A system for maintaining pressure in the liquid fuel tank of a high-speed flight vehicle, such as a hypersonic flight, scramjet powered air and space vehicle, manages tank ullage using a pressure regulator coupled to the fuel tank that supplies pressurized gaseous media into the fuel tank ullage based on the internal pressure of the tank. The regulator has an on-board controller that processes tank pressure input to deliver a pulse-width modulated input signal to the coil of the on-board solenoid metering assembly. Energizing the coil drives the metering valve open against spring force. The metering assembly is contained in a removable cartridge that has a floating valve guide that is held stationary by bias of the spring against the metering valve. The metering valve has a separate valve seat that mates with the metering orifice of a flow nozzle. The valve seat can have higher compressibility than a clapper part of the valve to effect a better seal, with its compression being controlled by contact of the clapper with a rigid stop surface of the flow nozzle.