The screw compressor's main cylinder houses a pair of parallel, intermeshing male and female rotors with helical grooves. There is minimal clearance between the rotors and between the rotors and the housing, theoretically eliminating metal-to-metal contact during operation. Structurally, screw compressors are more stable and quieter than traditional piston compressors.  

However, many users encounter abnormal noises during operation, such as metallic collisions, rhythmic knocking, or friction-induced screeching. These noises vary in sound and location depending on the underlying cause. This article briefly analyzes different noise sources and provides corresponding solutions for reference.  

1. Cause: Loose Belt (Belt-Driven Type)

Symptoms of Belt Slippage:  

(1) Burnt belt odor near the equipment, with belt debris on the ground.  

(2) Abnormal friction noise between the belt and pulley.  

(3) Fluctuating current due to uneven load distribution.  

Solution：

Adjust belt tension using the tensioning bolt (deflection < 5mm), avoiding over-tightening.  

 If slippage persists after adjustment, replace the belt.  

Note: Always replace all belts simultaneously to maintain uniform tension. Prevent oil from contacting belts or pulleys to avoid slippage.  

2. Cause: Oil Starvation in Screw Compressor

Oil starvation leads to direct metal contact between rotors, causing dry friction and screeching.  

Potential Causes of Oil Starvation:

Direct causes: Faulty oil separator, clogged oil cooler or lines, loose oil pipe fittings.  

Indirect causes: Malfunctioning minimum pressure valve, substandard lubricant, improper oil separator design, damaged check valve, incorrect oil return pipe installation, or excessive air demand causing low-pressure operation.  

Solution:

Check oil level, replace the oil filter, and troubleshoot faulty components.  

Ensure oil fills at least ¾ of the rotor heightbefore startup.  

Critical Note:After prolonged shutdown, refill the compressor head with oil before restarting to prevent instant oil starvation.  

3. Cause: Faulty Inlet Valve (Leakage or Vibration)

A malfunctioning inlet valve (e.g., poor sealing or check valve vibration) generates noise.  

Solution: Replace or adjust the valve.  

Valve Assembly Precautions:

1. Ensure all components are clean.  

2. Verify proper contact between valve plate and seat, radial clearance, lift, and spring specifications.  

3. Replace all internal components (valve plate, buffer, spring) simultaneously.  

4. Conduct a leak test before installation.  

4. Cause: Motor Bearing Failure  

Diagnosis & Solution:  

Use a screwdriver to listen for bearing sounds:  

Normal:Smooth, uniform rolling sound.  

Excessive play/wear:Loud rolling/vibration → Replace bearing.  

Contaminated grease:Dull, heavy sound → Clean with kerosene and relubricate.  

Irregular knocking:Broken roller → Replace bearing.  

Screeching:Insufficient lubrication or incorrect oil → Add/change oil.  

5. Cause: Rotor Assembly (Host) Issues

Foreign object ingress causing rotor jamming/screeching.  

Excessive clearance between rotors and bearings.  

Damaged main bearings.  

Solution:  

Perform a major overhaul and readjust clearances.  

Clearance Guidelines:  

Optimal clearance ratio: 0.8–1.2 µm (0.0008–0.0012 mm).  

Adjust driving-side clearance slightly larger and non-driving-side clearance smaller(ratio 1.0–1.2) for long-term reliability.  

6. Cause: Damaged Muffler System

The muffler system (chassis, brackets, panels, soundproofing foam, seals) may degrade or loosen.  

Solution:  

Inspect muffler integrity and tighten loose bolts.  

Note: Uncontrolled vibrations from gas forces, inertia, or friction can amplify noise if not properly dampened.  

This guide addresses common noise issues in screw compressors, providing targeted solutions for maintenance personnel. Proper troubleshooting ensures extended compressor lifespan and optimal operational efficiency.