Screw Compressor Maintenance

Preventive maintenance is essential to maximize compressor lifespan, efficiency, and reliability.

Maintenance Philosophy

         Cost
           │
           │    ╱ Failure cost
           │   ╱  (no maintenance)
           │  ╱
           │ ╱         ╱ Over-maintenance cost
           │╱         ╱
           │╲       ╱
           │ ╲     ╱
           │  ╲   ╱
           │   ╲ ╱  ← Optimal point
           │    ●
           └──────────────────────→ Maintenance
              Little          Much

Goal: Find the balance between maintenance cost and failure cost.

Maintenance Intervals

Lubricated Compressors

Component	Interval	Action
Inlet filter	2,000-4,000 h	Change
Oil	4,000-8,000 h	Change
Oil filter	4,000-8,000 h	Change
Oil separator	4,000-8,000 h	Change
Belts	4,000-8,000 h	Inspection
Inlet valve	8,000-16,000 h	Service/kit
Minimum pressure valve	8,000-16,000 h	Service/kit
Thermal valve	16,000-24,000 h	Service
Bearings	40,000-60,000 h	Replacement
Airend overhaul	40,000-80,000 h	Rebuild

Oil-Free Compressors

Component	Interval	Action
Inlet filter	2,000-4,000 h	Change
Gearbox oil	8,000-16,000 h	Change
Oil filter (gearbox)	8,000-16,000 h	Change
Shaft seals	16,000-24,000 h	Inspection
Timing gears	24,000-40,000 h	Inspection
Bearings	24,000-40,000 h	Replacement
Rotor coatings	24,000-40,000 h	Inspection
Airend overhaul	25,000-50,000 h	Rebuild

Daily/Weekly Maintenance

Daily Checklist

Item	What to check	Action if abnormal
Oil level	In range (sight glass)	Add oil
Discharge temperature	<212°F (100°C)	Investigate cause
Operating pressure	In range	Check demand
Abnormal noises	No knocking	Stop and investigate
Vibrations	Normal	Investigate cause
Visible leaks	No leaks	Repair
Condensate drained	No accumulation	Drain/check trap

Weekly Checklist

Item	What to check
Inlet filter pressure drop	<0.7 psi (50 mbar)
Separator pressure drop	<7 psi (0.5 bar)
Oil temperature	120-160°F (50-70°C) at injection
Operating hours	Record
Load/unload cycles	Record
Electrical consumption	Compare to history

Component Maintenance

Inlet Filter

Signs change is needed:

• Pressure drop >0.7 psi (50 mbar)
• Dark/saturated color
• Visible damage

Procedure:

1. Shut down compressor
2. Release residual pressure
3. Remove old filter
4. Clean housing
5. Install new filter
6. Verify proper seal

Don't Clean Filters

Inlet filters should NOT be cleaned and reused. The filter media is damaged and loses efficiency.

Compressor Oil

Oil analysis recommended every 2,000 hours:

Parameter	Limit	Indicates
Viscosity	±15% of new	Thermal degradation
TAN (acidity)	<2.0 mg KOH/g	Oxidation
Water	<500 ppm	Condensation/leaks
Particles	ISO 18/16/13	Wear/contamination
Wear metals	Per baseline	Component wear

Oil change:

1. Run until normal temperature
2. Shut down and drain while hot
3. Change oil filter
4. Refill with new oil
5. Run and check level

Separator Element

Signs change is needed:

• Pressure drop >12 psi (0.8 bar)
• Excessive oil carryover
• Oil in compressed air

Procedure:

1. Fully depressurize
2. Remove tank cover
3. Extract old element
4. Clean tank interior
5. Check scavenge tube
6. Install new element with gasket
7. Torque correctly

Drive Belts

Inspection:

• Correct tension (specified deflection)
• No cracks or wear
• Pulley alignment

Change:

• Always change complete set
• Check pulley condition
• Adjust tension per specification

Airend Overhaul

When to Overhaul?

Indicator	Typical value
Operating hours	40,000-80,000 h
Degraded efficiency	>10% consumption increase
Increased noise	Notable change
Increased vibration	Out of specification
Elevated temperature	>10°F (5°C) above normal
Oil analysis	High wear metals

What's Included

Component	Action
Rotors	Inspection, polish or replace
Bearings	Complete replacement
Seals	Complete replacement
Housing	Inspection, refinish if needed
Gears	Inspection, replace if needed

Overhaul Options

Option	Cost	Time
On-site overhaul	$$	3-5 days
Airend exchange	$$$	1 day
New airend	$$$$	1 day
Remanufactured airend	$$	1 day

Troubleshooting

High Discharge Temperature

Cause	Solution
Clogged inlet filter	Change filter
Low oil level	Add oil
Dirty cooler	Clean cooler
Defective thermal valve	Replace valve
High ambient temperature	Improve ventilation
Degraded oil	Change oil

High Oil Consumption

Cause	Solution
Saturated separator	Change separator
Clogged return line	Clean/unclog
Oil level too high	Drain excess
Wrong oil	Change to correct oil
Worn airend seals	Overhaul

Low Air Production

Cause	Solution
Clogged inlet filter	Change filter
Defective inlet valve	Repair/replace
Airend internal leaks	Overhaul
System leaks	Detect and repair
High separator ΔP	Change separator

Abnormal Noises

Noise	Possible cause	Action
Metallic knocking	Damaged bearings	Stop immediately
Squealing	Loose/worn belts	Adjust/change
Hissing	Air leaks	Locate and repair
Humming	Electric motor	Check motor bearings

Maintenance Records

Data to Record

Data	Frequency
Operating hours	Daily
Discharge temperature	Daily
Operating pressure	Daily
Electrical consumption	Weekly
Consumable changes	Each event
Oil analysis	Each sampling
Failures and repairs	Each event

Record Benefits

1. Failure prediction - Abnormal trends
2. Interval optimization - Adjust to real conditions
3. Warranties - Maintenance documentation
4. Budgeting - Cost planning
5. Efficiency - Identify degradation

Maintenance Cost

Typical Budget

$$\text{Annual cost} \approx 3-5\% \times \text{Compressor value}$$

Typical breakdown:

Component	% of annual cost
Filters (inlet, oil)	15-20%
Oil	20-25%
Separator	15-20%
Labor	25-30%
Other (belts, valves)	10-15%

Cost of NOT Maintaining

Failure	Approximate cost
Premature overhaul	$10,000-50,000
Bearing failure	$5,000-20,000
System contamination	$5,000-30,000
Production downtime	Variable (very high)