In hydraulic systems, a tiny leak can turn into a costly failure. And when it comes to flat face fittings, a standard o ring just won’t cut it.
That’s why a flat face o ring kit is a must-have for any maintenance team working with high-pressure quick couplers, especially in mobile machinery and construction equipment.
Let’s explore when to use flat o rings, why they matter, and how to choose the right kit.
What is a flat face o ring?
A flat face o ring is a sealing ring with a square or flat cross-section designed specifically for hydraulic quick-connect couplings.
They’re commonly used in:
- ISO 16028 flat face couplings
- Caterpillar-style face seal fittings
- Mobile hydraulic equipment (e.g., excavators, loaders)
The flat profile allows full metal-to-metal contact while still maintaining a fluid-tight seal under extreme pressure.
Why use a flat face o ring instead of a standard one?
Flat face o rings eliminate the risk of extrusion and deformation that can occur with standard round-section o rings in couplings.
Compared to round o rings, flat seals:
- Stay seated in shallow grooves
- Provide uniform compression on flat mating surfaces
- Resist rolling and twisting during connection
This leads to fewer failures and longer service life in harsh working environments.
See more in our Hydraulic O Ring Kit Breakdown
What sizes are included in a flat face o ring kit?
Our flat face kits cover the most-used hydraulic coupling sizes.
| O Ring Size | Inner Diameter (ID) | Cross Section | Compatible Standard |
|---|---|---|---|
| #8 | ~13.64 mm | ~2.34 mm | ISO 16028 / SAE J1453 |
| #10 | ~17.17 mm | ~2.34 mm | Caterpillar, Komatsu |
| #12–20 | 20–34 mm | ~2.62–3.53 mm | High-flow flat couplers |
Each O Ring Kit includes 30 sizes, and flat face options can be added or customized.
Are flat face o rings reusable?
In theory—yes. In practice—don’t.
Hydraulic seals degrade with use. Reusing old o rings can lead to:
- Surface cracking
- Loss of elasticity
- Leaks under dynamic pressure
It’s safer to replace every time you disconnect, especially in heavy-use applications like construction, agriculture, or mining.
Which material is best for flat face hydraulic seals?
We recommend Viton for high heat and synthetic fluid resistance, and NBR for general hydraulic oil applications.
| Material | Temp Range | Oil Resistance | Pressure Rating | Notes |
|---|---|---|---|---|
| NBR | -40°C to 120°C | Good | Moderate-High | Cost-effective |
| Viton | -20°C to 200°C | Excellent | High | Great for CAT & ISO 16028 systems |
| PTFE | -200°C to 260°C | Excellent | High (Static) | Best for aggressive fluids |
Want to see more material comparisons?
Check our Viton/PTFE O Ring Guide
How does this relate to metric vs inch o ring kits?
Flat face fittings often use custom or metric dimensions. If your team uses both ISO and SAE equipment, get a kit that supports both standards.
Read: Metric vs Inch – Which Kit Fits Your Equipment?
Final Thoughts on Flat Face O Ring Kits
Flat face o rings aren’t optional—they’re essential. Whether you’re maintaining heavy-duty hydraulics or assembling OEM kits for resale, having the right flat seal on hand makes all the difference.
Get a Custom Flat Face O Ring Kit
Need a flat face o ring kit for Caterpillar, ISO 16028, or Komatsu-type couplings?
📩 Email: [email protected]
📱 WhatsApp: +86 17622979498
We support OEM branding, custom labeling, and low MOQ for hydraulic distributors.
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