What is Piston Air Compressors?

Piston or reciprocating (oil lubricated) air compressors are single-acting, air-cooled air compressors. These piston air compressors are furnished as compact, self-contained, air receiver tank mounted units that are automatically regulated and driven by an electric motor or diesel engine. An air-cooled aftercooler, low oil level shutdown switch and automatic drain valve are among the optional accessories that can be provided.

These piston air compressors may be used for a variety of compressed air application. Application of these air compressors as either a primary or supplementary source of air is virtually unlimited in industrial plants, service stations and auto repair shops. Supplementary service includes such uses as furnishing air at pressure not carried in regular shop lines, air at isolated locations, and standby service for air when larger air compressors are shut down.

Basic Operation

The basic principle of operation is as follows On the suction stroke of the first-stage piston(s), air at atmospheric pressure enters the cylinders through the inlet filter(s) and then the inlet valves located in the head. On the compression stroke of the first-stage piston(s), the air is compressed to an intermediate pressure and discharged through the discharge valves(s) into common manifold(s). From the manifold(s) the air passed through the intercooler tubes, where the heat of first-stage compression is removed.

On the suction stroke of the second-stage piston this cooled air enters the second-stage cylinder through the inlet valve. The compression stroke of the second-stage piston compresses the air to the final discharge pressure and forces it out through the discharge valve into the receiver tank or system. If cooling of the discharge air is required, an air-cooled aftercooler should be installed between the air compressor discharge and the receiver tank or system.

Installation Location

For most electric motor units, select a relatively clean and dry well-lighted indoor area with plenty of space for proper ventilation, cooling airflow and accessibility. Provide 1,000 cubic feet of fresh air per 5 horsepower. Locate the unit at least 50 cm from walls, and make sure the main power supply is clearly identified and accessible.

Unless the electrical components of the unit are specially protected for outdoor use, do not install an electric motor unit outdoors or in an area that will expose the electrical components to rain, snow or sources of appreciable moisture.


In frequently humid areas, moisture may form in the pump and produce sludge in the lubricant, causing running parts to wear out prematurely. Excessive moisture is especially likely to occur if the unit is located in an unheated area that is subject to large temperature changes.

Two signs of excessive humidity are external condensation on the pump when it cools down and a “milky” appearance in petroleum lubricant.

You may be able to prevent moisture from forming in the pump by increasing ventilation, operating for longer intervals or installing an external crankcase heater kit.


Consult local officials for information regarding acceptable noise levels in your area. To reduce excessive noise, use vibration isolator pads or intake silencers, relocate the unit or construct total enclosures or baffle walls.

Note: Condensate

All compressed air systems generate condensate which accumulates in any drain point (e.g. tanks,filters, drip legs, aftercoolers, dryers). This condensate contains lubricating oil and/or substances which may be regulated and must be disposed of in accordance with local, state, and federal laws and regulations.

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