What Are the Parts of an Air Compressor: Diagram of Air Compressor Parts

Dec 15, 2023

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Industrial air compressors are complex machines with lots of individual parts that work together to compress air. Here, we outline the various parts of the air compressor, including the core parts of the compression system as well as smaller and consumable parts for the air compressor. This air compressor parts list will help you understand how the compressor works and how it all fits together. 

Air Compressor Working Principles

First, let’s talk about how an air compressor works. A rotary screw compressor and a reciprocating compressor (piston compressor) each work a bit differently, but they both share some common working principles. Here are the basic working principles for an air compressor.

  1. Air Intake: All compressors start their process with the intake of ambient air. Air enters the compressor through an intake valve.
  2. Compression Phase: Depending on the type of compressor, this stage can vary.
    • Rotary Screw Compressors: Two helical screws, or rotors, rotate in opposite directions, trapping and compressing the incoming air between them.
    • Reciprocating (Piston) Compressors: The piston moves within a cylinder, decreasing its volume and compressing the air. Two-stage air compressors (or multi-stage air compressors, such as high-pressure air compressors) have an additional stage of compression to reach higher pressures (PSI).
  3. Cooling Process: As compression generates heat, the air is typically cooled between stages, especially in multi-stage compressors, to make the subsequent compression more efficient.
  4. Storing Compressed Air: Once compressed, the air enters a storage tank. This tank holds the compressed air, allowing pressure to build up.
  5. Pressure Regulation: As the tank fills, the pressure inside increases. A pressure gauge is used to monitor this. Once the pressure reaches an upper limit, the compressor stops or unloads. When the pressure drops to a predetermined lower limit as the air is used, the compressor restarts or reloads to refill the tank.

Learn more about compressed air systems: Air Compressor Basics.

Core Elements of the Air Compressor

The air compressor motor and air end are fundamental components in the operation of the entire system. They work in tandem to ensure the air is compressed efficiently and delivered to the required applications.

Air Compressor Motor

Air Compressor Motor

The air compressor motor serves as the powerhouse of the compressor system. It provides the necessary mechanical energy to drive either the air end (in rotary screw compressors) or the compressor pump (in reciprocating compressors). Motors can vary in terms of power source (electric motor or gas-powered motor), size (horsepower, or HP), and efficiency. The motor’s power is directly related to the capacity of the compressor: a larger motor can drive a compressor that produces more compressed air.

Air End (for Rotary Screw Compressors)

Air End (for Rotary Screw Compressors)

In rotary screw air compressors, the air end is where the actual compression takes place. The compression chamber consists of two interlocking rotors — one male and one female. As the rotors turn, they decrease the volume of captured air, effectively compressing it. The efficiency and reliability of the air end play a crucial role in the overall performance of the compressor. Parts of the air end in a screw compressor include:

  • Rotors (Screws): The air end contains two screws, a male rotor (drive rotor), which typically has fewer lobes, and a female rotor (driven rotor), which generally has more lobes and is driven by the male rotor. The interlocking helical rotors move in opposite directions, compressing the air between their lobes as they turn.
  • Inlet Valve: The air intake controls the intake of ambient air. It can also be modulated or completely closed when the compressor is unloaded.
  • Bearings: These support the rotors, ensuring they rotate smoothly within their housing. Typically, there are both radial and axial bearings.
  • Seals: These prevent the compressed air from escaping and also keep the lubricating oil from entering the compressed air. Shaft seals around the rotor shafts are especially important.
  • Discharge Port: Once the air is compressed within the rotors, it exits the air end through this port and moves on to the aftercooler or the air receiver tank.
  • Housing or Casing: This is the outer shell that encloses all the components of the air end. It’s designed to withstand the internal pressures and also directs the flow of air and oil within the air end.
  • Cooling System (Internal): As compression generates heat, some rotary screw compressors use internal coolers (inter-coolers), which might be part of the air end, to keep temperatures in check.

Compressor Pump (for Reciprocating Air Compressors)

Compressor Pump (for Reciprocating Air Compressors)

In reciprocating air compressors, the compressor pump functions through a piston-cylinder mechanism. The piston moves within the cylinder, drawing in ambient air and compressing it. Multi-stage air pumps have multiple cylinders that compress the air in successive stages, allowing for higher pressure. The pump, much like the air end in rotary screw compressors, is essential for the generation of compressed air, making its maintenance vital for the system’s longevity and efficient operation. Compressor pump parts include:

  • Cylinder: A chamber in which the piston moves to compress air.
  • Piston: A component that moves up and down (or back and forth) within the cylinder, creating a change in volume and thus compressing the air.
  • Valves: These are one-way valves. The intake valve allows ambient air into the cylinder when the piston is in the downstroke, and the exhaust valve lets compressed air out during the upstroke.
  • Connecting Rod: This links the piston to the crankshaft, converting the rotational motion of the crankshaft into the reciprocating motion of the piston.
  • Crankshaft: Driven by the motor, the crankshaft rotates to provide the necessary movement to the piston through the connecting rods.

