A web forming apparatus of the above type is prior known e. g. from our Finnish patent application No. 982539. In this prior known apparatus, the water-receiving chambers set behind the wire are provided with dewatering elements. It is an object of the present invention to provide an effective and simple alternative solution to this dewatering system.

An apparatus of the invention is characterized in that each receiving chamber is connected to at least one substantially vertical pipe, the mounting thereof being such that vertical drops between the pipe's top and bottom end are sufficient for developing a gravitational tube leg in the pipe in which the water is flowing.

A second characteristic feature of the invention is that the amount of water flowing from each water receiving chamber is measured and adjusted for achieving a uniform formation of pulp web in a wedge-shaped space defined by wires.

A third characteristic feature is an orifice strip for delivering water therethrough from a water receiving chamber into a vertical discharge pipe, as well as a compensating circulation for discharging a small amount of water from a water receiving chamber from the side opposite to the discharge pipe. Said perforated strip and said compensating circulation

provide for a consistent draining of water from the web across its entire width.

The inventive measuring of the amount of water discharging from a pulp web can be implemented preferably in such a way that the water discharging vertical pipe terminates in a water receiver provided with at least one recess constituted by a sluice element, through which water discharges from the receiver in the form of a sluice flow, said flow being measured by means of a sluice flow meter. The measurement is a simple process, nor is it disturbed by possible impurities, such as air bubbles present in the liquid. It is obvious for a skilled person that the inventive measuring of discharging water can be implemented just as well by other, prior known methods.

As for an apparatus of the invention, it is essential that the vertical drop between the ends of a water discharging pipe be in such a magnitude that the pipe develops a sufficient gravitational tube leg. The vertical drop is preferably 4-10 m.

The invention will be described in more detail with reference to the accompanying drawing.

Reference numeral 1 represents a web forming unit, comprising wire elements which establish a wedge-shaped space, the suspension stock being fed into said wedge-shaped space. On the opposite side of the wire are dewatering boxes, comprising several, for example six boxes, both above the top wire section and below the bottom wire section.

From dewatering boxes 2 present in the web forming unit 1, water is passed through orifice strips 3 along pipes 4 and 5 for further processing. These pipes 4 and 5 comprise a comparatively lengthy, substantially vertical section, the purpose of said sections being to function as suction pipes, i. e.

to establish a so-called suction leg. As a result of a major vertical drop, a gravitational tube leg is developed by water in the flow pipes for replacing a traditional vacuum pump system on the wire section of a drying machine. It should be noted that the flow rate must be sufficiently high, normally in excess of 2 m/s, for water-entrained impurities like air bubbles and gas bubbles and others to be carried along with the flow instead of becoming deposited e. g. in the upper elements of the apparatus.

A minor amount of water, normally about 10%, is discharged along pipes 6 and 7 from the web forming unit 1 from the side opposite to the pipes 4 and 5. This results in a consistent dewatering across the entire width of a pulp web.

In the web forming unit 1, pressures are measured both on the side of a pulp web and on the side of dewatering boxes. In the dewatering boxes, the pressure is measured both at the ends close to the discharge pipes 4 and 5 and at those close to the discharge pipes 6 and 7.

The discharge pipes 4,5,6 and 7 are provided with valve elements for regulating a flow in the pipes.

The discharge pipes 4,5,6 and 7 terminate in a water receiver 8, which functions as a water trap. This receiver 8 is provided with at least one recess 9, which is positioned and dimensioned such as to establish a sluice element for the water mass accumulated in the receiver 8. As the dimensions of the recess 9 and flow characteristics of water are known, the flow rate can be determined as based on the height of a liquid level flowing in the recess.

According to this height, it is now possible to adjust draining of water as desired from each dewatering box.

In the illustrated solution, the receiver 8 is circular in cross-section, said receiver having its middle section provided with a separate water tank for delivering the sluice flow therein.

The water draining from the receiver 8 in the form of a sluice flow is delivered by means of a pump in a continuous flow along a pipe 10 for further processing.

In the present example, each dewatering chamber 2 is provided with the water discharge pipe 4 and 5, as well as with the extra water discharge pipe 6 and 7 for a balanced dewatering process. It is obvious that the number of discharge pipes can always be varied as necessary without departing from the scope of the invention.

The inventive solution is simple, inexpensive, and effective regarding its implementation. The amount of water to be drained being adjustable specifically in terms of each dewatering chamber and the uniform drainage of water across the entire width of a pulp web improve the pulp web in terms of its quality and uniformity. The suction effect created by a vertical drop increases significantly the capacity of a pulp web former and this augmented capacity is achieved without having to use suction pumps which are expensive in terms of investment and operating costs. Measuring the amount of draining water by means of a sluice level, described as one conceivable implementation, constitutes an inexpensive, accurate, and reliable implementation.