its width the jet pipe may divided into any number of compartments as desired through each compartment a desired quantity of medium flow per meter of doctor width per unit of time is produced in this manner by regulating the quantity of lubricating medium it is possible to equalize the wear of the doctor blade 11 i e by increasing the amount of lubricant at the portion s of the width of the doctor blade at which the most intensive wear has been noted fig2 c is a cross sectional view of the jet pipe 12 the jet pipe 12 comprises a frame mantle 12a having jet nozzles 12b 1 12b 2 partition walls 12c 1 12c 2 and end walls 12d 1 12d 2 arranged therein the partition walls are arranged in the interior of the jet pipe while the end walls define an enclosed interior space within the jet pipe by positioning a desired number of partition walls the interior of the jet pipe 12 is divided into the compartments g 1 g 2 and g 3 the lubricant duct 13a 1 passes into the compartment g 1 the lubricant duct 13a 2 passes through compartment g 1 into the compartment g 2 and the lubricant duct 13a 3 passes through compartments g 1 and g 2 into the compartment g 3 as the lubricating medium preferably water is used other.