How should you verify that a sampling pump flow rate is within specification?

• A. Use a flow meter after sampling only.
• B. Use a calibrated flow meter before and during sampling; record flow and ensure within range.
• C. Check the visual gauge only.
• D. Estimate flow based on pump power.

Answer: (B)

Verifying the pump’s flow rate with a calibrated meter before and during sampling ensures the collected sample volume is accurate. Using a calibrated flow meter in-line lets you set the desired rate before you start and then continuously or intermittently check that the rate stays within the specified range throughout the sampling period. This objective measurement is essential because the actual flow can drift due to backpressure from filters, changes in tubing, temperature, or pump wear.

Relying on a visual gauge is unreliable because gauges can be misread, may not be calibrated, and don’t provide a precise, recorded value. Estimating flow from pump power is also inaccurate since pump output varies with backpressure and environmental conditions, and it doesn’t reflect the true flow reaching the sampling media. Recording the flow readings provides documentation that the sample met the protocol and helps identify any adjustments needed during the run.