Compressed-air system having a safety function and method for operating such a compressed-air system

Abstract

A compressed-air system having a safety function and a method for operating such a compressed-air system. The compressed-air system contains two working valves, which each can selectively assume an aerating position that aerates a load and a venting position that vents the load. Both working valves are redundantly connected on the output side to the load by means of a separating device. The separating device allows one or the other of the working valves to be separated, while the aeration of the load is maintained, in order to subject the one or the other working valve to an examination of the switching function of the one or the other working valve.

Claims

1. A compressed-air system having a safety function, with a first and a second working valve, each of which has a working connection and a venting connection connected or connectable to the atmosphere, wherein the two working connections are connected in parallel fluid communication with one and the same load connection of the compressed-air system which load connection is connected or connectable to a load, wherein each working valve is switchable into a venting position, connecting its working connection with its venting connection and wherein the two working valves can simultaneously assume their venting position, and wherein each working valve also has a supply connection connected or connectable to a compressed-air source and selectively is switchable to an aerating position connecting its working connection with its supply connection or to its venting position, and wherein the venting cross-section enabled in the venting position by each working valve for flow of compressed air is bigger than the maximum aerating cross-section that can be enabled in the aerating position, and wherein, in the connection between the two working connections and the load connection, a separating device is inserted, allowing a temporary fluid-tight separation selectively of the working connection of the first working valve or of the working connection of the second working valve of both the load connection and the working connection of the respective other working valve and in doing so maintains a fluid communication between the load connection and the working connection not separated, and wherein switching function examination means are assigned to the two working valves which are able to check the switching function at least of the working valve, the working output of which is currently separated by the separating device from the load connection and from the working output of the other working valve, while this other working valve assumes its aerating position.

2. A compressed-air system according to claim 1, wherein the separating device is designed as fluid pressure-controlled OR valve connected with both the two working connections and with the load connection, which is able to be switched over as a result of the pressure differential present at the two working connections.

3. A compressed-air system according to claim 1, wherein the separating device is designed as a multi-position valve which can be operated independently of the fluid pressures present on the working connections and which in a neutral position enables fluid communication between the two working connections and the load connection and which furthermore can be switched over alternately to one of two respective separated positions, in each of which it separates one of the two working connections in a fluid-tight manner from the load connection and from the respective other working connection and at the same time enables a fluid communication between the load connection and the respective other working connection.

4. A compressed-air system according to claim 1, wherein the switching function examination means contain position detection means responding to a positional change of a valve member of the working valve .

5. A compressed-air system according to claim 1, wherein the switching function examination means have pressure detection means, responding to a pressure change in the fluid pressure at the working connection upon switchover of the working valve.

6. A compressed-air system according to claim 1, wherein to each working valve is assigned a control air reservoir, which in the venting position can be vented via the related working valve, wherein detection means are present, through which a time-dependent pressure change or a flow of the associated compressed air venting flow can be detected and wherein either an own control air reservoir is assigned to each working valve or a common control air reservoir is assigned to both working valves.

7. A compressed-air system according to claim 6, wherein the control air reservoir is connected either to a working connection or to a filling connection of at least one of the working valves, wherein the filling connection is separate to the working connection and is connectable to the supply connection alternatively to the working connection.

8. A compressed-air system according to claim 1, wherein the separating device has self-function examination means assigned to it, through which the separating function of the separating device can be examined, while both working valves assume the aerating position.

9. A compressed-air system according to claim 8, wherein the self-function examination means of the separating device have position detection means responding to the positional change of a control valve member of the separating device.

10. A compressed-air system according to claim 1, further comprising an electronic controller, through which with uninterrupted aeration of the load connection a test procedure examining the function of the working valves can be brought about, in which starting from an operational state in which both working valves assume the aerating position, first one and then the other working valve is separated by the separating device from the load connection and from the respective other working valve, wherein the respective separated working valve is operated and by means of the switching function examination means undergoes a switching function examination, while the other working valve which still maintains the venting position, is connected to the load connection.

