Flow and Pressure Control Part 3. Measuring flow rates
Where to measure flows
78
Procedure: Measuring gas flows with a bubble meter
Tools:
• Bubble meter graduated at 1, 10, and 100 mL. Bulb half-filled with soapy
water.
• Adapter for detector or vent
• GC internal stopwatch
WARNING Do not measure hydrogen together with air or oxygen. This can create explosive
mixtures that may be ignited by the automatic ignitor.
To avoid this hazard:
Turn the automatic ignitor off before you begin.
Always measure gases separately.
1. Attach the inlet line of the bubble meter to the fitting where you will measure
flow. Use the appropriate adapter, if needed.
2. Hold the bubble flow meter vertically—squeeze and release the bulb to
create a meniscus in the bubble meter. Do this several times to wet the sides
before taking measurements.
3. Press [Time] to see the stopwatch screen. Squeeze the bulb.
4. Press [Enter] to start the stopwatch when the meniscus passes the START
(lowest) line in the bubble flow meter.
5. Press [Enter] again to stop the stopwatch when the meniscus passes the
1 mL, 10 mL, or 100 mL line.
6. Calculate the flow rate in mL/min from the 1/t value:
• If you used the 1 mL line, the flow rate in mL/min = 1/t.
• If you used the 10 mL line, the flow rate in mL/min = 10 × 1/t.
• If you used the 100 mL line, the flow rate in mL/min = 100 × 1/t.
7. Press [Clear] to reset the stopwatch. Repeat the measurement at least once
to verify the flow.
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