Rotary screw airend major PM

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Rotary screw airend major PM

Coupling, shaft seal, inlet valve service, and bearing inspection on a lubricated rotary screw airend.

Category
Rotary Screw
Time
6–8 hr
Level
Advanced
Disclaimer — read before starting

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.

Vent sump pressure through the bleed valve and verify 0 psi at the gauge before opening any fluid line. Sump fluid is hot under load — let cool 30 minutes minimum.

Tools
  • Coupling alignment dial set or laser
  • Bearing puller / induction heater
  • Oil-analysis sample bottle (kept for trend)
  • Inlet valve rebuild kit per OEM
  • Torque wrench up to 150 ft-lb
Parts
  • Coupling element (rubber spider or steel grid)
  • Inlet/blowdown valve rebuild kit
  • Shaft seal (if leaking)
  • Sump fluid charge (OEM-spec coolant)
  • Air/oil separator element
  • Coalescing oil filter
  • Inlet air filter
Procedure
  1. 1
    Pre-shutdown sample

    Pull a hot oil sample for analysis before shutdown — wear-metal trend tells you whether to expect bearing work this PM cycle.

  2. 2
    LOTO and vent

    E-stop, open disconnect, LOTO. Open the manual blowdown until the sump gauge reads 0 and you hear no whoosh from the separator vent.

  3. 3
    Drain fluid and filter changes

    Drain sump warm (~100°F) for full evacuation. Replace oil filter, separator element (torque to OEM spec — over-torque crushes the seal), and inlet filter.

  4. 4
    Inlet/blowdown valve service

    Pull the inlet valve, replace diaphragm or piston seals per OEM kit. Check the blowdown solenoid filter and the orifice — blocked orifice = sump won't depressurize on stop.

  5. 5
    Coupling inspection

    Pull the coupling guard. Inspect the spider (rubber): any cracking, missing legs, or set means replace. For grid couplings, inspect the grid for fatigue and the housing for wear.

  6. 6
    Bearing condition check

    With the airend stopped, rotate by hand at the male shaft (some units have a turning lug). Listen and feel for roughness. Vibration baseline: take ISO 10816 readings before and after — rising trend = bearing work next PM.

  7. 7
    Shaft seal inspection

    Any visible fluid streaks below the airend shaft seal = replace. A weeping seal on a flooded screw means contaminated coupling and risk of rust on the motor shaft.

  8. 8
    Refill and bump

    Refill sump to top of sight glass with OEM-spec coolant — do not mix brands or chemistries. Bar over by hand if accessible.

  9. 9
    Realign coupling

    Set dial or laser alignment to OEM spec (commonly ≤0.002" parallel, ≤0.0005"/in angular). Recheck after 24 h of operation — soft-foot and thermal growth often show up overnight.

  10. 10
    Commissioning run

    Start, run unloaded 10 min, then loaded. Verify sump pressure builds to setpoint, discharge temp stabilizes (typ. 180–200°F), and amp draw is within nameplate.

  11. 11
    Post-PM sample and log

    Pull a fresh oil sample 50 hours after PM as a new baseline. File alignment readings, vibration baseline, and amp draw in the unit PM record.

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