[ 0038 ] fig1 shows a schematic diagram of a filter testing device 10 according to a preferred embodiment of the present invention . the filter testing device 10 includes the switching valves v 1 through v 5 and a proportional valve v 6 . furthermore , the filter testing device 10 includes external connections , where the external connections include a compressed air supply connection 12 through which compressed air is supplied in testing operation , a connection 14 for internal venting , a connection 16 for external venting , a filter connection 18 for connecting the filter and / or the filter device to be tested , and a connection 20 for an external reference tank 22 . an internal reference tank 24 is preferably present in the filter testing device 10 . the valves v 1 through v 5 are in mutual fluid connection through the connecting lines 26 . furthermore , the valves are in fluid connection with the respective internal connections via the connecting lines 28 . the internal reference tank 24 is in fluid connection with the valve v 2 and with the connection 20 for the external reference tank 22 via the connecting lines 30 . the valves v 1 - v 5 are preferably diaphragm valves and also preferably have a small valve volume v v1 - v v5 . the connecting lines 26 , 28 , 30 , the internal reference tank 24 , and the volumes v v1 - v v5 of the valves v 1 - v 5 are referred to below as internal volumes . furthermore , in the illustrative description of a preferred embodiment of the present invention given below , a filter testing device 10 which comprises only one proportional valve v 6 is described . furthermore , the filter testing device 10 preferably includes a pressure meter 32 . during the testing of a diaphragm filter , for example , the internal reference tank 24 is filled with compressed air of a certain pressure . during a following measurement , the size of the pressure drop in the filter is determined with the help of the reference tank 24 and the pressure meter 32 , and thus the quality of the filtered is determined . as part of this testing , the filter and / or the filter device to be tested is / are preferably also validated , i . e ., the quality of the filter is determined on the basis of predetermined and / or predeterminable standards . therefore , the testing device 10 is preferably connected to the contaminated side of the filter , i . e ., the side to which the fluid that is to be filtered is supplied . during the test , however , it frequently happens that unfiltered fluid , which is thus contaminated , enters the filter testing device 10 , in particular its internal volumes , through a return flow . however , for testing that is suitable for validation , it is necessary to ensure that the filter testing device 10 is not contaminated with bacteria or soiling before each new testing procedure . it is thus necessary to thoroughly clean the filter testing device 10 , preferably before each testing operation . furthermore , to permit even more reliable cleaning , the internal volumes are preferably defined as consisting of parts and / or lines which are made essentially completely of a high - grade steel or a material that conforms to fda requirements ( fda = u . s . food and drug administration ), for example , polytetrafluoroethylene ( teflon ™). the inventive cleaning method is described below with reference to the valve table shown in fig2 . the switching of the valves can be performed manually or automatically . in an interactive procedure , an operating person is preferably instructed to perform various actions , e . g ., connecting tubes to certain external connections , and then this is confirmed via an input device ( not shown ). in addition , the switching of the valves is preferably performed automatically according to a cleaning program that is to be selected . first , one or more internal volumes to be cleaned are selected from a plurality of internal volumes . this may preferably take place by way of an input ( not shown ). however , it is also conceivable for the selection to be made by manually switching the valves . in the cleaning process which is described below as an example , essentially all the internal volumes are selected and cleaned . a function check is then performed , preferably to check on whether there is an adequate operating pressure in a compressed air source ( not shown ). if it is found that there is an adequate operating pressure , then first a step of filling is performed , i . e ., flooding the selected internal volumes that are to be cleaned , namely all the internal volumes in the present case . to do so in the present case three paths are filled in succession with one cleaning fluid , which may be a suitable cleaning fluid as described below . initially , a cleaning fluid tank is connected via a pump ( not shown ) to the connection 14 for internal venting . the internal reference tank first is filled , i . e ., flooded . to do so the valves v 1 through v 6 are brought to the state z 1 shown in the valve table of fig2 i . e ., v 1 , v 4 , v 5 and v 6 are closed and v 2 and v 3 are opened . furthermore , a tube which is connected to or leads to a collecting , tank ( not shown ) is connected to the connection 20 for the external reference tank . then sufficient cleaning fluid is pumped into the filter testing device 10 until the fluid escapes again at the connection 20 for the external reference tank . as soon as this is detected , the pump is stopped . next , the path of the external venting , i . e ., the path which includes the valve v 5 and the connection 16 for the external venting , is filled , i . e ., flooded . the procedure here corresponds to that in filling , i . e ., flooding , of the internal reference tank 24 , but in this case a corresponding drain hose is connected to the connection 16 for the external venting and the valves are switched according to the state z 2 in the table of fig2 . then , in turn , enough cleaning fluid is added until it is found that cleaning fluid is escaping at the connection 16 for the external venting . then the pump is stopped again . next the filter connection 18 is filled , i . e ., flooded . to do so , the