in blow through rates and differential pressures between the two methods represents great savings of energy steam and control functions in fact the prior art method is completely unworkable at a steam input pressure between about 0 psi and 15 psi gauge although the utilization of velocity pressure control of blow through alone provides substantial improvements in control response range of pressure control and energy conservation it is still inadequate for the needs of drying systems at 0 psi input pressure in the above example a differential pressure of 4 psi in the dryers is still required and a further 2 to 3 psi pressure drop occurs in the piping and apparatus through which the blow through steam must pass if it is to be recirculated accordingly the bleed steam must flow from a vacuum of 6 to 7 psi to a condenser maintained at even lower pressures the prior art bleed valve 45 see fig3 must be quite large to pass sufficient bleed steam at such low pressures with minimal pressure drop and all of the bleed steam is wasted at any other pressure 20 psi for example the pressure drop imposed on the bleed valve 45 is multiplied many times at the same.