemical solvents for chemical compatibility. Using FTIR spectroscopy, we’ve tested competitor and OEM seals.
What we found: Some OEM O-rings are standard compounds Some are proprietary engineered blends Some are not available off-the-shelf Anyone claiming to have the exact same blend as Graco without proof is not being honest, not to mention violating Patent laws that Graco takes seriously.
What SPF Depot Offers We stock carefully selected compounds including:
Premium FKM A strong general-purpose high-performance fluorocarbon option.
Viton Extreme® A patented proprietary Chemours material engineered for harsher chemical environments. (Chemours is the former DuPont chemicals division that received brands such as Viton™, Teflon™, and Ti-Pure™.)
What We Do NOT Use We do not offer Buna-N rubber in these applications. Why? Because common greases and chemicals can swell Buna, reducing seal life and causing fitment issues.
Durometer Matters: 70 vs 90 We offer two hardness ratings: 70 Durometer - Industry standard and common for many applications.
As rubber gets hot, it gets softer—just like a garden hose feels softer in August than in December. Combine heat + pressure + softer seals = bypass and leakage risk. That’s where 90D seals shine.
We especially recommend 90D for: Side seals Side cartridges Check valves Of those, the side seal is often the most critical. Does Color Matter? Usually, very little. Brown Viton is common, but O-rings can also be: Black Green Yellow Orange Custom colors
We buy 20,000-piece lots at a time. We can specify colors if desired. We once acquired a German company and received many green rear-cap O-rings. Some customers now insist the green ones are “better.” I have no clue as to why.
That rear cap seal is a static thread seal that sees no fluid, no pressure cycling, and almost no abuse.
Color does not improve performance.
Replace O-Rings Before Failure If you remove an O-ring and it is: Hard Brittle Cracks during removal Breaks when stretched …it should have been replaced earlier. This often means chemical attack or solvent exposure.
Final Thought Not all O-rings are the same. Material, cure system, hardness, chemical exposure, pressure, and heat all matter. That’s why SPF Depot offers multiple options instead of pretending one cheap seal works for every customer.
SPF Depot sells O-rings based on real-world performance—not marketing myths.
