Air Bubbles in the Sample Cell or U-Tube

Air Bubbles in the Sample Cell or U-Tube

Air bubbles in the sample path can cause unstable readings, failed verification, slow measurements, or poor repeatability. In many cases, the issue is caused by worn tubing, loose fittings, contamination, improper sample loading, or a damaged sample cell/U-tube.

Common Symptoms

• Visible bubbles in the sample cell, U-tube, or tubing
• Unstable or inconsistent results
• Failed zero or air/water verification
• Slow measurements or timeouts
• A bubble that appears to stay in the same spot

Common Causes

• Worn peri pump tubing
• Loose fittings, nozzles, or connections
• Dirty or contaminated sample cell/U-tube
• Improper sample loading
• Incorrect hose or cap orientation
• Damaged sample cell or U-tube
• Refractometer prism cap not correctly orientated (Automation/AlcoTest)

What to Do

1. Check tubing and fittings
Inspect the sample path for loose, worn, or damaged tubing, fittings, and nozzles. Replace worn peri pump tubing if needed.

2. Clean the sample cell or U-tube
Thoroughly clean and flush the sample path using the appropriate cleaning procedure for your instrument and application. Rinse well and fully dry before retesting.

3. Review sample loading
Use a fresh syringe when possible and load the sample slowly to avoid introducing air.

4. Refractometer Cap Orientation (Automation/AlcoTest)

The refactometer orientation of the flow through cap must havbe the inlet flow on the bottom port and the outlet flow from the top port.

4. Run verification
After cleaning and inspection, perform the applicable zero or air/water verification.

• If verification passes, resume testing
• If the issue remains, contact support

When to Contact Support

• Bubbles remain after cleaning and verification
• The bubble appears fixed in one location
• The instrument will not complete verification or adjustment
• The pump is not pulling sample properly
• You suspect a damaged U-tube, sample cell, or fitting

Troubleshooting Flowchart

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How can we further assist you?

Give us a call, we are happy to help! (973) 584-1558 Monday - Friday 8:30AM - 5PM EST or open a service ticket. Request a quote for a field service visit or replacement part.