Practical Fault Diagnosis – Overheating, Abnormal Noises, and Leakage

This article systematically analyzes three common categories of compressor faults: component overheating, abnormal noises, and leakage. By summarizing symptoms, tracing causes, and detailing solutions, it provides a clear diagnostic and corrective framework for operations and maintenance personnel.

I. Diagnosis and Rectification of Component Overheating

(A) Cylinder Overheating

A continuously rising cylinder temperature is a common compressor fault, primarily rooted in issues with the cooling and lubrication systems.

Primary Causes:

    1.  Cooling Failure: Insufficient or interrupted cooling water in the water jacket or cylinder head.

    2.  Poor Interstage Cooling: Overheating of a second-stage cylinder is often due to an intercooler being short of water or having low efficiency, preventing effective cooling of the first-stage discharge.

    3.  Increased Thermal Resistance: Excessive deposits in the water jacket or clogged cooling tubes, impairing heat transfer.

    4.  Abnormal Friction: Misaligned piston assembly within the cylinder, increasing frictional heat; or lack of oil causing dry friction.

    5.  Incorrect Clearance:

        Clearance Too Small: Leads to excessively high compression ratios at top/bottom dead center, exacerbating temperature rise.

        Clearance Too Large: Excessive residual high-pressure gas raises the starting temperature for compression.

    6.  High Intake Gas Temperature.

    7.  Internal Leakage: Exhaust valve leakage allows high-temperature gas to escape.

    8.  Mechanical Alignment Issues: A bent piston rod causes the piston to tilt within the cylinder, creating localized intense friction.

Rectification Methods:

    1.  Ensure Adequate Cooling: Increase flow if water supply is insufficient; immediately shut down the compressor if cooling water flow is interrupted.

    2.  Clean the System: Remove scale and deposits from the cylinder, liner, and cooler.

    3.  Optimize Lubrication: Inspect and adjust the oil supply from the lubrication system.

    4.  Adjust Clearance: Set the cylinder clearance volume to the specified standard.

    5.  Correct Alignment: Align the piston assembly concentrically with the cylinder; repair or replace a bent piston rod.

    6.  Control Intake: Implement measures to lower the temperature of the intake gas.

    7.  Repair the Valves: Identify the faulty valve and replace its components such as valve plates and springs.

(B) Piston Rod Overheating

Primary Causes:

    1.  Assembly Issues: Excessive clearance with the packing, or misalignment during assembly.

    2.  Poor Surface Finish: Rough surface on the piston rod.

    3.  Poor Lubrication: Contaminated or insufficient lubricating oil leading to dry friction.

    4.  Contamination: Foreign matter entering the packing chamber via gas or oil.

    5.  Component Seizing: Metal sealing rings in the packing box unable to move freely.

    6.  Insufficient Cooling: Poor cooling performance in packing boxes equipped with cooling devices.

    7.  Incorrect Installation: Tilted installation of the packing box, causing non-parallel movement of the piston rod.

Rectification Methods:

    1.  Reassemble: Adjust the clearance between the piston rod and packing, ensuring proper alignment.

    2.  Refinish Surface: Reinstall precisely and regrind the piston rod.

    3.  Improve Lubrication: Clean the system, replace with clean lubricating oil, and adjust oil quantity.

    4.  Maintain Cleanliness: Ensure the gas and oil entering the packing chamber are clean.

    5.  Check Mobility: Test the sealing rings during installation to ensure free movement with proper clearance.

    6.  Enhance Cooling: Inspect and improve the cooling condition of the packing box.

    7.  Correct Installation: Re-inspect and correct the installation posture of the packing box.

(C) Bearing Overheating

Primary Causes:

    1.  Poor Contact: Uneven contact and excessive unit pressure between the bearing and journal, common after new machine commissioning or bearing replacement.

    2.  Alignment Issues: Bearing misalignment, or a bent/twisted crankshaft.

    3.  Lubrication System Fault: Poor-quality bearing shells, incorrect lubricant viscosity, clogged oil passages, low oil pump pressure, or interrupted oil supply.

    4.  Contamination and Overfilling: Foreign matter in the bearing, or excessive/contaminated lubricating oil.

    5.  Abnormal Wear: Uneven, excessive wear of the bearing shell.

    6.  Installation Error: Misalignment between the compressor and prime mover (motor/diesel engine) couplings.

Rectification Methods:

    1.  Scrape and Fit: Use the spotting (bluing) method to scrape the bearing shells, increasing the contact area and reducing unit pressure.

