Note! If the air flow to the drying sections is restricted by means of sluice gates, the air flow must also be throttled at the suction side of the heater blower in order to prevent the positive pressure in the inlet air channel end of a positive pressure heater, or correspondingly, the vacuum at the outlet air channel of a vacuum dryer, from grow too high. The shutters of the air channels must be provided with open-closed stickers as a reminder of their operating positions for the later times of use.