Decision Tree: Low / No Flow
Symptom: low flow alarm, no sample flow, slow response, unstable reading.
Safety: Follow permit rules before opening sample lines. Depressurize safely.
Isolation steps
1) Confirm sample source pressure is available. Check upstream isolation valves are open.
2) Check filter condition: if DP high or bowl dirty, replace/clean filter and re-test flow.
3) Check regulator and needle valve settings: ensure not fully closed and not hunting.
4) If pump fitted:
- Check pump power and status
- Check pump diaphragm/vanes (weak pump = low flow)
- Check pump inlet blockage / moisture trap full
5) Check for line blockage / condensation:
- Frozen/condensed lines restrict flow
- Heat tracing failure causes condensation
- Drain moisture traps and inspect tubing
6) After restoring flow:
- Allow reading to stabilize
- Verify with calibration gas
- Confirm alarms clear and trend stable