    2.  Adjust and Correct: Adjust the clearance; inspect, correct, or replace a bent crankshaft.

    3.  Ensure Proper Oil and Pressure: Use qualified bearing shells and lubricating oil; inspect and clean oil passages; adjust the oil pump to specified pressure.

    4.  Clean and Change Oil: Clean the bearings and replace with fresh oil; adjust oil pressure.

    5.  Replace Bearing Shells.

    6.  Precise Alignment: Strictly align the compressor with the prime mover per manual specifications, especially for rigid couplings.

(D) High System Oil Temperature

Primary Causes:

    1.  Poor quality or contaminated lubricating oil.

    2.  Excessively tight assembly clearances in the running gear (crosshead, connecting rod, bearings, etc.), or embedded hard metal particles.

    3.  Poor combined clearances at various lubrication points.

    4.  Lubricating oil viscosity unsuitable for the machine.

    5.  Excessive scale in the cooling water tubes of the oil cooler, causing blockage and poor cooling.

Rectification Methods:

    1.  Replace with lubricating oil meeting specifications.

    2.  Readjust running gear clearances to standard, paying attention to assembly cleanliness.

    3.  Adjust clearances at all lubrication points to specified values.

    4.  Clean the oil cooler; increase cooling water flow if insufficient.

II. Diagnosis and Rectification of Abnormal Noises

Abnormal noises are crucial signals of internal compressor faults and should be diagnosed based on sound characteristics and location.

(A) Frame Knocking (Reflected on the Entire Machine Frame)

Causes: Primarily due to excessive clearance in moving pairs or loose connections.

    1.  Excessive clearance in main bearings, connecting rod big/small end bearings, or crosshead bearings.

    2.  Loose shrink-fit of crosshead bearings or connecting rod small-end bearings.

    3.  Loose connections such as through-bolts, piston rod nuts, piston nuts, crankshaft couplings.

    4.  Worn arc surface of the crosshead shoe, leading to excessive clearance.

Rectification Methods:

    Replace and Adjust: Replace relevant bearings and adjust clearance to manual specifications.

    Tighten and Secure: Tighten all loose bolts and nuts; secure lock washers properly.

    Repair Wear: Re-plate crankshaft journal areas to restore interference fit; use bushings or scrape and repair the crosshead shoe arc surface to adjust clearance.

(B) Cylinder-Related Knocking

    1.  Knocking in Individual Cylinder(s) Associated with Frame:

        Causes: Piston ring scraping cylinder, insufficient piston clearance, loose piston nut, foreign object entering cylinder, poor condensate drainage causing water hammer, improperly installed liner or packing.

    2.  Knocking Inside Cylinder:

        Causes are more diverse and complex, including besides the above: worn/stuck/broken piston (rings), worn cylinder (liner), misalignment between crank-connecting rod mechanism and cylinder, bent piston rod, excessive cylinder clearance, too much oil or water in gas causing water hammer, poor cooling leading to oil coking, water leakage from cylinder water jacket, malfunctioning inlet/exhaust valves, loose components in valve unloader devices, damaged packing, etc.

Rectification Methods:

    Targeted Action: Take corresponding measures based on diagnosed cause, such as adjusting clearance, tightening nuts, removing foreign objects, improving drainage, replacing damaged piston rings, liners, packing, or valves.

    Systematic Overhaul: For complex causes, conduct systematic inspection including straightening piston rod, aligning mechanism, repairing water jacket leaks, servicing valve devices, etc.

(C) Other Characteristic Abnormal Noises

    1.  Moving Parts Knocking:

        Causes: Loose or broken fasteners like connecting rod bolts, bearing bolts, crosshead nuts; excessive clearance in various bearings; poor contact between bearing shell and housing; loose fit between crankshaft and coupling.

        Rectify: Tighten or replace damaged parts; adjust clearance; scrape bearing shell backs; re-plate crankshaft or replace coupling.

    2.  Shrill Knocking Inside Frame:

        Causes: Crosshead or bearing wear exceeding limits; worn or loose crosshead pin; loose connection between piston rod and crosshead; flywheel runout.

