in the fixed position clamping straps 21 22 23 25 can be metallic whereas the t shaped connection member 24 can be made out preferably of a corrosion resistant synthetic plastic material suitable for operation underground and with minerals being or of stainless steel the end of plastic tube 20 overlaps the connection nipple of a nozzle receiving member 26 the clamping strap 25 is arranged at the end of tube 20 which end receives an axial projection 30 formed on the nozzle receiving member 26 thus clamping strap 25 clamps the tube 20 on the nozzle receiving member as can be understood the conduit system according to the invention can be easily exposed for cleaning or repair merely by removing sheet like strips 14 and without disassembling of one or more plastic tubes after required cleaning or repair cover strips 14 can be again mounted to their closed position in the system of the invention therefore no components subjected to corrosion are used the cover strips 10 14 can be clamped to the blade by any suitable means the cover strips 10 14 can be formed not only as sheet like strips but also made out of a profile iron or made of segments a shown in fig4 b furthermore it is possible to connect the cover strips 10 14 to the blade 2 or locking ring 4 by a hinge 27 as shown in fig4 a so that they can swing to and from the blade or locking ring it is to be understood that similar fluid distribution circumferential passages as well as radially extended bridging passages are provided in the side wall of the blade 2 and.