the pneumatic spring 10 shown in fig1 and 2 comprises an air bellows 14 with an upper , body - side region 16 , whose upper end is closed by means of an end portion 30 . via a compressed air opening 12 provided in the upper portion 30 compressed air is supplied to the interior space 11 of the air bellows 14 via a compressed air line 13 and an only schematically shown source of compressed air p . in order to ventilate the interior space there is provided a valve 20 — in this first embodiment decentrally , i . e . not on the axis of symmetry — which valve is designed as a one - way valve 210 . the valve 210 comprises a nozzle 212 which projects into the interior space 11 and is formed of an elastic tube 214 and which has an opening 211 . the elastic tube 214 is supported on its first , body - side end 215 in a valve seat 213 . at its second , axle - side end 216 the elastic tube 214 is designed such that it tightens or contracts due to its internal stress to such an extent that there is no axial air passage . this state is shown in fig2 . in case there is a pressure in the interior space 11 which is greater than the pressure in the exterior , the valve 210 is additionally brought or pressurized into its closed position . at the top of the end portion 30 there is a dome - shaped hollow cover 218 which is provided with air openings 219 at its bottom , through which the air may flow into the interior of the cover 218 . the elastic tube 214 is designed such that , as soon as the pressure in the interior space 11 falls bellow a certain degree and , thus , there is a positive pressure at the exterior , it widens at its second end 216 and provides or sets free an opening 211 through which the air from the surroundings or from the exterior may flow into the interior space 11 . this situation occurs when for example a vehicle provided with such an air bellows is lifted by a crane and the air bellows unrolls or unfolds so that its volume enlarges and its interior pressure decreases accordingly . such replenishment of air , which is indicated by arrows b in fig1 , from the exterior into the interior space 11 thus may reliably prevent that a negative pressure develops in the air bellows 14 , which would hinder a correct rolling or folding and unrolling or unfolding of the air bellows 14 . according to the invention such a compensation of pressure may be ensured by the valve 20 or 210 independent from the source of compressed air p and thus independent from the respective operational situation of a vehicle provided with the pneumatic spring . as soon as sufficient pressure has built up in the interior space 11 , the elastic tube 214 contracts again at its elastic end 216 , thus closing the opening 211 . the pressure acting on the valve 210 is indicated by arrows a in fig2 . due to the design of the valve 210 as a one - way valve , air may not be pressed out of the interior space 11 . it should be noted that the term “ nozzle ” does not necessarily mean an air passage section having a reduced cross - section — as it is shown in fig1 and 2 — but a air passage section of the most general type . the description of the first embodiment and the use of the reference signs applies analogously to the second to sixth embodiments of fig3 to 12 , unless stated otherwise or not feasible technically . in order to avoid unnecessary repetition in the following mainly such details are described hereinafter in which the further embodiments differ from the first embodiment . fig3 and 4 show a second embodiment of the air bellows 14 according to the invention , wherein a valve 220 is arranged in the body - side end portion 54 of the plunger 50 , which valve is similar to that of the first embodiment . the axle - side region 18 of the air bellows 14 is connected fixedly and airtight to compressed air to the region 56 , which may be designed as an elastomer buffer element , and the end portion 54 of the plunger . similar as in the first embodiment , an elastic tube 224 is arranged in a valve seat 223 such that the elastic tube 224 may provide a connection to the interior space 11 of the air bellows 14 . here , the first , body - side end 225 faces towards the interior space 11 , and the second , axle - side end 226 of the elastic tube 224 faces towards the exterior . in the second embodiment , the first end may contract or tighten to such a degree that no air may pass through the elastic tube 224 into the interior space 11 . according to the second embodiment the first end 225 projects into a chamber 52 which is provided in the end portion 54 . the chamber 52 is in communication with the interior space 11 of the air bellows 14 via an air channel 51 . a cover 228 projects from the valve seat 223 into the interior space of the plunger 50 , wherein the cover 228 at its bottom end is designed to be parallel to the end portion 54 and comprises air openings 229 through which air may pass in the open position of the valve 220 . this state is shown in fig4 , wherein the air flow is indicated by arrows b . the air flows through an opening 221 which is formed by a corresponding positive pressure in the interior space of the plunger 50 in the elastic tube 224 . as soon as there has been a pressure compensation , or the positive pressure in the interior space of the plunger 50 is no longer sufficient , the elastic tube 224 contracts again and forms an airtight barrier of the plunger towards the interior space 11 of the air bellows 14 . the pressure acting in this static situation is indicated by arrows a in fig3 . fig5 and 6 show a third embodiment of the air bellows 14 according to the invention , wherein fig5 shows the closed position of the valve 230 contained therein , while fig6 shows the opened position of the valve 230 . different from the second embodiment , the valve 230 is slid onto a tubule 237 by means of an elastic tube 234 since it provides a connection between the interior space of the plunger 15 and the interior space 11 of the air bellows and , to this end , intersperses the end portion 54 of the plunger 50 . the functioning of the valve 230 with its first , body - side end 235 and its second , axle - side end 236 as well as the respective pressure and flow situations with the respective arrows a and b is the same as in