A pressure volume diagram is used to describe corresponding changes in volume and pressure in a system. They are commonly used in thermodynamics, cardiovascular physiology and respiratory physiology.
PV diagrams were originally called indicator diagrams. They were developed in the 18th century as tools for understanding the efficiency of steam engines. It was developed by James Watt and John Southern.
PV diagrams can be used to estimate the net work performed by a thermodynamic cycle. The net work is the area enclosed by the PV curve in the diagram. This usage derived from the development of indicator diagrams which were used to estimate the performance of a steam engine. The diagram records the pressure of steam versus the volume of steam in a cylinder throughout a piston’s cycle of motion in a steam engine.
On a pressure volume diagram, the volume is on the x-axis and the pressure is on the y-axis.