Compressors: lubrication, cooling and the preventive plan

In one line

In a compressor, lubrication and cooling are not just two more preventive maintenance tasks: they are the two factors that most determine how long the machine lasts and how much energy it consumes.

What they are

Compressors raise the pressure of a gas. They are classified into two large families: reciprocating (piston-based) and rotary (screw or another rotating mechanism). Both share the same two critical points — lubrication and cooling — although their specific maintenance plan differs.

Lubrication system

In the manual's own words, this is the most important chapter in the machine's life: proper lubrication, with a good-quality oil suited to compressors, considerably extends its service life. Before startup it is essential to check the crankcase oil level — and that level is always checked hot and with the machine stopped, kept between the maximum and minimum marks.

The three main characteristics that define whether an oil is the right one are viscosity, freezing point and flash point.

Cooling system

Insufficient cooling matters for two reasons at once: it causes the typical overheating problems and it also increases energy consumption. Small compressors are air-cooled; large ones are water-cooled, which is more effective.

Keeping the compressor clean is part of cooling, not a separate issue: dirt acts as a very effective insulator, so the inlet and outlet temperatures of the cooling fluid (water or air) need to be checked daily. When the compressor is large enough, its cooling heat can be reused as heating for the plant or offices — one of the most widely used energy-recovery setups for this type of equipment, and one of the most profitable.

Preventive plan for reciprocating compressors

| Task | Frequency | |---|---| | Check the oil level | Daily | | Check the cylinder head covers | Daily | | Change the intake filter | Every ~1,000 h | | Check the safety devices | Daily | | Check instrumentation operation | Daily | | Check the oil filter | Every ~1,000 h | | Change the crankcase oil and oil filter | Every ~2,000 h | | Check the electrical equipment and motor connections | Every ~2,000 h | | Check the regulation | Every ~1,000 h | | Inspect and clean the valves | Every ~2,000 h |

Preventive maintenance for rotary compressors

The tasks differ from the reciprocating compressor's because the mechanism is different too — there are no valves to clean here, but there is a belt and a more extensive cartridge-based filtering system:

• Check the oil level
• Change the oil
• Change the oil filter cartridge
• Change the oil separator filter cartridge
• Change the air filter cartridge
• Check the oil filter
• Tighten the belt
• Change the belt
• Clean the air/oil radiator
• Drain the condensate
• Clean the anti-dust pre-filter

How often each one is done depends on the model and manufacturer — unlike the reciprocating compressor, which follows fairly standardized hour-based frequencies, the rotary compressor usually comes with its own intervals in the equipment's manual.

What it is for

Separating lubrication and cooling from the rest of the preventive plan helps prioritize: if a compressor can only be checked with limited frequency, the oil level (hot, stopped) and the coolant temperature are the two checks that should never be skipped, because they are the ones that most quickly turn a lapse into an unplanned stoppage.

Benefits

• The frequency table for reciprocating compressors gives a concrete starting point in hours, not a vague sense of "every so often"
• Reusing the cooling heat of large compressors cuts the plant's heating energy cost, on top of taking better care of the equipment
• Telling reciprocating apart from rotary avoids applying one's maintenance plan to the other, since they have different mechanisms and different weak points

Limitations to keep in mind

• The frequencies in the table are a general reference: each compressor manufacturer's manual may adjust them by model and operating conditions
• This manual's rotary compressor plan does not come with its own frequencies — they need to be filled in from the actual equipment's technical sheet
• No preventive maintenance table replaces the daily check of temperatures and oil level, which is what catches a problem between one scheduled review and the next

In summary

Lubrication and cooling are not two maintenance tasks among many: they are the two factors that most decide a compressor's service life and energy consumption. The preventive table for reciprocating compressors gives concrete frequencies in hours; for rotary compressors, the task list follows the same idea but with each manufacturer's own intervals.