The press headbox must have a minimum flow to ensure good
distribution of the pulp across the width of the press. The specific flow is dependent
on the size of the orifices installed between the headbox and the body of the press.
Operating below this flow encourages pulp to stop moving at points of more
resistance, such as along the ends of the press by the end seals. This begins to form
stagnant pulp areas that will dewater, act as brake shoes causing undesired torque, take
up space that would otherwise be available for washing pulp, and will be difficult to
dislodge again without lowering the vat.