A pressure regulator includes a housing, a metering spool, a first pressure chamber at a reference pressure to which one end of the metering spool is exposed, a spring within the first pressure chamber acting against the one end of the metering spool, a second pressure chamber containing hydraulic fluid at the regulated pressure acting against the opposite end of the metering spool, wherein the position of the metering spool relative to the housing is a position of equilibrium that changes to maintain a predetermined pressure difference between the reference pressure and the regulated pressure. An abutment against which the opposite end of the spring reacts is provided and a third pressure chamber at a control pressure acts on the abutment, such that the control pressure can be changed to adjust the position of the abutment to change the pre-load of the spring to adjust the value the predetermined pressure difference.