Wet suction boxes

The more the fibre network grows, the more difficult it will be to drain the stock. A way to Overcome the increasing drainage resistance is to gather the foils in closed boxes and to let them work in a vacuum.

The underpressure between the foils makes the suction pulses longer and more water is sucked
through the fibre net.

The vacuum in the suction boxes is increased keeping step with the growth of the fibre network.
When the wire has passed the last suction box, the free stock is in most cases gone and the water mirror on the wire has disappeared. This point is called the wet line. All fibres are now fixed in the fibre network and the forming is in principle finished.