with reference to the drawing , and particularly to the fig1 thereof , the illustrated device comprises , as known per se , a body member i formed with an interior cylindrical chamber 2 communicating at an end thereof with an air inlet conduit s connected to the first stage of the regulator , and including at the other end thereof an opening 4 which constitutes a valve seat on the outer side thereof . concentric with the chamber 2 is a cylindrical conduit slidably accommodating a small piston 7 . said piston 7 is formed with an axial exactly - dimensioned hole 117 and comprises , on the end facing towards the valve seat 4 of said chamber 2 , an annular seal 5 which normally rests against said valve seat to close it . said piston 7 is constantly urged against the valve seat 4 by a spring b abutting at an end thereof against said piston 7 and at the other end thereof against an apertured partition 9 arranged across the conduit 0 . said partition 9 is provided with a central hole 10 which is formed as a valve seat on its side far from said piston 7 . the valve seat on the hole 10 co - operates with a valve member 11 mounted on a pivotable lever 12 which co - operates with a manostat diaphragm 13 mounted on the body member 1 of the regulator . said conduit b , upstream of the piston 7 , is formed with a hole 14 for communicating with a conduit 15 which is connected to the mouthpiece for the user . said lever 12 is pivotably mounted on a fulcrum 10 and is constantly urged by a spring 17 housed within the body member 1 , so as to seat the valve member 11 against the valve seat 10 . in the position shown in fig1 i . e . with the valve member 11 matched against the valve seat 10 , and with the valve member 5 matched against the valve seat 4 , the regulator prevents any flow of air from the conduit s to the conduit 15 . as soon as a user effects a breathing act ( normal breathing condition ), the reduced pressure created within the body member i causes , through the displacement of the diaphragm is , the lever 12 to pivot against the action of the spring 17 , whereby the valve member 11 is moved away from its valve seat permitting the air to flow from the conduit s to the chamber 2 and successively through the hole 4 , the hole 117 of the piston 7 , the valve seat 10 and the hole 18 in the wall of the conduit 6 , downstream of the piston 7 , to the conduit 15 . whenever a larger amount of oxygen is required , for example , due to a panting condition , a still more reduced pressure is created and causes the piston 7 to be lifted from the seat 4 against the action of the spring b . in this instance , the air from the chamber 2 flows directly into the conduit 15 through the openings 4 and 14 . a double flow of air to the conduit 15 is thus established to meet the user &# 39 ; s increased demand of oxygen . as soon as this increased demand ceases , the valve member 5 of said piston 7 is urged back against its seat 4 to close it , whereby the supply of air will be regulated again by the valve member under the control of the diaphragm 13 . in the embodiment shown in the fig2 and 4 , the piston 7 is replaced by a valve member 7 &# 39 ; comprising a metallic tubular element 107 &# 39 ; enwrapped circumferentially by a rubber shell 207 &# 39 ; extending radially inwards at one end thereof so as to form a diaphragm 307 &# 39 ; having a central hole wherein a metal nozzle 407 &# 39 ; with a central exactly - dimensioned through - hole 117 is sealingly embedded . according to this embodiment , the valve member 7 &# 39 ; is not slidable in the tubular conduit 6 as its upper end abuts against the partition 9 and its opposite end rests against the valve seat 4 through said diaphragm 307 &# 39 ;. the operation of the just - described device is apparent . in the condition of increased air demand , the diaphragm 307 &# 39 ; is lifted from said seat 4 by virtue of its resiliency , thus permitting the air to pass from the seat 4 through the by - pass hole 14 to the conduit 15 . fig3 shows a modification of the valve member 7 &# 39 ; of the fig2 and 4 . according to this modification , the valve member comprises a cylindrical metallic body 507 &# 39 ; provided with a sealing o - ring 007 &# 39 ; on its outer surface . the bottom end of the body 507 &# 39 ; is closed by a rubber diaphragm 707 &# 39 ; having a central hole wherein a nozzle 407 &# 39 ; with an exactly - dimensioned through - hole 117 is embedded . the arrangement and operation of this valve member are exactly the same as those described above in connection with the embodiment of the fig2 and 4 . during the normal use , the lever 12 is subjected to a minimum pressure and opens the valve member 11 , thus permitting the flow of air through the exactly - dimensioned hole 117 and the opening 10 to the conduit 15 so as to permit a good breathing . if , due to any reason , the demand of air increases , the servo - control mechanism is activated whereby the larger valve 4 is opened and an additional flow of air is delivered to the conduit 15 , through said by - pass circuit , so as to eliminate any damping condition immediately .