A bias valve for a mechanical ventilator having an exhalation control module and a Roots blower producing a pulsating gas flow, and configured for being fluidly connected to a patient circuit and exhalation valve, the bias valve comprising: a housing assembly having an annular housing chamber opening to a housing outlet and a housing inlet, the housing assembly including: a housing having a housing sidewall and a housing end wall, the housing inlet being formed on an end of the housing opposite the housing end wall, the housing outlet being formed on the housing sidewall; a hollow cylinder fixedly mounted within the housing and having a cylinder end wall and a cylinder sidewall, the cylinder sidewall being disposed in spaced coaxial relation to the housing sidewall to define the housing chamber therebetween, the cylinder being open on an end coincident with the housing inlet; and an annular valve seat fixedly mounted to the housing inlet and having a seat interface, the annular valve seat configured to fluidly connect to the Roots blower; a poppet slidably disposed within the cylinder, the poppet having a poppet side and opposing poppet ends, a cylinder chamber being defined between the cylinder end wall and one of the poppet ends, the other one of the poppet ends being configured to be sealingly engageable to the seat interface and defining a seat area, the poppet being reciprocatively moveable between closed and open positions for respectively preventing and allowing gas to flow from the Roots blower to the patient circuit; and a biasing member (76, 78) having a spring preload configured to bias the poppet against the seat interface, the seat area and spring preload sized configured to provide a predetermined bias pressure at the exhalation control module for regulation of an exhalation valve connected to the patient circuit. a housing assembly having an annular housing chamber opening to a housing outlet and a housing inlet, the housing assembly including: a housing having a housing sidewall and a housing end wall, the housing inlet being formed on an end of the housing opposite the housing end wall, the housing outlet being formed on the housing sidewall; a hollow cylinder fixedly mounted within the housing and having a cylinder end wall and a cylinder sidewall, the cylinder sidewall being disposed in spaced coaxial relation to the housing sidewall to define the housing chamber therebetween, the cylinder being open on an end coincident with the housing inlet; and an annular valve seat fixedly mounted to the housing inlet and having a seat interface, the annular valve seat configured to fluidly connect to the Roots blower; a housing having a housing sidewall and a housing end wall, the housing inlet being formed on an end of the housing opposite the housing end wall, the housing outlet being formed on the housing sidewall; a hollow cylinder fixedly mounted within the housing and having a cylinder end wall and a cylinder sidewall, the cylinder sidewall being disposed in spaced coaxial relation to the housing sidewall to define the housing chamber therebetween, the cylinder being open on an end coincident with the housing inlet; and an annular valve seat fixedly mounted to the housing inlet and having a seat interface, the annular valve seat configured to fluidly connect to the Roots blower; a poppet slidably disposed within the cylinder, the poppet having a poppet side and opposing poppet ends, a cylinder chamber being defined between the cylinder end wall and one of the poppet ends, the other one of the poppet ends being configured to be sealingly engageable to the seat interface and defining a seat area, the poppet being reciprocatively moveable between closed and open positions for respectively preventing and allowing gas to flow from the Roots blower to the patient circuit; and a biasing member (76, 78) having a spring preload configured to bias the poppet against the seat interface, the seat area and spring preload sized configured to provide a predetermined bias pressure at the exhalation control module for regulation of an exhalation valve connected to the patient circuit.