and 13 show the valve 10 adapted to be opened at a certain pressure to initiate the release of gas contained in chamber 12 and thereby forcing out fluid contained in chamber 11 to perform a cleaning operation of tracer chamber 9 connection 22 pantograph 6 and gland plate 7 this arrangement is similar to the hydraulic system 3 as previously described the tracer chamber 9 with the tracer container shown schematically is shown in fig3 sections 1 to 3 fig4 a shows on a further enlarged scale the lever arms pantograph 6 with the gland plate 7 in an extracted position i e the gland plate 7 being forced into abutment with the well wall 16 lever arms 26 are hinged to a supporting structure 27 of the gland plate 7 by a pivotal connection and to a mounting portion 27a of the body of the injector further the supporting structure 27 is connected to the piston 25 in cylinder 5 by means of piston rod 18 and pivotal connections the tracer is transported from the tracer chamber 9 via the connection 22 in the injector wall and further via a tube or hose 24 and through a bore 29 in the gland plate 7 as shown in fig4 b and c the gland plate 7 is adapted to fit the wall in the bore hole well casing and is provided with a packing 30 to obtain a tight connection when in abutment with the wall as will be seen in fig4 c the gland plate 7 is connected to the.