Abstract: A pressure control system is disclosed for closely regulating the pressure level of a controlled volume. The system comprises first and second sources, a throttled valve for controlling the flow rate of the fluid between each of the first and second pressure sources and the controlled volume, and a feedback control. The throttled valve comprises a rotationally mounted cam, a housing for receiving the cam and including a chamber, a first port coupled to the first pressure source, a second port coupled to the controlled volume, and a third port coupled to the second pressure source. The cam has first and second cam surface portions for defining corresponding first and second transfer functions of fluid flow through the first and second ports, respectively. First and second metering needles are associated with the first and third ports respectively for throttling the fluid flows therethrough. The first and second metering needles are disposed to engage respectively the first and second cam surface portions.