diameter of the pinholes 25 is too small the lubricant preferably an aqueous fluid in the pressure chamber 10 cannot even at a high pressure of 20 to 50 bar flow through them or the flow is too slow for good lubrication field tests determine a suitable size for the pinholes of the pressure balancing diaphragm 20 and the rigidity thickness of the diaphragm 20 so that water can filter through the diaphragm in such a manner that the diaphragm still serves as a sealing the pressure of the fluid in the pressure chamber 10 is generally in the range of 20 to 100 bar when the web 8 is transported if the diameter of the pinholes 25 is too big the lubricant exits the pressure chamber and the necessary pressure is not maintained in the pressure shoe 3 to prevent the pinholes 25 from being blocked a filter not shown can be used to prevent small particles from entering the pinholes the shape of the pinholes 25 can vary they may be round oblong elongated rectangular etc their number and arrangement for instance into different patterns can also vary the pinholes 25 are made using electron beam cutting or laser cutting the pinholes 25 can be made using for instance the micro edm micro electro discharge machining system model 82 of panasonic with which it is.