11. A compressed-air system according to claim 1, wherein the two working valves are electro-pneumatically operable.

12. A method for operating a compressed-air system having a safety function according to claim 1, wherein with uninterrupted aeration of the load connection, an examination process of the functioning of the working valves is carried out, in which based on an operating state, in which both working valves assume the aerating position, initially the first working valve and then the second working valve is separated by the separating device from the load connection and from the respective other working valve, wherein the respective separated working valve, while the other working valve remains connected with the load connection with maintenance of the aerating position, in the course of a test operation activity is switched over to the venting position and a correct switchover is verified with the help of the switching function examination means.

13. A method according to claim 12, wherein the working valve switched over to the venting position during the test operation activity is switched back to the aerating position, once verification of correct switchover to the venting position has taken place.

14. A method according to claim 12, wherein, in a compressed-air system, the separating device of which is designed as a fluid-pressure controlled OR valve, the separation of the first or second working valve from the load connection is brought about in that the working valve to be separated is switched over to the venting position, wherein this switchover to the venting position is at the same time used as a test operation activity.

15. A method according to claim 12, wherein, in a compressed-air system, the separating device of which is designed as a multi-position valve, the separation of the first or second working valve from the load connection is brought about in that the multi-position valve starting from the neutral position is switched over to the one or to the other separated position, whereupon the test operation activity relating to the separated working valve is carried out with assigned switching function examination.

16. A method according to claim 15, wherein, before performing a test operation activity the multi-position valve is tested for correct functional capability, and wherein starting from the neutral position, it is switched over initially to the one and then to the other shut-off position and the correct switchover is verified with the help of the self-function examination means.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained with reference to the attached drawing. This shows as follows:

(2) FIG. 1 the circuit of a preferred design of a compressed-air system according to the invention, and

(3) FIG. 2 the circuit of a further embodiment of the compressed-air system according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) The circuits shown in the drawing implement in each case a safety-related compressed-air system 1 with what is known as a two-channel design. The compressed-air systems 1 are advantageously designed so that in any operating situation they can switch off on a two-channel basis in order to guarantee the reliable venting of a connected load V. Even during a test procedure to test the functional capability of the valve technology, at no time can the compressed-air system lapse into single-channel mode.

(5) The following description relates jointly to all illustrated compressed-air systems 1, unless stated to the contrary in an individual case.

(6) The compressed-air system 1 in the exemplary embodiments is built as what is known as an on-off valve, with the help of which the compressed air supply to a load V can be optionally switched on or off. In the switched-on state the compressed-air system 1 ensures aeration of the load V, thus a supply of compressed air, which the load V needs for its operation. In the switched-off state of the compressed-air system 1 the load V is reliably vented, so that it cannot perform any undesired activities.

(7) The load V can be any number of devices or machines operated with compressed air, wherein one or more systems operated with compressed air may also be involved. A conceivable example would be a production and/or assembly device in the area of automation.

(8) The compressed-air system 1 contains two working valves 2, 3, which in the following are referred to also as first working valve 2 and second working valve 3. The working valves 2, 3 for example be 3/2-way valves, wherein alternatively, however, valves with other functionality can be used.

(9) The working valves 2, 3 are electrically operable. These may be directly electrically operable valves or electro-pneumatically piloted valves. In an electro-pneumatically piloted design, each working valve 2, 3 is assigned at least one electrically operable pilot valve, which can be implemented in the unit with the working valve 2, 3 or also integrated as an individual pilot valve in the compressed-air system 1.

(10) The working valves 2, 3 are preferably monostable valves, which when in the electrically not actuated state assume a basic position defined by a spring means 4. This ensures that in the event of a power failure the working valves 2, 3 switch back to the defined basic position.

(11) Each of the two working valves 2, 3 has at least one supply connection 5, one venting connection 6 and one working connection 7. Each working valve 2, 3 can optionally assume a venting position or an aerating position as shown in the drawing. In order to switch between the two positions at least one valve member 8 of the relevant working valve 2, 3 can be moved and repositioned. The valve member 8 is for example a valve gate.

