Overview
High‑pressure PEEK fittings are widely used in HPLC because of their chemical compatibility and convenience, but their actual pressure capability depends on both the receiving port (female part) and the tubing material being tightened into the fitting.
Since these variables vary by system, no single maximum pressure value applies universally.
Pressure Characteristics of High‑Pressure PEEK Fittings
General Pressure Behavior
- High‑pressure PEEK fittings with a 10‑32 threaded connection typically hold PEEK tubing at pressures higher than the tubing’s own burst pressure, making the tubing the limiting factor rather than the fitting.
- System safety depends on not exceeding the manufacturer’s recommended pressure rating for the instrument.
Material Influence
- PEEK tubing provides strong and consistent sealing capability with PEEK fittings.
- Stainless‑steel tubing in a PEEK nut behaves differently due to its harder surface.
PEEK Nut on Stainless‑Steel Tubing
Performance Considerations
- Stainless‑steel tubing may slip out of the connection when used with a PEEK nut, depending on tightening force, surface finish, and alignment.
- Typical slip or burst pressures for this combination fall around 5000–6000 psi, making it less secure than when using PEEK tubing.
When This Combination Is Used
- Limited to scenarios where chemical compatibility and convenience outweigh maximum pressure requirements.
- Not recommended for the highest‑pressure areas of an HPLC system.
Double‑Ferrule High‑Pressure Connections
Why Double‑Ferrule Designs Improve Performance
- A double‑cone ferrule grips tubing at two contact points instead of one.
- This increases stability and reduces the risk of tube slippage under high mechanical load.
Pressure Advantages
- A properly designed double‑ferrule connection increases pressure stability by approximately 25% over standard single‑ferrule or one‑piece fittings.
Recommended Uses
- Ideal for HPLC zones operating near instrument maximum pressure ratings.
- Especially valuable when maximizing grip on stainless‑steel tubing.
Safety Considerations
Operational Guidelines
- Avoid exceeding the pressure limits of your HPLC system, even if fittings and tubing can technically hold higher pressures.
- Always verify material compatibility, especially when mixing tubing types.
Best‑Practice Recommendations
- Use PEEK fittings with PEEK tubing for highest consistency.
- Use double‑ferrule systems when additional grip or stability is needed.
- Inspect tubing ends and fittings regularly for wear or deformation.
