Flow Switch Troubleshooting Guide

Possible Causes

• Vibration from nearby pumps or compressors
• Electrical noise on signal wiring
• Setpoint set too close to normal operating flow
• Paddle or vane resonating at pipe vibration frequency

Corrective Actions

• Install vibration-isolating mounting bracket
• Use shielded cable; verify proper grounding
• Increase setpoint margin — 20% above minimum acceptable flow
• Switch to a different paddle size or style

Possible Causes

• Setpoint drifted above actual flow
• Paddle or vane fouled with scale or debris
• Magnetic reed switch failed open
• Wiring fault — open circuit

Corrective Actions

• Verify setpoint with calibrated flow meter
• Clean or replace paddle/vane
• Test switch continuity with multimeter; replace if failed
• Inspect wiring for breaks, corrosion, or loose terminals

Possible Causes

• Spring fatigue over time
• Temperature cycling affecting spring rate
• Fluid density change (temperature or concentration)
• Partial fouling of paddle reducing effective area

Corrective Actions

• Replace spring; consider upgrade to adjustable setpoint model
• Verify fluid temperature at switch location
• Recalculate setpoint for actual fluid density
• Clean paddle; inspect for erosion or corrosion

Possible Causes

• Wetted materials incompatible with process fluid
• Galvanic corrosion between dissimilar metals
• Stress corrosion cracking in stainless steel with chlorides
• Erosion from high-velocity or abrasive fluid

Corrective Actions

• Upgrade to compatible wetted materials (PVDF, Hastelloy, titanium)
• Use all-same-material wetted components
• Switch to duplex stainless or Hastelloy for chloride service
• Reduce velocity or switch to non-intrusive flow detection

Possible Causes

• Incorrect wiring (NO vs. NC confusion)
• Voltage or current exceeds switch rating
• Ground loop causing erratic behavior
• Moisture ingress into terminal housing

Corrective Actions

• Verify wiring against switch datasheet — confirm NO/NC configuration
• Check switch electrical ratings vs. load
• Isolate signal ground; use isolated relay
• Inspect and reseal conduit entry; replace gaskets