procedure followed corresponds to that for the two cases described above , i . e ., a hose is connected to the filter connection 18 and the valves are switched according to the state z 3 in the table of fig2 . the cleaning fluid is pumped into the filter testing device 10 until it is detected that the cleaning fluid introduced is escaping at the filter connection 18 . then the pump is stopped . when all the volumes that are to be cleaned have been filled , i . e ., flooded , all the valves v 1 through v 6 are closed ( state z 4 ). this state is retained for a predetermined and / or predeterminable period of time t1 to “ loosen ” the dirt present in the volumes that are to be cleaned , i . e ., to partially dissolve the dirt present in and / or adhering to the internal volumes and to treat the dirt by a chemical and / or biological reaction . the period of time t1 is preferably about 30 minutes , but the period of time t1 may also be set differently , e . g ., in accordance with the type of contamination present and the type of cleaning fluid used . after the period of time t1 has elapsed , the volumes to be cleaned are rinsed with a cleaning fluid which is always being replenished . the rinsing of the volumes that are to be cleaned preferably takes place at the same time , i . e ., all the internal volumes are rinsed at the same time . therefore , the valves are switched according to the state z 5 in the table in fig2 . the rinsing with cleaning fluid that is always being replenished is performed for a predetermined and / or predeterminable period of time t2 , which amounts to about 10 minutes in a preferred embodiment , i . e ., is preferably shorter than t1 . the drying of the rinsed internal volumes is described below . the drying is preferably performed with a stream of air at a certain pressure . the pressure preferably amounts to a relative pressure of about 1 bar , but a stream of air at any other suitable pressure may also be used . thus , a check is first performed to determine whether there is a sufficient air pressure in the compressed air source ( not shown ). if there is a sufficient air pressure , the step of drying the cleaned , preferably rinsed or filled , internal volumes is performed . the rinsed internal volumes are preferably dried in succession as described below . for drying the internal reference tank 24 , first a compressed air supply is connected to the connection 20 for the external reference tank 22 . the valves are then switched according to the state z 6 in the table of fig2 . then compressed air , preferably at approximately 1 bar , is introduced into the filter testing device 10 through the connection 20 for the external reference tank 22 . this state is maintained for a predetermined and / or predeterminable period of time t3 . after the period of time t3 has elapsed , the internal reference tank 24 is closed , i . e ., the valves are brought to the state z 7 and thus the valve v 2 is closed . with this step , cleaning of the internal reference tank 24 is concluded . for drying the internal venting comprising the valve v 3 and the connection 14 for the internal venting , first the compressed air supply is connected to the compressed air connection 12 . in a state z 8 , a sufficient pressure is built up in and / or for the proportional valve v 6 by switching the proportional valve v 6 to x %, i . e ., the pressure drop in the proportional valve v 6 amounts to between 100 % and 0 %. the valves are then switched one after the other according to the states z 9 through z 13 , i . e ., while the internal venting is drying , air flows out of the filter testing device 10 alternately through the connection 14 for the internal venting and through the connection 16 for the external venting . after a predetermined and / or predeterminable period of time t 4 has elapsed , the drying of the internal venting is concluded , and the valves are switched to the state z 14 and subsequently z 15 , i . e ., the internal venting is vented and the valve v 3 of the internal venting is closed . thus the drying of the internal venting is concluded . then the external venting , which comprises the valve v 5 and the connection 16 for the external venting , is dried and then the filter connection 18 is dried . to do so , the pressure connection of the compressed air supply remains connected to the compressed air connection 12 , the valves are switched to the state z 16 and compressed air of a predetermined and / or predeterminable pressure is passed through the filter testing device 10 , so that the air escapes at the connection 16 for the external venting and at the filter connection 18 . after a predetermined and / or predeterminable period of time t5 has elapsed , the drying of the external venting is concluded and the valves are switched to the state z 17 to then dry the filter connection 18 . in doing so , the path of the external venting is closed by closing the valve v 5 . then compressed air is again passed through the filter testing device 10 , with the air then escaping only at the filter connection 18 . after a predetermined and / or predeterminable period of time t 6 has elapsed , the drying of the filter connection 18 is concluded and the valves v 1 - v 6 are switched to the state z 18 . the cleaning process is thus concluded and the filter testing device 10 is now ready for use for the next testing operation . to reliably ensure the validation capability of the inventive filter testing device 10 , a so - called safety function is also provided in the filter testing device 10 in a preferred embodiment of this invention . in this embodiment , in the event of a premature termination of the drying process , a warning is output to the operating person , indicating that the cleaned filter testing device 10 does not have validation capability . such a warning is output with each test procedure until a proper drying has been conducted . the foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting . since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art , the invention should be construed broadly to include all variations within the scope of the appended claims and equivalents thereof .