in the attached diagram there is schematically shown the course of the fluid level n in a pump sump as well as the threshold values of the applied pumps over the time t . the lower unbroken line 2 represents the fluid level in the pump sump over the time t . the unbroken line 4 , the dashed line 6 as well as dot - dashed line 8 in each case symbolise the fluid level threshold value of a pump at which the respective pump is activated . in its basic condition each pump has three fluid level threshold values s 1 , s 2 and s 3 . at the same time the threshold value s 2 corresponds to an initial threshold value which is set in the basic or delivered condition of the pump and when it is reached the pump is activated via a level sensor . the threshold value s 1 is the threshold value which when reached deactivates the pump . the threshold value s 3 represents a second start threshold value at which when reached each pump is in any case activated , independently of the remaining control . s 3 is thus an emergency start value at which the pumps in any case are activated , for example if the supply of fluid in the pump is so large that an individual pump is no longer sufficient to pump away the fluid . hereinafter the control of three pumps over a temporal course in a common pump sump is described . a common pump sump may at the same time be seen as an arrangement of several pump sumps which for example communicate with one another via tube conduits . at the beginning all three applied pumps are set in the condition of delivery , i . e . the fluid level threshold value is set to the initial threshold value s 2 . due to tolerances and height differences on application into the pump sump however with a large probability not all initial threshold values lie exactly at the level s 2 . with the rising of the fluid level in the pump sump thus firstly the fluid level threshold value of one of the three pumps , in the shown example that pump which is represented by the unbroken line 4 is reached . on reaching the fluid level threshold value 4 at the point in time t 1 the corresponding pump is set in operation and the fluid level 2 in the pump sump falls . the fluid level threshold value of the two further pumps is thus firstly not reached so that these pumps are not set into operation . at the point in time t 2 the fluid level 2 reaches the threshold value s 1 at which the first pump is set out of operation . at the same time the fluid level threshold value of the first pump is set by the control to the value s 3 and thus firstly blocks the first pump . furthermore the control of the first pump sets its counter n for the number of pumps arranged in the pump sump in operation to the value n = 1 . in this condition the fluid level threshold values of the two further pumps continue to correspond to the initial threshold value . the fluid level 2 in the pump sump now increases again until reaching the fluid level threshold value of the second pump which is shown in the diagram by the dashed line 6 . on reaching this threshold value the second pump is set into operation ( at the point in time t 3 ) and the fluid level reduces again until the threshold value s 1 is reached at the point in time t 4 and the second pump is switched off . during the running of the second pump the first pump ( unbroken line 4 ) detects that the fluid level 2 in the pump sump reduces whilst it itself is not in operation . if now by operation of the second pump at the point in time t 4 the fluid level 2 reaches the threshold value s 1 and the first pump registers this , its control increases the counter n by 1 in the present case thus to n = 2 . the first pump simultaneously reduces the fluid level threshold value of the first pump . with this it reduces the threshold value to a value above the initial threshold value . the new fluid level threshold value lies above the initial threshold value s 2 by δs 1 , therein δ ⁢ ⁢ s 1 = ( s 3 - s 2 ) × 1 n the new fluid level threshold value is thus s 2 + δs 1 . the second pump after its running at the point in time t 4 sets the fluid level threshold value of the second pump ( dashed line 6 ) to the threshold value s 3 . if now after the point in time t 4 the fluid level 2 in the pump sump rises again and reaches the initial threshold value s 2 , the third pump is activated at the point in time t 5 , whose fluid level threshold value ( dot - dashed line 8 ) again corresponds to the initial threshold value . the third pump now pumps fluid for so long until the fluid level 2 has reached the threshold value s 1 at the point in time t 6 . if the fluid level 2 reaches the threshold value s 1 , the third pump is switched off at the point in time t 6 . simultaneously the control of the third pump sets the fluid level threshold value of the third pump to the value s 3 , wherein the third pump is blocked as previously the first and the second pump . furthermore the control of the third pump according to the preceding pumps sets its counter n for the number of pumps to the value n = 1 . during the running of the third pump between the points in time t 5 and t 6 , as previously described , the first and second pumps detect that the fluid level 2 changes by operation of a further pump . the controls may detect this in that the fluid level 2 changes before the respective fluid level threshold value of its own pump has been reached . this causes the control of the first pump at the point in time t 6 to increase the counter n for the number of pumps again by 1 to the value