(12) The venting connection 6 is preferably constantly connected with the atmosphere. The drawing illustrates a silencer 12 connected to the venting connection 6, through which the exhaust air can escape into the atmosphere in muted fashion. Depending on the design of the compressed-air system 1 between the venting connection 6 and the atmosphere further fluid engineering means can be connected, though in the exemplary embodiment this is not the case.

(13) The supply connection 5 is connected with a compressed air source P. The supply connections 5 of both working valves 2, 3 are connected to a common compressed air source P. The compressed-air system 1 can have a system housing, on which pneumatic interface means are present, to which the compressed air source P for connection with the two supply connections 5 can be mechanically connected in a fluid-tight manner.

(14) A double-dot-dash symbol 13 is intended to illustrate that the compressed-air system 1 can have valves and/or fluid engineering means that are not shown that are inserted in the connection between the supply connections 5 and the compressed air source P. These means can serve, in particular, to implement a soft-start function. In the specific exemplary embodiment this is not the case, as here the supply connections 5 have a direct through-connection to the preferably external compressed air source P.

(15) The working connection 7 of each working valve 2, 3 is connected to a load output 14 to which, when the compressed-air system 1 is in operation, the aforementioned load V is connected. Here there is a parallel fluid communication between the between the load V and on the one hand the working connection 7 of the first working valve 2 and the working connection 7 of the second working valve 3. In other words, the load V is connected in parallel with both working connections 7, wherein however in the connection between these three connections a fluid engineering separating device 15 is inserted, able to optional close or enable in a fluid-tight manner a fluid communication between the load V and the two working connections 7 in a manner to be described.

(16) In the venting position of a working valves 2, 3 shown in the drawing there is an open fluid communication between the working connection 7 and the venting connection 6, while at the same time the supply connection 5 is closed. In this venting position, therefore, the load V, where the separating device 15 so allows, is via the working valve 2, 3 in the venting position into the atmosphere.

(17) The separating device 15 has an input connection 16 in fluid communication with the working connection 7 of the first working valve 2 and furthermore a second input connection 17 in fluid communication with the working connection 7 of the second working valve 3. It furthermore has an output connection 18, which preferably simultaneously forms the load connection 14. A first communication channel 22 runs between the first input connection 16 and the working connection 7 of the first working valve 2, while a second communication channel 23 creates a fluid communication between the second input connection 17 and the working connection 7 of the second working valve 3.

(18) In the venting position of the first working valve 2 the first communication channel 22, together with the subsequent channel section connecting to the atmosphere, forms a first venting channel 24. In a corresponding manner the second communication channel 23 in the venting position of the second working valve together with the channel section connecting to it and similarly leading to the atmosphere, forms a second venting channel 25. If a working valve 2, 3 assumes its venting position, the load V can then be vented via the now open venting channel 24, 25 into the atmosphere, wherein the resulting compressed air flow can be referred to as a compressed air venting flow.

(19) If a working valve 2, 3 is switched over to the aerating position, it provides fluid communication between the assigned supply connection 5 and the assigned working connection 7, while the similarly assigned aeration connection 6 is separated. In this way compressed air, as part of a compressed air aerating flow, is able to flow from the compressed air source P through the appropriate working valve 2, 3 to the assigned input connection 16, 17 of the separating device 15 and finally to supply the load V to the load connection 14.

(20) The two working valves 2, 3 are preferably designed so that the venting position forms the basic position.

(21) The two working valves 2, 3 can be switched over independently of one another and can be positioned into either the venting position or the aerating position. The electrical control necessary for this is provided by an electronic controller 26, for practical purposes belonging to the compressed-air system 1. The drawing shows, as dot-dash lines, first and second control lines 27a, 28a leading from the electronic controller 26 to the drive devices 27 and 28 that can be activated electrically of the two working valves 2, 3.

(22) By appropriate control of the two working valves 2, 3 inter alia operating states of the compressed-air system 1 can be set, in which both working valves 2, 3 assume the aerating position or in which the two working valves 2, 3 assume the venting position.