the second embodiment . the elastic tube 234 as well as the section of the tubule 237 onto which it is slid or put are located in an air channel 51 which is provided in the body - side region 56 of the plunger — which is preferably designed as an elastomer buffer element . the elastic tube 214 , 224 and 234 , respectively , preferably is made of an elastic rubber or another elastic material having suitable properties . fig7 and 8 show a fourth embodiment of the air bellows 14 according to the invention , which is provided with a valve 240 . the valve 240 , as is the case in the second and third embodiments , is arranged on the axis of symmetry of the air bellows 14 and , here , is designed as an essentially plate - shaped , axially slidable closing piece 242 . the closing piece 242 is arranged in a chamber 52 which is defined or limited by the body - side region 56 — which is preferably designed as an elastomer buffer element — and the end portion 54 of the plunger 50 , and has a central guiding portion 245 which extends in the axial direction and ends in a thickened end portion 242 . the central guiding portion 245 is guided in a guiding bore 247 which axially intersperses the end portion 54 of the plunger 50 , and the thickened end portion 246 is located outside of the chamber 52 . consequently , the closing piece 242 is supported in the chamber 52 in a movable manner and in such a way that it will not get lost . in case there is a positive pressure in the interior space 11 of the air bellows 14 relative to the interior space of the plunger 50 , the closing piece 242 is pushed onto the end portion 54 and closes air openings 249 which intersperse the end portion 54 from the interior space of the plunger 50 to the chamber 52 . as as soon as there is sufficient positive pressure in the interior space of the plunger 50 , the closing piece 242 will be axially displaced away from the end portion 54 towards the body - side end of the chamber 52 and the air may flow through the air openings 249 into the chamber 52 , and from there via an air channel 51 into the interior space 11 of the air bellows 14 , as is indicated by arrows b . the closing piece 242 preferably is made from an elastic rubber or another elastic material having suitable properties . fig9 and 10 show a fifth embodiment of the present invention , which is similar to the fourth embodiment . a valve 250 is designed similar to the fourth embodiment with a closing piece 252 , a central guiding portion 245 , a thickened end portion 246 as well as a guiding bore 247 . the main difference to the fourth embodiment is that the valve 250 is arranged entirely in the chamber 52 , which is defined or limited by the body - side region 56 — which preferably is designed as elastomer buffer element — and the end portion 54 of the plunger 50 . in a valve seat 253 there is provided a recess 58 in the body - side region 56 of the plunger 50 , in which the closing piece 252 may move . air openings 261 intersperse the valve seat 253 and , thus , form a connection between the recess 58 and the chamber 52 , wherein the chamber 52 communicates with the interior space of the plunger 50 via an air opening 259 which intersperses the end portion 54 . the recess 58 , in turn , communicates with the interior space 11 of the air bellows 14 via an air channel 51 . the movement of the valve 250 from the opened and closed positions and vice versa is very similar to the fourth embodiment . the closing piece 252 preferably is made from an elastic rubber or another elastic material having suitable properties . fig1 and 12 show a sixth embodiment of the invention . similar to the fifth embodiment , there is formed a valve 260 in a recess 58 of a valve seat 263 , wherein the valve seat 263 is formed in a chamber 52 which is defined or limited by a body - side region 56 — which is preferably designed as an elastomer buffer element — and the end portion 54 of the plunger 50 . a membrane 262 is held in a membrane holder 265 which forms part of the valve seat 263 . the recess 58 above the membrane 262 communicates with the interior space 11 of the air bellows 14 via an air channel 51 . below the membrane 262 , there are provided air openings 261 which axially intersperse the valve seat 263 and provide a connection between the space 267 below the membrane 262 and the chamber 52 . the chamber 52 , in turn , is connected to the interior space of the plunger 50 via air openings , which are not explicitly shown in the drawings . in the case of a corresponding negative pressure in the interior space 11 of the air bellows the membrane 262 , as is shown in fig1 , is essentially clamped in the membrane holder 265 in a non - deflected manner . via air channels 269 , which intersperse the membrane holder 265 and provide a connection between the space 267 and the recess 58 , when the membrane 262 is not deflected , air may pass from the interior space of the plunger 50 via the air openings 261 and the space 267 into the recess 58 , and via the air channel 51 further into the interior space 11 of the air bellows 14 . in case the pressure in the interior space 11 of the air bellows 14 increases by a certain degree , the membrane 262 is deflected towards the bottom to such an extent that it closes the air openings 261 . this closed position is shown in fig1 . the fact that the membrane 262 is arranged in the recess 58 or in the chamber 52 , respectively , ensures that the valve 262 is highly protected from disturbing influences such as dirt or mechanical influences . the membrane 262 preferably is made from an elastic rubber material or another suitable material having sufficient elasticity . the air bellows of the invention usually is provided with a relatively soft spring stiffness and , thus , usually is of little importance for springing or suspension purposes . thus , the air bellows only serves to adjust the height of the vehicle above the axle , while damping is done via suitable suspension arms . as a matter of course , individual features of certain embodiments such as the site and the exact design of individual components of the valve may also be realized in other embodiments , insofar as this is not explicitly excluded in the description or prohibits itself for technical reasons .