n = 3 . accordingly the control of the second pump increases its counter n to the value n = 2 . the control of the first pump again reduces the fluid level threshold value at the point in time t 6 again to the value thus the new fluid level threshold value of the first pump is s 2 + δs 2 , wherein δs 2 =( s 3 − s 2 )× 1 / n . the control of the second pump , like the control of the first pump at the point in time t 4 , reduces the fluid level threshold value of the second pump to the value δs 1 above the initial threshold value s 2 . thus at the point in time t 6 the fluid level threshold value of the first pump ( unbroken line 4 ) is the lowest so that with a further increase of the fluid level 2 in the pump sump firstly at the point in time t 7 the fluid level threshold value of the first pump is reached and the first pump is again set into operation . the first pump then again reduces the fluid level 2 , until at the point in time t 8 the threshold value s 1 is reached and the first pump is switched off . at this point in time the control means of the first pump sets the counter for the number of pumps again to the value n = 1 and increases the fluid level threshold value of the first pump again to the value s 3 . simultaneously the control of the second pump increases the counter n to the value n = 3 and the control of the third pump increases its counter n to the value n = 2 . accordingly the fluid level threshold value of the second pump is reduced to the value s 2 + δs 2 and the fluid level threshold value of the third pump to the value s 2 + δs 1 . thus at the point in time t 8 the fluid level threshold value of the second pump is the lowest so that this after a renewed increase of the fluid level 2 at the point in time t 9 is activated as the next pump . according to this , the method according to the invention runs cyclically further , wherein the individual pumps , i . e . in the described example the pumps 1 , 2 and 3 are always activated alternately in succession . this leads to a uniform burdening of the pumps . although the example has been described for three pumps , any other number of pumps is possible . the control of the individual pumps is identical , wherein according to the method according to the invention , independently of the number of pumps and without linking the individual pumps an alternating operation of the pumps sets in , irrespective of how many pumps are arranged in the pump sump . if a further or new pump is additionally applied into the pump sump , its fluid level threshold value again has the initial threshold value s2 which is always smaller than the fluid level threshold value of the already operated pumps . this results from the fact that the amount is δ ⁢ ⁢ s n - 1 = ( s 3 - s 2 ) ⁢ 1 n wherein n corresponds to the number of previously run pumps . thus on applying a new pump this pump is always firstly activated with an increase of the fluid level 2 . the above described cycle then again automatically sets in . accordingly the pumps react if one of the pumps should fail : if for example at the point in time t 6 the first pump should fail , the next pump which is activated with an increase of the fluid level 2 is the second pump , since this has the next highest fluid level threshold value . subsequently according to the method according to the invention an alternating operation of the second and third pump automatically sets in . the method according to the invention by way of an intelligent control specific to the pump ensures that with a failure of a pump or with the addition of a further pump an alternating operation of the pumps in the pump sump automatically sets in . at the same time there is no direct communication between the pumps or a common central control of the pumps . each pump represents a unit closed per se which merely need to be connected to a fluid conduit and a current supply . the control means and the switch of each pump , preferably a pressure sensor are preferably integrated into the pump housing so that the individual pumps may be simply suspended into a pump sump as with conventional submersible pumps . the pump according to the invention may also be applied on its own in a pump sump . for this the control of the pump is preferably designed such that it recognises this condition of application of the individual pump . this may for example be effected in that the fluid level in the pump sump after the running of the pump increases beyond the value this is the fluid level threshold value at which a further pump in the pump sump must start . if the fluid level rises beyond this value this is a sign that no further pump is present . in this case the control of the single present pump may reduce its fluid level threshold value at which the pump is activated again to the initial threshold value s 2 or to the value this has the advantage that the value s 2 remains as an emergency start threshold value , wherein the corresponding fluid level in the normal case should not be reached . on reaching s 2 every present pump is in any case activated or switched on independently of the remaining control method . while the method herein described , and the form of apparatus for carrying this method into effect , constitute preferred embodiments of this invention , it is to be understood that the invention is not limited to this precise method and form of apparatus , and that changes may be made in either without departing from the scope of the invention , which is defined in the appended claims .