A closed-loop system (10; 54) comprising: a pump configured to drive a fluid through a series of conduits, the pump including a pump inlet configured to receive fluid from within the series of conduits and a pump outlet; a boot strap reservoir (20; 56) in fluid communication with the series of conduits, the boot strap reservoir (20; 56) including a high pressure chamber in communication with the pump outlet and a low pressure chamber (26; 58) in communication with the pump inlet, wherein the high pressure chamber includes an area that is different than an area of the low pressure chamber; a hydraulic device configured to operate responsive to fluid flow through the conduits of the system (10; 54), wherein the device generates pressure variations within the system (10; 54) during operation; and a valve configured to regulate a pressure drop between the pump inlet and the pump outlet and thereby the resulting pressure encountered by the high pressure chamber to minimize a maximum pressure range of the system (10; 54), wherein during operation the hydraulic device additionally exhausts fluid through the series of conduits back to the pump inlet; characterized in that the low pressure chamber (26, 58) is separated by a piston from the high pressure chamber, the piston being movable responsive to a pressure differential between the high pressure chamber and the low pressure chamber (26;58), the closed loop system comprises a pressure sensor (38; 42) for sensing a pressure within the system (10; 54) indicative of pressure at the pump inlet; the valve is disposed within the series of conduits between the pump and the hydraulic device; and the system is configured such that modulation of the valve can vary the pressure drop between the pump outlet and the device. a pump configured to drive a fluid through a series of conduits, the pump including a pump inlet configured to receive fluid from within the series of conduits and a pump outlet; a boot strap reservoir (20; 56) in fluid communication with the series of conduits, the boot strap reservoir (20; 56) including a high pressure chamber in communication with the pump outlet and a low pressure chamber (26; 58) in communication with the pump inlet, wherein the high pressure chamber includes an area that is different than an area of the low pressure chamber; a hydraulic device configured to operate responsive to fluid flow through the conduits of the system (10; 54), wherein the device generates pressure variations within the system (10; 54) during operation; and a valve configured to regulate a pressure drop between the pump inlet and the pump outlet and thereby the resulting pressure encountered by the high pressure chamber to minimize a maximum pressure range of the system (10; 54), wherein during operation the hydraulic device additionally exhausts fluid through the series of conduits back to the pump inlet; characterized in that the low pressure chamber (26, 58) is separated by a piston from the high pressure chamber, the piston being movable responsive to a pressure differential between the high pressure chamber and the low pressure chamber (26;58), the closed loop system comprises a pressure sensor (38; 42) for sensing a pressure within the system (10; 54) indicative of pressure at the pump inlet; the valve is disposed within the series of conduits between the pump and the hydraulic device; and the system is configured such that modulation of the valve can vary the pressure drop between the pump outlet and the device.