A manifold block for use in a portable positive pressure ventilator system (100,100') comprising a ventilator for providing respiratory support to a patient, the manifold block comprising: a) three chambers that are formed within its interior, wherein: i) a first chamber comprises a diaphragm of a main inspiratory valve, which is a diaphragm valve, which works by activating the diaphragm to move up and down to cause opening and closing of a fluid passage; ii) a second chamber is configured as an inspiratory valve first connector, which is a chamber into which gas from a source of pressurized air enters the manifold block; and iii) a third chamber is configured as an inspiratory valve second connector, which is a chamber connected at a proximal end of the third chamber to a tubing system that leads to the patient; b) a wall that separates the second chamber from the third chamber; c) a small diameter hole that passes through the wall; d) an outlet for an anti-asphyxia valve and all flow paths (49,204,81) needed for fluidly connecting and operating components (42,43,45,80,84,86) of the ventilator created within walls of the manifold block; e) an opening leading from the first chamber into the second chamber, which is opened and closed by the diaphragm of the main inspiratory valve when the main inspiratory valve is activated by an inspiratory valve controller; and the manifold block characterized in that, the small diameter hole that passes through the wall is configured to be a continuous bleed aperture. a) three chambers that are formed within its interior, wherein: i) a first chamber comprises a diaphragm of a main inspiratory valve, which is a diaphragm valve, which works by activating the diaphragm to move up and down to cause opening and closing of a fluid passage; ii) a second chamber is configured as an inspiratory valve first connector, which is a chamber into which gas from a source of pressurized air enters the manifold block; and iii) a third chamber is configured as an inspiratory valve second connector, which is a chamber connected at a proximal end of the third chamber to a tubing system that leads to the patient; i) a first chamber comprises a diaphragm of a main inspiratory valve, which is a diaphragm valve, which works by activating the diaphragm to move up and down to cause opening and closing of a fluid passage; ii) a second chamber is configured as an inspiratory valve first connector, which is a chamber into which gas from a source of pressurized air enters the manifold block; and iii) a third chamber is configured as an inspiratory valve second connector, which is a chamber connected at a proximal end of the third chamber to a tubing system that leads to the patient; b) a wall that separates the second chamber from the third chamber; c) a small diameter hole that passes through the wall; d) an outlet for an anti-asphyxia valve and all flow paths (49,204,81) needed for fluidly connecting and operating components (42,43,45,80,84,86) of the ventilator created within walls of the manifold block; e) an opening leading from the first chamber into the second chamber, which is opened and closed by the diaphragm of the main inspiratory valve when the main inspiratory valve is activated by an inspiratory valve controller; and