There is no special definition of the cylinder. The so-called pressure classification is the pump.
Low voltage (L) container 0.1 MPa < p < 1.6 MPa;
MV (M) container 1.6 MPa < p < 10 MPa;
High pressure vessel (H) 10 MPa < p < 100 MPa;
Ultra high pressure (U) or 100MPa P container. (1MPa=9.8Kg)
As for the pressure of the cylinder, it is designed according to the rated pressure of the system. The pressure of the system pressure high cylinder will be high.