Lifeblood of Operation – Lubrication, Cooling, and Instrument Monitoring

I. What Causes Excessive Lubricating Oil Consumption in Compressors?

Excessive lubricating oil consumption in compressors is primarily caused by the following factors:

    1.  Unsuitable Oil Viscosity: Oil temperature is too high, thinning the oil, or the lubricant grade used does not meet requirements.

    2.  Excessive Oil Pressure: The lubrication system pressure is set too high, forcing excessive oil into areas like the cylinders.

    3.  Excessive Piston-to-Cylinder Clearance: Excessive wear leads to clearance beyond specification, allowing oil to pass into the cylinder.

    4.  Cylinder Out-of-Round or Severe Wear: Loss of shape precision on the cylinder inner wall reduces sealing effectiveness.

    5.  Oil Carry-Over into Cylinder:

        Piston rings are excessively worn and have lost their elasticity.

        Piston rings are stuck (seized) in their grooves and cannot tension properly.

        Excessive side or back clearance between the piston rings and their grooves.

        Incorrect piston ring installation (e.g., order, orientation).

    6.  Excessive Bearing Clearance: Wear in crankshaft or connecting rod bearings leads to increased clearance and oil loss.

    7.  High Crankcase Temperature or Poor Ventilation: High temperatures increase oil evaporation; poor ventilation prevents effective separation and recovery of oil mist.

    8.  Splash Lubrication System Issues: The splash rod is too long or the crankcase oil level is too high, causing excessive oil to be splashed onto the cylinder walls.

II. Why Can't the Same Grade of Lubricating Oil Be Used in Winter and Summer in Compressors?

A general characteristic of lubricating oils is that viscosity decreases as temperature rises and increases as temperature falls. Therefore, compressors require lubricating oils of appropriate viscosity selected according to different seasons (primarily summer and winter), i.e., different ambient and operating temperatures.

In the Chinese lubricant grading system, a higher number indicates higher viscosity. Therefore, when conditions permit, different oil grades should be used in winter and summer. General recommendations are:

    Cylinder and Packing Gland Section: Use No. 19 compressor oil in summer and No. 18 compressor oil in winter.

    Crankshaft-Connecting Rod Mechanism Section: Use No. 50 machine oil in summer and No. 30 or No. 40 machine oil in winter.

For general small single-acting compressors, No. 13 compressor oil can be used in winter and No. 19 in summer. Correct oil selection ensures the compressor receives adequate lubrication under different temperature conditions.

III. What Lubrication Methods Are Used in Compressors?

Depending on the compressor's structural characteristics, the following primary lubrication methods are employed:

    1.  Forced-Feed (Pressure) Lubrication: Uses mechanical devices like oil pumps or force-feed lubricators to deliver oil under pressure to points requiring lubrication. This method provides reliable lubrication with adjustable oil feed and is widely used in large and medium-sized compressors with crossheads.

    2.  Splash Lubrication: Relies on a splash rod attached to the connecting rod (or the rotation of the crankshaft) to fling oil from the crankcase onto various friction surfaces. This method is simple in construction, but the cylinder and running gear must use the same oil, the oil level must be strictly controlled, and oil filtration is difficult. Commonly used in small compressors without crossheads.

    3.  Injection Lubrication: Oil is injected as a mist into the cylinder or compression chamber, distributing it with the gas flow to lubrication points. Used in ultra-high-pressure compressors, sliding vane compressors, and screw compressors, etc.

    4.  Drip-Feed Lubrication: Delivers oil via oil cups, wicks, and feed lines by dripping to components requiring lubrication, or by periodic manual oiling with an oil can. Suitable for low speed, lightly loaded auxiliary components.

    5.  Oil-Ring Lubrication: Uses an oil ring loosely fitted on a shaft journal; rotation carries oil from the sump into the bearing for circulation. Often used for rolling element bearings or some plain bearings.

IV. Why Does Lubricating Oil Need to Be Changed Periodically?

After a certain period of use, lubricating oil quality degrades due to the following factors, necessitating periodic change:

    1.  Metal particles (wear debris) from friction surfaces.

    2.  Hard particles like dust introduced with intake air.

    3.  Residual molding sand not thoroughly cleaned from castings.

    4.  Flaking paint from component surfaces.

    5.  Water ingress during the cooling process, leading to emulsification and degradation.

    6.  Gradual deterioration of lubricating properties due to temperature and other conditions during circulation.

These contaminants can form an abrasive "lapping compound" in the oil, accelerating wear on machine friction surfaces. Oil should be changed when its performance deteriorates to specified limits.

If testing equipment is unavailable, it is generally recommended to change the oil every 2000~3000 hours of operation, thoroughly cleaning the oil supply system and all lubrication points simultaneously.

V. Which Instruments Should Be Checked Regularly on a Compressor?

Regular instrument checks are key to assessing compressor performance. In addition to daily operational monitoring instruments, the following should be used periodically:

    1.  Tachometer: Measures the actual speed of the compressor, diesel engine, or motor.

    2.  Stopwatch: For precise time measurement, used in efficiency calculations, etc.

    3.  Master/Calibration Pressure Gauge: Used to verify the accuracy of working pressure gauges, ensuring correct pressure readings.

    4.  Flow Meter: Measures the actual gas flow rate, directly assessing discharge capacity.

Calculating and analyzing data from these instruments allows for a scientific evaluation of the compressor's operating condition and performance level.

