pump p 20 the line a 2 on the pressure side of the pump p 20 is connected to the hydrocyclone plant 20 to form the feed of its first centrifugal cleaning step 20 a 1 in the embodiment of fig2 b the hydrocyclone plant 20 situated in the short circulation of the paper machine includes centrifugal cleaning steps 20 a 1 20 a 2 and 20 a 3 an accept line a 3 leads further from the first hydrocyclone i e the centrifugal cleaning step 20 a 1 of the hydrocyclone plant 20 into connection with a stock line b 1 of a second stock chest 10 a 2 in the embodiment wire water from the paper machine is passed to a wire pit 110 through a line d 1 which wire pit 110 in this embodiment is formed by a planar wire pit structure a so called flume which comprises a horizontal flow path for wire water said wire pit 110 removes effectively air in bubble form from the wire water and pre deaeration of the wire water is accomplished by means of said wire pit type the wire water is passed from the wire pit 110 through a discharge line d 2 and a pump p 30 to a deaeration tank 13 a 3 from which there is further a discharge line f 3 leading into connection with the line b of the stock m 2 of the second stock chest 10 a 2 via a mixing device 12 the line f 4 leads further from the discharge line f 3 of the deaeration tank 13 a 3 into connection with the line a 1 of the stock m 1 of the.