(23) Both the compressed air aerating flow and the compressed air venting flow, occurring between the load V and the working valves 2, 3, pass through the fluid engineering separating device 15. The fluid engineering separating device 15 is in particular a valve, which can take different forms as explained further in the following.

(24) The separating device 15 of the compressed-air system 1 illustrated in in FIG. 1 is designed as an OR valve 15a. It contains a control valve member 32, that can be switched over according to the double arrow 33 between two separated positions, wherein the separated position assumed in each case is dependent upon the current pressure differential present at the two input connections 16, 17 and accordingly that at the working connections 7 of the two working valves 2, 3. If the fluid pressure present at the first input connection 16 is greater than the fluid pressure at the second input connection 17, the OR valve 15a switches over to the first separated position shown, in which a fluid communication between the first input connection 16 and the output connection 14 is enabled and in which at the same time these two connections 16, 14 are separated in a fluid-tight manner from the second input connection 17. Consequently, in the first separated position the load connection 14 including the load V connected thereto is in fluid communication with the working connection 7 of the first working valves 2 and at the same time separated from the working connection 7 of the second working valve 3.

(25) The OR valve 15a switches over itself, without any additional special control, into the second separated position, if the fluid pressure present at the output or at the working connection 7 of the second working valves 3 is greater than that at the output of the first working valve 2. In this case an open fluid communication exists between the load connection 14 and the working connection 7 of the second working valve 3, while at the same time the working connection 7 of the first working valve 2 is separated both from the load V and from the second working valve 3 in a fluid-tight manner.

(26) Therefore, the switching position of the OR valve 15a can be specified via the pressure differential between the two working connections 7, which in turn can be specified with the help of the switching position of the two working valves 2, 3.

(27) In order to apply a high pressure at one of the input connections 16, 17, the assigned working valve 2 or 3 is switched to the aerating position. In order to apply a low pressure, the assigned working valve 2, 3 is simply switched over to the venting position.

(28) If both working valves 2, 3 are simultaneously in the aerating position, the load V, depending on how the control valve member 32 is oriented, is supplied via the first working valve 2 and/or via the second working valve 3 with compressed air. The same applies to the venting in the event that both working valves 2, 3 are switched to the venting position.

(29) In the compressed-air system 1 shown in FIG. 2 the separating device 15 is designed as a multi-position valve 15b, wherein in particular a three-position valve is involved. The multi-position valve 15b can assume a neutral position illustrated in FIG. 2, in which it works similarly to a T-piece and connects both input connections 16, 17 in parallel with free passage with the output connection 18. In normal operation of the compressed-air system of FIG. 2 the multi-position valve 15b remains positioned in this neutral position. If both working valves 2, 3 assume the aerating position, the load V experiences simultaneous aeration by both working valves 2, 3 throughout. Similarly, the load V is in this case simultaneously vented via both working valves 2, 3, if both working valves 2, 3 are switched over to the venting position.

(30) It can be seen that both compressed-air systems 1 at least in respect of the venting function and preferably also in respect of the aerating function have a two-channel design. The load V can therefore be aerated redundantly and also vented redundantly. The redundant aeration possibility above all is of particular significance, since it ensures that the compressed-air system 1 corresponds to the applicable high safety standards. Even if one of the working valves 2 or 3 should fail, so that one of the two aeration channels 24, 25 fails, one aeration channel 24 or 25 still remains for reliable venting of the load V.

(31) From a safety-related point of view it is also significant here that the venting cross-section for a compressed air venting flow enabled in the venting position by each working valve 2, 3 is greater than the maximum aeration cross-section that can be enabled in the aerating position. The easiest way to achieve this is for the internal valves channels of the working valves 2, 3 to be dimensioned differently and for the valve channel responsible for the aerating flow to have a larger cross-section than the valve channel responsible for the aerating flow. Of course the adaptation to various flow sections can also be performed at another point in the channel section of the compressed-air system 1 used for aeration and/or venting.