VI. What Causes Failure to Meet Designed Discharge Capacity and How Is It Resolved?

Common Causes of Insufficient Discharge Capacity:

    1.  Insufficient Drive Power: The output horsepower of the diesel engine or electric motor is inadequate.

    2.  Prime Mover Speed Reduction:

        Malfunction of the diesel engine governor.

        Clutch slippage in portable compressors.

    3.  Valve Malfunctions: Broken valve springs, cracked or warped valve plates.

    4.  System Leaks: Leakage from the intercooler and gas piping.

    5.  Packing Gland Leakage.

    6.  Clogged Intake Air Filter.

    7.  Excessive Piston Ring Wear.

    8.  Excessive Clearance Volume in the First-Stage Cylinder.

    9.  Damaged Sealing Gaskets: Cylinder head gasket, valve gasket, or cylinder head internal seal ring damage.

    10. Poor Valve Seat Sealing: Foreign material ingress or valve plate deformation.

    11. Unloader Valve Fault: Spring damage, or unloader pin holding the inlet valve open due to a loose push rod nut.

Corresponding Troubleshooting Methods:

    1.  Inspect and adjust the diesel engine or electric motor to ensure rated power output.

    2.  Repair and adjust the governor and/or clutch.

    3.  Replace damaged valve plates or springs.

    4.  Inspect and tighten all connecting rod bolts.

    5.  Inspect packing gland sealing and repair.

    6.  Clean or replace the filter element.

    7.  Install new piston rings.

    8.  Adjust cylinder clearance volume to the design value.

    9.  Replace damaged gaskets or seal rings and ensure proper sealing.

    10. Remove foreign material from valve seats, or lap/replace valve plates and seats.

    11. Replace the unloader valve spring and repair/adjust the unloader.

VII. What Hazards Are Caused by Compressor Vibration?

Excessive compressor vibration leads to a series of hazards:

    1.  Increased Energy Consumption: Vibration itself consumes energy, reducing operational efficiency.

    2.  Instrument Damage: Can cause control instruments to malfunction or be damaged, affecting monitoring and safety.

    3.  Accelerated Wear: Increases wear on mating friction surfaces.

    4.  Induces Serious Failures: May lead to catastrophic events like cylinder scoring or bearing seizure.

    5.  Damages Piping Systems: Can cause pipe cracking, loosening of flange connections, leading to leaks.

    6.  Deteriorates Working Environment: Increases noise levels, harming operator health.

    7.  Shortens Machine Life: Long-term vibration induces metal fatigue, reducing the compressor's overall service life.

VIII. How Is Compressor Vibration Eliminated?

Mitigating compressor vibration typically requires addressing the following areas:

    1.  Balance Correction: Perform strict static and dynamic balance checks on rotating and reciprocating components (e.g., crankshaft, connecting rods, piston) to eliminate inherent imbalance.

    2.  Alignment: Ensure precise alignment between the compressor and its driver (motor/diesel engine).

    3.  Foundation Design/Construction: The foundation must be constructed strictly according to design dr awings, and there must be no rigid connection between the foundation and any building structure; vibration isolation measures should be applied.

    4.  Piping Support: For vibration induced by gas pulsation, all associated piping and equipment must have secure supports and clamps. Cantilevered brackets require reinforced supports and should be shimmed tightly.

    5.  Foundation Bolts: The tightening torque for all foundation bolts should be uniform.

    6.  Ensure Rigidity: The compressor frame (bedplate) must possess sufficient structural stiffness.

IX. What Faults Occur in Intercoolers and How Are They Rectified?

Common Intercooler Faults:

    1.  Low Cooling Efficiency: Inlet cooling water temperature is too high (generally requiring outlet gas temperature not to exceed 140~160°C).

    2.  Poor Heat Transfer: Scaling on the outside of cooling tubes, oil fouling on the inside or outside, severely impeding heat conduction.

    3.  Reduced Water Flow: Damage to internal baffle plates, causing water flow short-circuiting.

    4.  Tube Damage: Cooling water tube rupture or cracking due to freezing.

Troubleshooting Methods:

    1.  Adjust Water Temperature/Flow: Control inlet water temperature within specified limits; increase cooling water flow during hot seasons.

    2.  Clean Descaling: Periodically inspect and clean scale and oil fouling from the intercooler.

    3.  Repair Baffles: Repair or replace damaged flow baffles.

    4.  Repair Tubes: Patch-weld or replace ruptured or frozen/cracked cooling tubes.

X. What Causes a Drop in Intercooler Pressure and How Is It Fixed?

Causes of Intercooler Pressure Drop:

    1.  First-Stage Valve Leakage: Damaged valve plates, broken springs, or foreign material between the valve plate and seat in the first-stage discharge or intake valves, causing gas backflow or leakage.

    2.  Intercooler Body Leakage: Poor sealing of the intercooler upper/lower covers, or ruptured cooling tubes, causing gas leakage.

    3.  Connection Point Leakage: Leaks at piping connections or pressure gauge fittings connected to the intercooler.

Troubleshooting Methods:

    1.  Inspect Valves: Disassemble and inspect first-stage intake and discharge valves, replace damaged plates/springs, and remove foreign material.

    2.  Inspect Intercooler: Perform a pressure leak test on the intercooler, patch or replace damaged tubes, tighten or replace seals/gaskets.

    3.  Check External Connections: Carefully inspect and tighten all piping and connections, eliminating leaks.