in fig1 an inhalation therapy unit is represented , which includes a cylindrical basic body 1 and a connecting piece 2 formed thereon . in the interior of the cylindrical basic body 1 , i . e . in the nebulisation chamber , an atomizer nozzle ( not shown , see e . g . ep - b - 0 281 650 ) is arranged , which generates an aerosol from a medicine stored in the inhalation therapy unit . for this purpose , compressed air is supplied to the atomizer nozzle via a pressure medium supply line 3 . a mouthpiece is generally arranged on the connecting piece 2 via which the patient can inspire the aerosol generated in the nebulisation chamber . from the upper end of the cylindrical basic body 1 in fig1 a cylindrical air intake flue ( not shown , see for example ep - b - 0 281 650 ) projects into the nebulisation chamber . through this air intake flue , ambient air can further flow into the interior of the inhalation therapy unit when the patient inspires the aerosol via the mouthpiece mounted on the connecting piece 2 . the outwardly facing opening of the air intake flue is closed by a passive limiting valve 4 , which is constructed as one - way valve and the assembly of which is described in more detail in the following with reference to fig2 . fig2 a shows the passive limiting valve 4 from the outwardly facing side , i . e . from the side to be seen also in fig1 . fig2 b shows the passive limiting valve 4 on the side facing the air intake flue , which is not visible in fig1 . fig2 c shows a cross - section through the passive limiting valve along the line a — a in fig2 b . in fig2 a to 2 c it can be seen that the passive limiting valve 4 of the embodiment of the invention here described includes a cylindrical basic body 10 having a surface formed in a plurality of stages and a closure wall 11 perpendicular to the cylinder axis . in the closure wall 11 , a plurality of air inlet openings 12 are provided , which can also be defined as through openings and through which ambient air can flow into the interior of the inhalation therapy unit . in the cylinder section 10 a with the smallest outer diameter , a valve member 13 is provided which has the shape of a circular valve platelet with a centric securement opening . the valve platelet 13 is made of an elastic material , for example silicone , with a sufficient stiffness of its own which guarantees that the valve platelet 13 , in the non - deflected idle position , closes the air inlet openings 12 of the limiting valve 4 . as can be recognized in fig2 c , a circular sealing lip 14 can be provided as support on the side of the closure wall 11 facing the valve platelet . for securement , the valve platelet 13 is placed on a pin 15 extending along the cylinder axis on the side of the limiting valve 4 facing the interior of the inhalation therapy unit . by this assembly , the following function is realized . when the patient breathes through the inhalation therapy unit , the valve platelet is deflected and permits the flowing in of intake air through the air inlet openings 12 of the limiting valve . the resultant opening cross - section is extensively proportional to the underpressure which has built up in the nebuliser chamber . in the breathing intervals , or when the patient expires into the inhalation therapy unit , the valve member 13 closes the openings 12 . according to the invention , on the side of the valve platelet 13 lying opposite the closure wall 11 , a limiting member 16 is arranged which limits the deflection of the valve platelet 13 . the limiting element 16 has the shape of a circular disc with a centrically arranged securement opening . the outer diameter of the limiting member 16 substantially corresponds with the inside diameter of the cylinder section loa . the limiting member 16 is also placed on the pin 15 extending along the cylinder axis , so that the valve platelet 13 and the limiting member 16 are aligned with each other . the limiting member 16 has air passage orifices 17 , which are sufficiently large so as not to offer any great resistance to the flowing through of the suctioned air when the valve platelet 13 is only deflected so far that it does not abut against the limiting member 16 . the ambient air then flows through the air inlet openings 12 and around the valve platelet 13 in order subsequently to enter into the interior of the inhalation therapy unit via the air passage orifices 17 . via the self restoring force of the valve platelet 13 , a flow path is created having an opening cross - section which is proportional to the underpressure in the interior of the inhalation therapy unit , i . e the pressure difference across the valve , as long as the patient breathes within the aerosol - physically desirable pressure / flow range . if the underpressure exceeds a certain limit , the valve platelet 13 abuts against the facing surface of the limiting member 16 , whereby the air passage orifices 17 of the limiting member are almost completely closed . on account of the shape of the air passage orifices 17 , however , the orifices remaining open for the passage of air have a strongly reduced cross - section . the remaining orifices are defined in the following as air passage auxiliary orifices ; they can be provided separately from the air passage orifices 17 , or realized as part of these orifices . the cross - section of these orifices does not change any more if the underpressure is further increased , i . e . if the patient tries to inspire more strongly . this leads to an exponentially increasing flow - through resistance upon a further increase of the underpressure , as can be taken from the diagram in fig3 ( see curves x , y and z ). this finally leads to a reduction of the inspiration flow in the desired target value range . this target value range is dependent on the deflection of the valve platelet and on the cross - section of the auxiliary openings and can therefore be adjusted in broad limits . the air passage orifices 17 of the limiting member 16 are advantageously constructed so that they have as large an area as possible and are aligned with the valve platelet 13 . the contour 17 a of the air passage orifices 17 extending along the outer edge of the valve platelet is designed in the shown embodiment in such a manner that even upon abutment of the valve platelet 13 a part of the air passage orifices 17 remain open as auxiliary orifices 17 b through which air can further flow . these auxiliary orifices are very much smaller than the air passage orifices . the previously mentioned contour of the air passage orifices 17 is for example of undulatory or zig - zag shape . fig2 b reveals an undulatory shape of the contour 17 a of the air passage orifices 17 in the region corresponding to the outer edge of the valve platelet . if the valve platelet 13 abuts against the limiting member 16 , only the radially outwardly projecting sections of the air passage orifices 17 remain open as auxiliary orifices 17 b whereas the far greater portion of the air passage orifices is closed by the valve platelet 13 . accordingly , the corresponding contour 17 a of the air passage orifice 17 of the limiting member 16 interacts with the outer edge of the valve platelet 13 , so that also when the valve platelet 13 abuts , orifices remain through which the air can flow . these orifices are preferably parts of the air passage orifices 17 which , when the valve platelet does not abut against the limiting element as a whole are available for the flow - through of the air . however , when the valve platelet abuts , these sections represent auxiliary orifices through which air can further flow , but on account of the reduced cross - section , with an increased flow resistance . the interaction of the outer edge of the valve platelet with the corresponding contour of the air passage orifice represents a special characteristic of the invention . with this construction , a valve is created which provides , with increasing pressure difference , firstly proportional air passage orifices with maximum cross - section , and upon reaching a threshold value of the pressure difference , only air passage auxiliary orifices with clearly reduced and constant cross - sectional area for the air flow .
a limiting valve is provided in an inhalation therapy unit with a valve member which closes an air through opening in the idle state and corresponding to the pressure difference occurring over the valve opens same substantially proportionally up to a threshold value . if the threshold value is exceeded , the valve member abuts against a limiting member which limits the movement of the valve member and the air passage orifices of which are partially closed by the valve member so that air can only flow through the air passage auxiliary orifices remaining free . in this manner the patient using the inhalation therapy unit is urged to breath in the range below the threshold value , as his respiration above the threshold value is opposed by a considerably higher resistance .