In mechanics, a diaphragm is a sheet of a semi-flexible material anchored at its periphery and most often round in shape.
The increase and decrease in volume caused by the action of the diaphragm alternately forces fluid out the chamber and draws more fluid in from its source.
It is favored in certain applications due to its high durability and reliability.
This comes with a downside, as the vessel needs to be replaced in the case of a rupture of the diaphragm.
[2] Diaphragm tanks are used to store hypergolic propellant aboard space probes and various other spacecraft.