A respiratory treatment apparatus configured to provide a flow of breathable gas to a patient, including a breathable air outlet (16), an outside air inlet (34), and a pneumatic block module (56), wherein the pneumatic block module includes: a volute assembly (108) including an inlet air passage, a mount for a blower and an outlet air passage； the blower being mounted in the mount such that an impeller of the blower is in a flow passage connecting the inlet air passage and the outlet air passage； a casing enclosing the volute assembly, wherein air passages within the casing connect air ports on the volute assembly, wherein the inlet air passage of the volute assembly is in fluid communication with the outside air inlet and the outlet air passage of the volute assembly is in fluid communication with the air outlet.
