There are several main types of air compressors. Reciprocating compressors use pistons moving up and down to compress air. Rotary screw compressors use two rotating screws to compress air. Rotary scroll compressors use an orbiting scroll to compress air with fewer moving parts than rotary screw compressors. Rotary vane compressors use rotating vanes inside a chamber to compress air. Centrifugal compressors use an impeller to increase air velocity and pressure. Rocking piston compressors use a reciprocating piston and connecting rod to compress air. Compressors also differ based on their lubrication method and drive type.

1. TYPES OF AIR
COMPRESSOR
S
By Pramod A

2. Reciprocating Air Compressors
Reciprocating and piston air compressors are
interchangeable terms, and this type of air
compressor is the most common on the market
today. They take advantage of the principle of
positive displacement. When the piston moves
down inside the cylinder, the air enters the space
above thanks to the difference between the
atmospheric pressure and the pressure inside the
cylinder. The air is then compressed as the piston
moves upwards. These are known as single-
stage compressors.

3. Two-stage compressors take the air in from the
atmosphere just like single-stage units, but as you
can see on the picture they have two cylinders
instead of one.
During the first stage, the air is compressed to an
intermediate pressure. After that the majority of
heat is removed, and the air is passed on to
another cylinder where it is compressed to a
specified value.

4. Rotary Screw Air Compressors
This type of compressor has two mated helical
screws located inside a chamber. As each of the
two screws rotates, the air pressure inside the
chamber is increased which effectively reduces
the volume of air. However there is a drawback
to this mechanism.

5. This type of functionality creates a lot of friction and
heat which means you have to cool the whole
system down in an efficient manner in order to keep
operation smooth. For this purpose lubrication is
used however, do bear in mind that oil has to be
separated from the compressed air before it can be
used.

6. Rotary Scroll Air Compressors
This solution features fewer moving parts than the rotary
screw approach. Basically, with rotary scroll compressors
the compression within a scroll is carried out via the
interaction of a fixed and an orbiting helical element which
gradually compresses the air that’s drawn in. As a result
of this continuously repeated process you get pulsation-
free compressed air.
This type of design may feature either splash lubrication,
or an oil free design.

7. Rotary Sliding Vane Air
Compressors
This type of compressor has a motor that consists
of a rotor, stator, and blades. On one end there is
an intake port, and on the other an exhaust port.
The stator is located between the two and also
contains the rotor. The turning of the rotor
increases the volume on the intake end, and
decreases it on the exhaust end.

8. The blades or vanes move outward and remain in
place against the walls of the stator thanks to rotational
acceleration. Lubricant is also used to reduce friction
as well as to plug up any potential leaks. As is the case
with rotational screw compressors, the air and oil need
to be separated first.

9. Centrifugal Air Compressors
Unlike all the previous types of compressor, a
centrifugal air compressor is not based on the
principle of positive displacement. Instead, the
principle they are based on is called dynamic
compression. What this does is increase air
pressure by raising the velocity. These
compressors have an impeller that is able to rotate
up to 60,000 times per minute.

10. The air molecules are sped up first, and then
slowed down with the help of a diffuser. In order
to pull this off, centrifugal compressors have
intercoolers which cool the air and remove any
fluid that builds up in the process (since
moisture can harm the motor).

11. Rocking Piston Compressors
Rocking piston compressors are a variation of
the standard piston-type unit although in this
case, the air pressure is increased through a
reciprocating interaction of a connecting rod and
piston.

12. Since the pistons on these compressors have
non-metallic rings they don’t need splash
lubrication. Another characteristic of these is
they are smaller and deliver lower pressure
values.

13. Classification of Air
Compressors based on the
type of Lubrication they use

14. Oil-Free Compressors
Oil-free compressors don’t require a lubricant in
order to function. Instead, they have permanently
oiled bearings. These compressors are
convenient because they require very little
maintenance, but they also have other
advantages. They are capable of operating in
low temperatures and on uneven terrain. On the
flip side they have a tendency to heat up more,
and are generally less suitable for heavy duty
work.

15. Splash-Lubricated Compressors
Splash lubrication employs an oil dipper found on the
bottom of the connecting rod which dips into the oil
bath, and splashes the oil onto the mechanical parts
and bearings to reduce friction. Overall, this is the most
common type of lubrication among piston-type
compressors. They experience a lot less wear and tear
than oil-free designs, and tend to heat up less. But their
performance is questionable on uneven surfaces, and
they do require proper maintenance (although they are
better suited to heavy-duty applications).

16. Pressure Lubrication Compressors
This type of compressor features an oil pump
which supplies the oil to all crucial segments of
the compressor with the help of a crankshaft,
cylinder walls and the piston bearing. This
system is extremely efficient, but it does costs
more money.

17. Classification of Air
Compressors based on the
type of Drive they use

18. Direct Drive Compressors
Compact portable oil-free compressors usually
fall into this category since a direct drive is
relatively small and requires minimal
maintenance.

19. Compressors can either be flange-mounted or
direct-coupled to the power source. Another
benefit of direct drive compressors is their ability
to deliver compressed air directly without filling
the air tank first.

20. Belt Drive Compressors
Both gas and electric compressors employ a belt
drive because it offers better flexibility in order to
match the compressor load to a power source at
the lowest possible price. However, in order to
ensure the safety of the operator belts must have
some sort of protective cover.