The indicator diagram for a reciprocating pump is defined the graph between the pressure head in the cylinder and the distance travelled by piston from inner dead centre for one complete revolution of the crank. As the maximum distance travelled by the piston is equal to the stroke length and hence the indicator diagram is a graph between pressure head and stroke length of the piston for one complete revolution. 

The pressure head is taken as ordinate and stroke length as abscissa.

Ideal Indicator Diagram:

The graph between pressure head in the cylinder and the stroke length of piston for one complete revolution of the crank under ideal conditions is known as ideal indicator diagram.

Line EF represents the atmospheric pressure head equal to 10.3 meters of water.

Let 𝐻 = Atmospheric pressure head = 10.3 m of water

L = Length of the stroke

hs = Suction head and

hd = Delivery head

Ideal Indicator Diagram

Ideal Indicator Diagram

Substituting this value in equation (1), we get

Work done by pump is directly proportional to the Area of Indicator diagram

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