fully populated with outlets 20 which as shown in fig2 b outlets 20 are preferably circular but it is understood that the individual outlets can have non circular configurations the number and size of the outlets are designed to achieve the desired steam flow rate and velocity the size of the outlets 20 should be sufficiently small to minimize the amount of fibers and other debris from the sheet of material being heated that enters into the discharge chambers nevertheless in operation as steam is applied through the perforations 20 onto a moving sheet of paper for instance the middle of front screen segment 31 can come into contact with the sheet in this regard it is may be preferred to avoid excessive blank areas on the middle of front screen segment since there may be a tendency for debris to accumulate in areas on the panel that are not populated with outlets as is apparent the number of front screen panel segments 31 required to cover a steam distribution apparatus will depend on the total cross directional length of the steam distribution apparatus and the cross directional length of each panel segment 31 each pneumatic actuator 32 is operatively connected to a pipe 42 which has an inlet end located within the header 36 and an outlet end that is located in a.