(32) The compressed-air system 1 is preferably used for aerating the load V so that both working valves 2, 3 assume their aerating position at the same time. If now as a result of a malfunction or damage one of the working valves 2, 3 should inadvertently switch over the venting position or inadvertently stick in the aerating position, then the one working valve 2 or 3 that has switched over to the venting position, because of the larger aeration cross-section, ensures ventilation of the load V, even though via the aerating working valve compressed airalbeit with a lower flow rateis being supplied. Thus the load V can switch off for safety reasons until the fault has been cleared. This ensures that the load V is not operated with just one functioning working valve 2 or 3.

(33) The purpose of the separating device 15 is to enable, without interrupting aeration of the load connection 14 and consequently of the load connected to it, a test procedure to test for the correct functioning of the working valves 2, 3. In such a test procedure, based on the operating state just described, in which the two working valves 2, 3 assume the aerating position, initially separate the first working valve 2 and then the other working valve 3 is separated via the separating device 15 from the load connection 14 and from the respective other working valve 3, 2 and in this fluidically separated state examines it for its switching function. Despite the separation of one of the working valves 2, 3 the load V will continue to be supplied with sufficient compressed air here, because its connection to the working valve 2, 3 not separated by the separating device 15 is open.

(34) In the compressed-air system 1 illustrated in FIG. 1, the separation of one or other of the working valves 2, 3 can be brought about simply by the working valve 2, 3 being switched over to the venting position. In this way at its working connection 7 and at the assigned input connection 16 or 17 a drop in pressure is prompted, causing the control valve member to switch over to a separated position, in which the channel section, in which the working valve 2, 3 switched over to the venting position is inserted, is unpressurised.

(35) In the compressed-air system 1 illustrated in FIG. 2 the separation in a fluid-tight manner or decoupling of the desired working valve 2, 3 takes place by a controlled remote operation of the multi-position valve 15b. The multi-position valve 15b contains at least one control valve member 34 that can be switched over in the course of a switchover movement 35 between various switching positions and can in this way be positioned, apart from in the already mentioned neutral position, in two different separated positions as well. For practical purposes the neutral position is located between the two separated positions, so that the switching over between the two separated positions is subject to the neutral position being adopted for at least a brief time.

(36) In the first separated position, in which the multi-position valve 15b in FIG. 2 has moved to the left, the working connection 7 of the first working valve 2 is as before in fluid communication with the load connection 14, while the second input connection 17 and therefore the working connection 7 of the second working valve 3 is separated from both the load connection 14 and from the working connection 7 of the first working valve 2 in a fluid-tight manner. In the second separated position of the multi-position valve 15b, in which the multi-position valve 15b or its control valve member in FIG. 2 has moved from the neutral position to the right, there is a fluid communication between the working connection 7 of the second working valve 3 and the load connection 14, while the first working valve 2 or its working connection 7 is separated from the load connection 14 and from the second input connection 17 and therefore from the second working valve 3 in a fluid-tight manner.

(37) This switching function can be implemented particularly easily with the help of a multi-position valve 15b, designed according to the exemplary embodiment as a 3/3-way valve. It is preferably a case of a valve where the neutral position is a stable basic position, which is preferably a mid-position, maintained by spring means 36. On this basis, the multi-position valve 15b can for practical purposes be deflected in a monostable manner optionally to the first working position or the second working position, which is possible with the help of two electrically operable drive devices 37 assigned to the multi-position valve 15b. Each of the two drive devices 37 is connected via an electrical control line 37a, 37b to the electronic controller 26 and if necessary can be activated and deactivated by this. The drive devices 37 are preferably of one of the designs as explained using the drive devices 27, 28 of the working valves 2, 3. Electromagnetic drive devices 37 or electrically operable pilot valves are preferably involved. The multi-position valve 15b can be of the directly electrically operable design or also of an electro-pneumatically piloted design.

(38) Each working valve 2, 3 has switching function examination means 38 assigned it, able to examine the correct switching function of the relevant working valve 2, 3. The switching function examination means 38 are implemented in the form of any suitable detection means or sensor means. In the exemplary embodiments two possible types of such switching function examination means 38 are shown, which as pictured can be present at the same time as or as an alternative to each other. These consist on the one hand of position detection means 38a, which respond to the positional change of the valve member 8 of the assigned working valve 2, 3 taking place during a switchover valve, respond and using a position detection of the valve member 8 are able to determine if the relevant working valve 2, 3 has correctly switched over or not.

