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in the outlet manifold is equal to or slightly greater than the condenser pressure. The
purpose of the manifolds is to provide stable inlet and outlet pressures for the smooth
operation of the valves and also provide a space for mounting the valves.
Reciprocating can be either stationary or portable, can be single or multi-staged, and
can be driven by electric motors or internal combustion engines.
Small reciprocating compressors from 5 to 30kW are commonly seen in automotive
applications and are typically for intermittent duty. Larger reciprocating compressors
well over 750 kW are commonly found in large industrial and petroleum applications.
Discharge pressures can range from low pressure to very high pressure (180 MPa).
In certain applications, such as air compression, multi-stage double-acting compressors
are said to be the most efficient compressors available, and are typically larger, and
more costly than comparable rotary units.
Household, home workshop, and smaller job site compressors are typically
reciprocating compressors 1kW or less with an attached receiver tank.
Reciprocating compressors are often used with air reservoirs to provide compressed
air for industrial and civil duties driving air tools etc. Reservoirs have to be used
because reciprocating compressors provide a pulsating air delivery.
The figure 5.1 shows a hypothetical indicator diagram for a single stage-single
acting reciprocating compressor:
a – 1 air is drawn into the cylinder on the suction stroke;
n
1 – 3 the suction valve is closed and air is compressed according to the law PV =
const;
3 – b the delivery valve opens and air is delivered under pressure;
b – a the delivery valve closes and the suction valve opens.

The cycles shown is assumed to follow a series of equilibrium states and the gas is
assumed to follow the equation of state - PV = RmT.
The theoretical work done on the air per cycle is the area enclosed by [ a-1-3-b- a ]
which equals

 k 1 
p 2
n   P  k 
W  vdp  P v  2  1
n  n 1 1 1   P   ,
1 p  1 
 


P
where   2
P
1

The theoretical work when air is
compressed at isentropic process [1-2]
k
according to the law PV = cons equals

n
k
1-2 - PV =const; 1-3 – PV =const; 1-4-PV = const; p 2 k k 1
Fig. 5.3 - A hypothetical indicator diagram for a W  vdp  P v    k 1 


acting reciprocating compressor k k 1 1 1  


1 p
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