Rotary Screw

Two helical rotors (male/drive and female/idler) mesh in a precision-bored housing. Air enters at the inlet port, is sealed between rotor lobes and the housing, and compressed as the lobe volume shrinks toward the discharge port. Oil-flooded types use oil for sealing, cooling, and lubrication.

Single-stage oil-flooded is 85–95% efficient at full load. VSD units save 15–35% energy vs fixed-speed on variable demand. Efficiency falls sharply below 40% load — match receiver and controls to the load profile.

Best for continuous duty (>50%) and high CFM. Oil-flooded for general plant air; oil-free (two-stage dry or water-injected) for food, pharma, electronics. Size a VSD where demand varies 30–100%.

• Male & female rotors (airend)
• Oil separator (flooded)
• Oil cooler & aftercooler
• Minimum pressure valve
• Inlet (modulating) valve
• Thermostatic valve
• Controller (PLC)
• VSD (optional)

• High discharge temp → low oil, blocked cooler, fan failure, faulty thermostatic valve
• Oil carryover → failed separator element, overfilled sump, scavenge line blockage
• Won't load → inlet valve stuck, solenoid failure, low system demand
• Short cycling → undersized receiver, leak in control line

• Daily: check oil, separator differential, temps
• 2,000 hrs: change oil filter, air filter, oil
• 4,000–8,000 hrs: separator element, coolant analysis
• Annual: airend vibration check, valve inspection

• Never run a flooded screw below 40% load — short cycling kills bearings
• Separator differential >8 PSI means replace the element now
• Sample oil every 4,000 hrs — rising metals trend bearing wear