Few things are more frustrating than fitting a new O-ring… only for the leak to still be there afterwards.

In many cases, the issue isn’t the fitting itself — it’s the seal selection, installation, or operating conditions.

Here are some of the most common reasons O-rings fail or leak, and how to avoid them.

---

1. The O-Ring Is the Wrong Size

One of the most common causes of leaks is simply using the wrong size O-ring.

Even a small difference in:

• inner diameter (ID)
• cross section (CS)
• groove fit

can prevent the seal from compressing correctly.

An undersized O-ring may stretch too much, while an oversized seal may twist or pinch during installation.

Tip:

Always measure:

• ID (inner diameter)
• OD (outer diameter)
• CS (cross section)

before replacing an O-ring.

---

2. The Wrong Material Was Used

Not all O-rings are designed for the same fluids or temperatures.

Using the wrong material can lead to:

• swelling
• cracking
• hardening
• rapid seal failure

Common examples:

A leaking O-ring is often the first sign of material incompatibility.

---

3. The O-Ring Has Been Damaged During Installation

O-rings can easily become damaged during fitting.

Common installation damage includes:

• cuts
• pinching
• twisting
• abrasion against sharp edges

Even small marks can create a leak path under pressure.

Tip:

Light lubrication and careful installation help prevent damage.

---

4. The Seal Groove Is Dirty or Damaged

A perfect O-ring won’t seal properly if the groove or sealing surface is damaged.

Check for:

• dirt or debris
• scratches
• corrosion
• old seal material

Any imperfection can prevent the O-ring from sealing evenly.

---

5. The O-Ring Is Too Soft for the Pressure

In higher-pressure systems, softer O-rings can deform or extrude into clearances.

This is where harder compounds such as NBR 90 are often preferred.

Typical signs include:

• flattened edges
• extrusion marks
• recurring leaks under pressure

For hydraulic or compressed air systems, hardness matters.

---

6. Temperature Is Causing Seal Failure

Excessive heat can harden or degrade standard nitrile O-rings over time.

If the application runs hot — such as:

• engines
• gearboxes
• turbo systems

— a higher temperature material like FKM (Viton®) may be required.

Likewise, extremely cold environments can reduce flexibility and sealing performance.

---

7. The O-Ring Has Simply Worn Out

O-rings are wear items.

Over time they naturally:

• compress permanently
• lose elasticity
• harden
• crack

This is especially common in:

• older machinery
• automotive systems
• hydraulic equipment

Replacing ageing seals before failure helps prevent leaks and downtime.

---

How to Prevent O-Ring Leaks

A few simple checks make a huge difference:

✔ Use the correct size
✔ Choose the right material
✔ Inspect grooves and mating surfaces
✔ Avoid damaging the seal during installation
✔ Match hardness to pressure requirements

Good sealing starts with proper selection.

---

Need Help Choosing the Right O-Ring?

At Seal With Selo, we stock:

• NBR O-rings
• FKM (Viton®) O-rings
• Silicone O-rings
• EPDM O-rings
• NBR 90 high-pressure O-rings

Available in:

• metric sizes
• BS (imperial) sizes
• individual quantities
• UK stock with same-day dispatch before cut-off

---

In Summary

Most O-ring leaks come down to:

• incorrect sizing
• incorrect material choice
• installation damage
• pressure or temperature mismatch

Understanding the cause of the leak is the first step to solving it properly.