Desiccant dryer PM
Desiccant inspection, valve/muffler service, and purge tuning on a heatless twin-tower.
This guide is general field reference for trained, qualified service technicians. It is not a substitute for the original equipment manufacturer's service manual, applicable codes (NEC, OSHA, ASME, local), or the judgment of a licensed professional. Procedures, torque values, pressures, refrigerants, and safety requirements vary by make, model, jurisdiction, and revision. Always verify against current OEM documentation and follow your employer's safety program. Working on compressed-air, electrical, pressure-vessel, and refrigerant systems can cause serious injury or death. By using this guide you accept all risk; AirCompDX and its authors disclaim all warranties and are not liable for any damage, injury, loss, or code violation arising from its use.
Tower switching valves cycle on a 5–10 minute timer; depressurize and lock controller out before opening any tower.
- Calibrated dewpoint meter (-40°F or better)
- Inline flow meter
- Socket set
- Desiccant fill (activated alumina or 13X molecular sieve)
- Purge muffler
- Switching valve seats
- 1LOTO and depress
Lock the controller out, isolate inlet and outlet, vent both towers to 0 psi.
- 2Inspect desiccant
Pull the top port plug, sample the top inch of bed. Powdered, fused, or oil-soaked = full refill. Oil contamination upstream means a missing or failed coalescing prefilter.
- 3Service mufflers
Mufflers plug with desiccant dust and choke the purge — replace at every major PM. A plugged muffler raises tower regen pressure and ruins dewpoint.
- 4Check switching valves
Listen for crisp tower switching. Hissing through the purge between switches = leaking switching valve seat.
- 5Verify purge rate
Heatless dryers use 15–20% of rated flow as purge. Verify with inline flow meter; trim per OEM if purge is off.
- 6Confirm dewpoint
After 4 hours of cycling, log PDP at outlet — target ≤ -40°F PDP for instrument air, ≤ -100°F for breathing air with a CO catalyst downstream.