(39) Another kind of switching function examination means 38 are pressure detection means 38b, which respond to a change in pressure in the fluid pressure present, upon switchover of the assigned working valve 2, 3, at the working connection of this working valve 2, 3. The pressure detection means 38b are preferably directly connected to the working connection 7 or to the assigned first or second communication channel 22, 23. The pressure detection is based on the fact that the air pressure prevailing at the working connection 7 in the aerating position of the working valves 2, 3 is considerably higher than in the venting position.

(40) Via electrical signalling lines 39a, 39b the switching function examination means 38 of the two working valves 2, 3 are connected by means of electrical signals with the electronic controller 26.

(41) The separating device 15 is for practical purposes equipped with self-function examination means 42, with which the correct switching function of the fluid engineering separating device 15 can be examined. These self-function examination means 42 are also preferably sensor means of any suitable kind. In the exemplary embodiment only the multi-position valve 15b is equipped with such self-function examination means 42, so that the compressed-air system 1 illustrated in FIG. 2 in terms of the intrinsic safety examination is of a higher quality than the less expensive compressed-air system illustrated in FIG. 1.

(42) The self-function examination means 42 can for example be position detection means 38a, which respond to the change in position when the control valve member 34 switches over and which are in particular able to detect if the multi-position valve 15b upon receipt of an appropriate control signal correctly switches over or has correctly switched over to the first or the second separated position. The self-function examination means 42 are preferably similarly connected by means of at least one electrical signal line 42a to the electronic controller 26.

(43) The compressed-air system 1 allows, while retaining the two-channel intrinsic safety, an examination of the functional capability of the two working valves 2, 3 without adversely affecting the aeration or compressed-air supply of the load V connected to the load connection 14.

(44) The working valves 2, 3 are functionally examined alternately, in an operating state of the compressed-air system 1 in which the working valve 2, 3 to be examined is decoupled from the load connection 14 and from the other working valve 3, 2 in the aerating position in a fluid-tight manner. Such an operating state can be specified by means of the separating device 15, by this being switched either over to the first separated position or the second separated position.

(45) The actual functional test procedure consists of the separated working valve 2, 3, in the abovementioned sense, in the course of at least one test operation activity being switched from the aerating position assumed up to that point over to the venting position. With the help of the assigned switching function examination means 38 this allows verification of a correct switchover. The position detection means 38a establish here if the valve member 8 is switching and/or has switched over. The pressure detection means 38b verify the correct switchover procedure on the basis of the fluid pressure present at the working connection 7, which for a correct switching function must drop to atmospheric pressure, if the assigned working valve 2, 3 has switched over to the venting position. After the test operation activity, the working valve 2, 3 tested is switched back to the aerating position again, so that then the other working valve 2, 3 can be examined in a corresponding way. The working valve 2, 3 not currently in test mode and not separated makes the compressed air necessary for its operation available to the load V.

(46) Since with the compressed-air system 1 from FIG. 1 the switchover of the separating device 15 is caused directly by the switchover of one of the working valves 2, 3 to the venting position, this switchover procedure of the relevant working valve 2, 3 is directly used here as a test operation activity. In the compressed-air system 1 from FIG. 2, however, the test operation activity of a working valve 2, 3 is only triggered once the multi-position valve 15b has switched over to the corresponding separated position.

(47) A test cycle is preferably developed in each case which first separates the first working valve 2 and the second working valve 3 by means of the separating device 15 from the load connection 14 and from the respective other working valve 3, 2, wherein the respective separated working valve 2, 3, while the working valve 3, 2 not separated remains connected with the load connection 14 maintaining the aerating position, is switched over in the course of a test operation activity to the venting position and the correct switchover is verified with the help of the switching function examination means 38.