        Rectify: Replace bearings; inspect and tighten crosshead pin and piston rod connection bolts; correct or reinstall flywheel.

    3.  Abnormal Noise in Suction Valve Chamber:

        Causes: Impact sound from valve plate stopping, leakage noise from valves, airflow noise from improper unloader operation.

        Rectify: Correct or replace valve plates; correctly install valve assemblies; adjust the unloader device.

    4.  Noise Inside Bearing Housing:

        Causes: Excessive clearance between bearing shell and journal; oval wear of both; improper shimming or loose fastening screws.

        Rectify: Adjust clearance; repair or replace bearing shell/journal (e.g., chrome plating and grinding); adjust shims and tighten screws.

III. Diagnosis and Rectification of Leakage and Wear Faults

(A) Packing Gland Leakage

    1.  Excessive Gas Leakage:

        Causes: Insufficient oil supply; incorrect assembly sequence or poor lapping; scratches on piston rod; incomplete tightening; non-parallel piston rod movement; packing not gripping tightly.

        Rectify: Increase oil supply; carefully lap and assemble in correct sequence; repair or super-finish piston rod; tighten adequately and adjust alignment.

    2. Oil Leakage:

        Causes: Broken tension springs; worn piston rod; scratches on piston rod or sealing rings; sealing rings worn to zero clearance.

        Rectify: Replace springs, piston rod, or sealing rings.

    3.  Abnormal Wear or Burning:

        Causes: High gas leakage rate; insufficient axial clearance; poor assembly; rough piston rod; poor lapping; insufficient oil supply; contaminants in gas/oil.

        Rectify: Reduce leakage; assemble per drawings; lap correctly; repair piston rod; increase supply of clean lubricating oil.

(B) Abnormal Piston Ring Wear or Burning

Primary Causes:

    1.  Substandard piston ring material or tension, or rough cylinder liner surface.

    2.  Condensate mixing in,destroy the oil film.

    3.  Insufficient lubricating oil quantity or poor quality.

    4.  Contaminants in the gas.

    5.  Cylinder scoring.

    6.  Substandard piston ring grooves or insufficient working (hot) end gap of piston rings.

Rectification Methods: Use qualified parts; thoroughly separate condensate; ensure adequate supply of quality lubricant; enhance gas filtration; overhaul or replace cylinder/piston; adjust piston ring hot gap.

(C) Premature Valve Plate Failure

Primary Causes:

    1.  Substandard valve plate material, heat treatment, or machining.

    2.  Damaged sealing surface or excessive lift.

    3.  Contaminants in the intake gas.

    4.  Condensate or excessive oil entering the valve chamber.

    5.  Worn valve guide surface causing abnormal valve plate motion.

Rectification Methods: Replace with qualified valve plates; lap or replace valve plates and seats; clean intake piping; remove condensate and control oil ingress; replace valve seat.

(D) Oil Pressure System Faults

1.  Gradual Oil Pressure Drop:

    Causes (14 points): Involves rising oil temperature, clogged filter, air leaks/blockages in lines, air ingress/pump wear/low pump speed, thin/watery oil, malfunctioning relief/other valves, line rupture, worn bearings, faulty pressure gauge, insufficient oil, etc.

    Rectify: Systematically inspect, clean, repair, or replace faulty components; ensure seals are tight; use appropriate oil and maintain oil level.

2.  Oil Pump Failure to Deliver Oil:

    Causes (7 points): Pump assembly/rotation issues, air leaks at housing/lines, clogged suction pipe, leaking pump packing, clogged filter/check valve, insufficient oil.

    Rectify: Inspect and repair pump, clean related components, bleed air, maintain oil level.

IV. Abnormal Frame Vibration

Primary Causes:

    1.  Excessive clearance in moving pairs like bearings, crosshead, and shoes.

    2.  Severe vibration originating from the cylinder section itself transmitting to the frame.

    3.  Poor connection at mechanical joint surfaces, loose foundation bolts.

    4.  Misalignment between the compressor and drive motor.

Rectification Methods:

    Replace bearings and adjust clearance to standard.

    Strengthen the support rigidity of the cylinder section.

    Thoroughly inspect and tighten all foundation bolts.

    Realign and adjust the concentricity of the compressor and motor.