Other Common Air Compressor Parts

Beyond the core components that drive the compression process, an air compressor has several other essential parts that ensure its safe and efficient operation. These components provide crucial support roles that often go unnoticed but are vital for optimal performance.

Oil Pump/Lubrication System

The lubrication system is a critical component in most air compressors, including oil-flooded rotary screw and lubricated piston compressors. The primary role of an oil pump, for compressors that have one, is to circulate lubricating compressor oil to the compressor’s various moving parts, minimizing friction, wear, and heat generation. By ensuring consistent lubrication, the oil pump helps prolong the compressor’s lifespan, prevent overheating, and maintain optimal performance. Sub-components of the lubrication system include:

  • Oil Filter: As the oil circulates, it can accumulate impurities and other debris. The oil filter cleans the oil before it’s pumped to the critical components, ensuring they receive uncontaminated lubrication.
  • Oil Cooler: As the oil moves through the compressor, it absorbs heat. The oil cooler dissipates this heat, maintaining the oil at an optimal temperature and ensuring effective lubrication and cooling of the compressor parts. Overheating can reduce the oil life and damage the compressor.
  • Air Oil Separator: In systems where the lubricating oil mixes with the compressed air, an air oil separator is crucial. It removes excess oil from the air before it’s released, ensuring clean air output and recirculating the oil back into the system.
  • Oil Sump/Reservoir: This is the holding tank for the lubricating oil. It stores the oil when not in circulation and is where the oil pump draws from to distribute lubrication throughout the compressor.
  • Oil Lines/Pipes: These are the pathways through which the oil travels, connecting various components of the lubrication system and ensuring a steady flow of oil to the parts that need it.

Pressure Gauges

Pressure Gauges

A pressure gauge on an air compressor is an essential instrument that displays the current pressure level within the system, typically measured in pounds per square inch (PSI) or bar. This gauge allows operators to monitor the compressor’s output and ensure it’s operating within the desired and safe pressure range.

Check Valve

Located between the compressor and the tank, the check valve ensures that compressed air does not flow back into the compressor once it has entered the tank. This one-way valve allows air to flow into the tank while preventing it from flowing backward, ensuring consistent pressure and operation.

Safety Pressure Relief Valve

This is a crucial safety feature. If the system pressure exceeds safe levels, the safety valve will automatically open to release excess pressure, ensuring the system doesn’t experience a dangerous overpressure situation.

Unloader Valves

The unloader valve releases trapped air between the compressor and the check valve, allowing the motor to unload or restart without resistance. It ensures a smooth start-up after the compressor reaches its cut-out pressure.

Pressure Switches

These devices monitor the pressure within the air tank. When the pressure drops below a set point, the pressure switch activates the motor to start compressing more air. Conversely, when the tank reaches its maximum pressure, the switch will turn off the motor or unload the compressor, ensuring efficiency and safety.


In belt-driven compressor models, the belts transfer power from the motor to the compressor pump or air end. Regular inspection and replacement are vital as worn belts can reduce efficiency or even break, halting compressor operation. 

(Learn more: Belt-Driven vs. Direct Drive Air Compressors.)

Air Filter

The inlet air filter cleans the incoming air before it’s compressed. This prevents dust, dirt, and other contaminants from entering and potentially damaging the system or contaminating the compressed air. Clean filters ensure longer compressor life and better air quality.

Drain Valves

Accumulated moisture and condensate need to be regularly drained from the air tank. A drain valve, which can be manual or automatic, facilitates this process, ensuring that water doesn’t build up inside the tank or lines.


Gaskets provide a seal between various compressor components, preventing air leaks and ensuring efficient operation. Over time, they can wear out or degrade, so regular checks and replacements are essential.

Vibration Pads 

To reduce noise and prevent wear and tear from constant vibrations, many compressors are mounted on vibration pads. These pads absorb and dampen vibrations, leading to quieter operation and increased component longevity. 

Reciprocating Air Compressor Parts Diagram

Reciprocating air compressors are commonly known as piston compressors. This compressor parts diagram offers a clear overview of the key components of a reciprocating compressor.

Rotary Screw Air Compressor Parts Diagram

Rotary screw air compressors are renowned for their efficiency and continuous operation capabilities. This parts diagram highlights the essential elements of the compressor.

Need Air Compressor Parts?

If you need to buy compressed air system parts, Fluid-Aire Dynamics has a large inventory of parts and consumables for your industrial air compressor or air compressor system, including compressor oil and oil filters, intake filters and inline filter cartridges, air/water separators, drain valves, belts, hoses, couplers and switches. We can help you find exactly what you need. We’re also here to support you with air compressor repair services and routine maintenance for your compressed air system.

Contact Fluid-Aire Dynamics for all your compressed air needs.

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