(48) Through a rapid switchover of the separating device 15 pressure drops at the load connection 14, which could adversely affect the operation of the connected load V, are avoided without problems. There is also an advantageous possibility, however, of connecting a buffer capacity to the output connections 18 of the separating device 15 and consequently to the load connection 14, which in the event of any short-term interruption in the aerating flow caused by the switchover of the separating device 15 maintains the required compressed-air supply of the connected load V. This buffer capacity is preferably normally supplied with compressed air from the load connection 14.

(49) With the compressed-air system 1 of FIG. 2 there is the advantageous possibility, before testing the two working valves 2, 3 of examining the separating device 15 for its part for correct functional capability. It is preferably part of each examination cycle that prior to examining the two working valves 2, 3 the functional capability of the separating device 15 or of the multi-position valve 15b is examined. To this end, the multi-position valve 15b, starting from the neutral position illustrated in FIG. 2, is switched over to the first separated position and then back again to the neutral position, and then to the second separated position and back again to the neutral position. The functional test of the multi-position valve 15b takes place when both working valves 2, 3 assume the aerating position, so that the two-channel capability is guaranteed.

(50) Only once it has been verified that the multi-position valve 15b is functioning correctly, does a selective testing of the two working valves 2, 3 takes place, wherein again the two-channel capability is guaranteed.

(51) The functional testing of the separating device 15 takes place using the self-function examination means 42 described above.

(52) With both compressed-air systems 1 it is advantageous if the working valves 2, 3 can be examined for the complete valve lift, in order to reach a reliable conclusion on the functional capability, without adversely affecting the aeration of the load V.

(53) A reliable venting can also be adversely affected by the fluid flow through the aeration channel 24, 25 being hindered, for example due to a blocked silencer 12. In order to also be able to perform an examination in this regard, it is advantageous if each working valve 2, 3 is assigned a control air reservoir 43, 44 shown by a dot-dash line in FIG. 2, filled with compressed air, before the relevant working valve 2, 3 is switched over to the venting position and which in the venting position of the relevant working valve 2, 3 can be via this working valve 2, 3.

(54) By way of example, each working valve 2, 3 is assigned its own control air reservoir 43, 44, which is in constant fluid communication with the working connection 7, in that in the exemplary embodiment it is connected to the first or the second communication channel 22, 23. Consequently the control air reservoir 43, 44 is always filled with compressed air and kept full, if the assigned working valve 2, 3 is in the aerating position. If for a test activity the separated working valve 2, 3 is switched to the venting position, the air volume contained in the assigned control air reservoir 43, is vented via the working valve 2, 3 in the venting position. This venting flow is detectable by detection means shown by a dot-dash line and can be evaluated by the electronic controller 26, to which the detection means 45 are for practical purposes electrically connected. The detection means 45 are in particular designed so that they can detect a time-dependent pressure change or a flow of the compressed air venting flow from the control air reservoir 43, 44. From a comparison with stored reference values it is then possible to determine if the venting time is too long in comparison with a correct venting time, allowing a blocked silencer or similar to be concluded. With the help of a flow sensor it can be directly verified if the flow rate of the venting flow is still sufficiently high or if it has dropped, which similarly indicates a blockage.

(55) In an exemplary embodiment not shown the working connections 7 of the two working valves 2, 3 are connected to a common control air reservoir 43, 44, wherein through suitable valve technology it is ensured that the two working connections 7 do not interfere with each other.

(56) In a departure from the exemplary embodiment there is the possibility of further developing the working valves 2, 3 so that on the output side, apart from the working connection 7 they also have a further in this regard separate filling connection, which alternately with the working connection 7 is connected with the compressed air source P or with the atmosphere. In this case the control air reservoir 43, 44 in the aerating position of the assigned working valve 2, 3 is vented and in the venting position of the working valve 2, 3 aerated, that is to say filled. This takes place for practical purposes with a control air reservoir assigned jointly to the two working valves. The correct penetrability of the silencer 12 is therefore always checked if the working valve 2, 3 switches to the aerating position and in doing so vents the assigned control air reservoir. Needless to say, in this case the detection means 45 are integrated into the channel system so that the compressed air venting flow can also actually be detected.