A pressurized box (28) is positioned opposite a vacuum box (30).

The pressure box and opposed vacuum box form an air press.

It is the air volume (Q) having permeated the felt (H) via a suction surface of the UhIe box over the area (A) of the UhIe box and vacuum (Δp) being across the felt.

The liquid is sucked through a transverse slot communicating with a sucking box (110, 125).

In the method according to the invention, based on air volume (Q) of a UhIe box (11), an area (A) and vacuum (Δp) of the UhIe box, an air permeability index (K) of the felt (H) is calculated.

Under the forming box (1) a forming wire (3) and a vacuum box (5) is placed.

The invention renders it possible to manufacture foils and vacuum box covers cost-effectively.

The trailing cross machine direction baffle is positioned over a vacuum box which prevents air from leaking around the trailing baffle.

Wear indicators (80) are formed in the seal strips (52, 54) of a suction box (44) of a suction roll assembly (15) of a papermill.

The suction box (4) has a circular cylindrical cross section and it is arranged to remain stationary while the roll shell (2) rotates.

The apparatus comprises a suction box (4) and a superjacent forming head and a forming wire (2) placed in between.

On the suction surface of the suction box a belt (18) that is displaced in the sheet transport direction (13) of the sheet is disposed.

A curved suction box apparatus (34) is disclosed for guiding a web (W) towards a nip (N) of a nip press (32).

A vacuum box draws air through the forming fabrics and the web, from the pressurized box increasing the total pressure gradient accross the web to 0.1 to 0.2 MPA (15 to 30 PSI) or more.

The suction roll comprises a suction box (11) and therein axial seals (12a1, 12a2), which have been fitted in grooves (U1, U2) in a holder part (14).