inch or less and thus the pressure drop across the web is one to a few thousand psi per inch the effect of the rapid expansion of air as it passes through the web 26 is to remove water from the web a prior art air press device used on a tissue web having a solids content of about twenty five percent and a thickness of about three hundredths of an inch was able to increase the solids content to approximately thirty three percent while these levels of water removal are desirable the mechanical lever employed in the prior art device to urge the pressure box against the web can result in web breakage in the event of pressure loss although the precise mechanism is not clearly understood the use of pressurized air is more effective than vacuum alone because of the higher pressures available and the greater air volume forced through the web prior art air presses have two basic problems establishing an adequate seal between the pressure box and the forming fabrics without causing excessive wear of the forming fabrics and controlling the loading of the pressure box against the fabric a pressure of twenty psi with an area of six inches by 200 inches results in a force of 12 tons caused by the pressure in the box which must be counterbalanced if a mechanical lever arm is used to allow movement of the.