Why Gas Volume in a Syringe Is Less Than Calculated

Why Gas Volume in a Syringe Is Less Than Calculated

— A Closer Look at Syringe Air Retention, Loss, and Compression Factors

In prefilled syringe manufacturing and injectable device testing, it's not uncommon to observe that the actual gas volume inside a syringe is less than theoretically calculated.

This seemingly small deviation can have major implications for product quality, regulatory compliance, and delivery accuracy — especially in biotech, vaccine, or aesthetic applications.

At Sunrise Medical, we frequently support clients in understanding and mitigating this phenomenon during both design validation and commercial production.

Common Reasons for Gas Volume Discrepancy

1. Micro Leakage at the Plunger or Tip

• Imperfect Luer tip sealing or plunger head compression may allow slow gas escape, especially during shipping, autoclaving, or vacuum testing.

• This is more common in low-viscosity drugs or incompletely annealed glass barrels.

2. Compression of Air Due to Atmospheric Pressure or Temperature

• Boyle’s Law in practice: gas volume can decrease under external pressure (e.g., terminal sterilization, altitude changes).

• In many cases, what appears as "volume loss" is actually gas compression, not leakage.

3. Syringe Internal Volume Tolerance

• Even a ±0.05 mL deviation in barrel ID or cone shape can lead to perceived loss.

• Tolerances stack from tip to flange — requiring strict control per ISO 11040.

4. Incomplete Filling or Unintended Air Evacuation

• In high-speed filling lines, micro-bubble displacement during silicone-coated plunger insertion may unintentionally push air out.

• Some drugs (e.g. biologics) may trap microbubbles less efficiently than saline.

How Sunrise Medical Controls These Variables

As a manufacturer of custom prefilled syringe barrels, we implement:

• Plunger seal leak testing with pressure decay analysis

• Dimensional control of syringe cones and barrels within ±0.03 mm

• Birefringence-based annealing inspection to ensure uniform cooling

• Siliconization optimization (spray vs crosslinked) to prevent internal gas escape

• Volume verification protocols per ISO 7886-1 & 11040

 Key Takeaway

A mismatch in syringe gas volume is rarely a single fault — it's a multi-factor result of physics, materials, and process design.

At Sunrise Medical, we work with clients from design concept to finished device to ensure every microliter is accounted for — with proven tools for volume accuracy, gas integrity, and sealing performance.

If you're experiencing gas volume issues in your syringe project, contact our technical team for a collaborative assessment or OEM optimization support.