Choosing the Right De-airing Device for Your Triaxial Test System

Ensuring proper de-airing is essential in triaxial testing, as residual gas in the system can significantly reduce test accuracy and reliability.

To select the right de-airing device, lab engineers must consider vacuum level requirements, de-airing efficiency, sample throughput, and integration compatibility. This guide compares popular de-airing methods and provides technical insights to help you make the right choice.

Required Vacuum Level & Target Dissolved Gas

In triaxial tests, especially those following ASTM D4767¹ or BS 1377, proper saturation is vital. De-airing helps remove dissolved and entrapped air² from the pore pressure system and water supply.

• Target vacuum: Most systems aim for -70 to -85 kPa (gauge) to remove dissolved gases below saturation limits.
• Water degassing goal: Below 3 mg/L of dissolved oxygen is often targeted for sensitive soil specimens like clays.
• Importance: Inadequate de-airing leads to B-values under 0.95, affecting test validity.

Device Types Compared: Chamber, Inline Membrane, Recirculating Tank

Here’s how common de-airing device types compare:

Tip: Inline membrane systems save space and reduce contamination risks, but chamber units are more affordable and robust for general lab use.

Sizing for Throughput: Volume, Flow, and Heat

Choosing the right size depends on how much de-aired water your test requires per day.

• Daily water volume⁵: Estimate number of specimens × 500–1000 mL.
• Flow rate: Inline systems must match downstream flow needs (e.g., 100–300 mL/min).
• Heat considerations: Degassing systems running continuously can heat water. If sensitive, use cooling jackets⁶ or intermittent vacuuming.

Integration & Maintenance: Filters, Lines, and Standards

A de-airing device must seamlessly integrate with your existing setup:

• Tubing & connectors: Use non-permeable tubing (e.g., PTFE) to reduce reabsorption.
• Inline filters: Place 0.45μm filters downstream to prevent particulate contamination.
• Drain valves: Make sure excess air or foam can be released.
• Maintenance: Clean tanks weekly and replace membranes every 3–6 months depending on use.

Compliance Note: For labs under ISO/IEC 17025 or working on public infrastructure projects, documentation of water saturation level and maintenance logs is often required.

✅ Conclusion

Choosing the right de-airing device requires balancing vacuum performance, sample volume, and operational efficiency. Whether you opt for a vacuum chamber, inline membrane, or recirculating system, ensure that it matches your lab’s daily workload, integrates well with your triaxial setup, and supports easy maintenance.

A well-chosen de-airing system boosts B-value reliability, extends equipment lifespan, and ensures compliance with global testing standards.