A rapidly modulated hydraulic supply, comprising: a cylindrical chamber for receiving fluid; a displacement member operable to displace the fluid from the cylindrical chamber the displacement member comprising a piston disposed in the cylindrical chamber and configured for reciprocal movement therein; and a flow modulation system operable to vary the flow rate of the fluid output from the cylindrical chamber, wherein the flow modulation system comprises a first portion and a second portion of the piston moveable relative to one another, wherein the second portion of the piston forms a sleeve about the first portion of the piston; and a coupling mechanism configured to selectively couple and uncouple the first portion and the second portion of the piston to and from one another, wherein the coupling mechanism comprises a pin and an actuator to cause the pin to couple and uncouple the first portion and the second portion of the piston to and from one another; wherein a first flow rate corresponds to a first output pressure, and is different from a second flow rate corresponding to a second output pressure for a similar movement of the displacement member within the cylindrical chamber; wherein, when the first portion and the second portion of the piston are coupled to one another, reciprocal movement of the first portion and the second portion of the piston within the cylindrical chamber provides the first flow rate; and wherein, when the first portion and the second portion of the piston are uncoupled from one another, reciprocal movement of the first portion of the piston within the cylindrical chamber provides the second flow rate lower than the first flow rate characterized in that the actuator comprises a solenoid, an electric motor, a pneumatic actuator, a hydraulic actuator, or a combination thereof. a cylindrical chamber for receiving fluid; a displacement member operable to displace the fluid from the cylindrical chamber the displacement member comprising a piston disposed in the cylindrical chamber and configured for reciprocal movement therein; and a flow modulation system operable to vary the flow rate of the fluid output from the cylindrical chamber, wherein the flow modulation system comprises a first portion and a second portion of the piston moveable relative to one another, wherein the second portion of the piston forms a sleeve about the first portion of the piston; and a coupling mechanism configured to selectively couple and uncouple the first portion and the second portion of the piston to and from one another, wherein the coupling mechanism comprises a pin and an actuator to cause the pin to couple and uncouple the first portion and the second portion of the piston to and from one another; a first portion and a second portion of the piston moveable relative to one another, wherein the second portion of the piston forms a sleeve about the first portion of the piston; and a coupling mechanism configured to selectively couple and uncouple the first portion and the second portion of the piston to and from one another, wherein the coupling mechanism comprises a pin and an actuator to cause the pin to couple and uncouple the first portion and the second portion of the piston to and from one another; wherein a first flow rate corresponds to a first output pressure, and is different from a second flow rate corresponding to a second output pressure for a similar movement of the displacement member within the cylindrical chamber; wherein, when the first portion and the second portion of the piston are coupled to one another, reciprocal movement of the first portion and the second portion of the piston within the cylindrical chamber provides the first flow rate; and wherein, when the first portion and the second portion of the piston are uncoupled from one another, reciprocal movement of the first portion of the piston within the cylindrical chamber provides the second flow rate lower than the first flow rate characterized in that the actuator comprises a solenoid, an electric motor, a pneumatic actuator, a hydraulic actuator, or a combination thereof.