Apparatus for damping pressure fluctuations in pulp suspension flow of paper machines

An apparatus for damping pressure fluctuations in the pulp-suspension flow of a paper machine includes a pipe system which delivers the pulp suspension to a headbox and in the interior of which the pulp suspension flows toward the headbox. A portion of the pipe system is surrounded by a gas, such as air, which is under pressure and which is situated within a suitable enclosure. This portion of the pipe system is formed at least in part by an elastic wall structure, the inner surface of which engages the pulp-suspension flow and the outer surface of which is exposed to the gas under pressure. Thus, the elastic wall structure changes its configuration or geometry due to pressure fluctuations in the pulp-suspension flow while the gas under pressure which acts through the elastic wall structure on the pulp suspension serves to damp the pressure fluctuations.

BACKGROUND OF THE INVENTION 
The present invention relates to paper machines. 
As is well known, in such machines the pulp suspension or pulp stock from 
which the paper is manufactured is delivered by a pipe system to a 
headbox, and the present invention is primarily concerned with apparatus 
for damping pressure fluctuations in the stock suspension which flows 
along the interior of the pipe system to the headbox. 
As is well known, the pulp suspension flowing in the pipe system to the 
headbox is exposed to pressure fluctuations, for a number of reasons, and 
these fluctuations if transmitted all the way to the lip slice of the 
headbox will result in lack of uniformity in the paper which is 
manufactured. The situation with respect to such pressure fluctuations is 
ideal when throughout the entire lip slice of the headbox there is a 
suspension flow in which the quantity of dry matter suspended is uniform 
while the velocity of flow is constant. If this flow is uniform over the 
entire width of the slice but varies with passage of time, then in the 
longitudinal direction of the paper machine there will be variations in 
the dry weight of the paper. 
If the pulp suspension flow is maintained constant with respect to time but 
is different at different locations along the width of the paper machine, 
then there will be a transverse variation of weight in the dry content of 
the paper. This type of variation is not damped by way of the present 
invention, nor by way of any other known damping systems acting at the 
pipe system which delivers the stock to the headbox, but transverse 
equalization can be taken care of by proper adjustment of the lip slice 
through suitable known spindles which are available for providing a fine 
adjustment of the depth of the lip slice across the width thereof. 
If the pulp stock flow, when measured simultaneously at the entire aperture 
of the lip slice, is independent with respect to time and in addition, at 
any point across the width of the paper machine, is on the average equal 
over a relatively long interval but different from one point of time to 
another point of time, then there will be produced in the paper, across 
the breadth of the machine, randomly situated heavier and lighter areas, 
or so-called residual variation. Such variations are caused first as a 
result of turbulence vortices produced in the headbox and acting on the 
output flow rate and secondly by a small-scale non-uniform distribution of 
the dry matter in the pulp suspension. 
This latter turbulence cannot be damped but is influenced by the particular 
design of the headbox. On the other hand, the small-scale dry matter 
distribution in the pulp suspension will indeed be equalized by way of the 
present invention in a manner which is superior to or at least equal in 
economy and efficiency to the best previously known designs. 
The variation in the dry weight of the paper longitudinally, in the 
direction of the machine, is primarily caused by variation in the flow 
rate which occurs in the stock input to the headbox by way of the pipe 
system. Secondly, such variations are caused by pressure waves which are 
always present in the pipe system while being propagated with the velocity 
of sound, the latter variations being converted at the aperture of the 
slice into variations in the kinetic energy of the jet. In the third place 
these variations are caused by large-scale consistency variations in the 
stock supply pipe. 
Thus, in summary, it is to be observed that the input fluctuation signals 
with respect to which the present invention is concerned are the dynamic 
pressure variations at the lip slice, while the output fluctuation signals 
are the variations in the hydrostatic pressure in the pipe system, 
variation of the pressure at the supply pump, variation in the pressure 
drop occurring in the flow, pressure pulses due to vibrations which are 
transmitted to the pipe system through the supports thereof, and pressure 
variations resulting from turbulence vortices particularly at valves, at 
bends in the pipe system, etc. 
It has been found in practice that the different pressure fluctuation 
signals each have their own characteristic frequency spectrum which often 
is fairly wide. However, the pressure fluctuation signals of pumps, for 
example, are characterized by clearly observable peaks at frequencies 
consistent with the speed of rotation of the pump and its multiples and 
subharmonics. 
Paper machine headboxes, as shown in the prior art, may be divided into 
three main groups, namely, (a) headboxes provided with an air cushion 
situated directly in the headbox, or so-called air cushion headboxes, (b) 
hydraulic headboxes provided with an air cushion separate from the headbox 
itself, wherein the air tanks are located either in the approach pipe 
system of the pulp suspension in advance of the distribution header or 
after the distribution header, and (c) hydraulic headboxes which have no 
air cushions at all. 
By utilizing air cushions in connection with the headbox, an attempt is 
made to equalize pressure variations occurring in the pulp suspension flow 
in advance of the lip slice, such pressure variations originating either 
in the stock system preceding the headbox or in the headbox itself. 
In the air cushion headbox according to group (a), the damping of the 
pressure variations, during the passage of time, is in most cases highly 
efficient because in these cases the surface area of the flowing stock 
which is in contact with the air cushion is comparatively large, while the 
depth of the stock flow, measured at right angles to the flow direction, 
is relatively small. Such headboxes also have the advantage that in them 
the air cushion usually extends up to a location which is quite close to 
the discharge lip or slice of the headbox, so that at the region between 
the location where the air cushion acts and the slice the possibility of 
generation of new pressure fluctuations is at a minimum. 
However, in spite of the above advantages of the group (a) type of 
headboxes, this type has in recent times been replaced in modern, fast 
paper machines by hydraulic or fully hydraulic headboxes as set forth 
above in groups (b) and (c). The reason for this is the easier 
accommodation of the latter types of headboxes in connection with the more 
modern twin-wire formers and on the other hand the lower manufacturing 
costs involved with groups (b) and (c). The greater turbulence of the 
stock jet discharging from the slice and the more favorable intensity 
distribution therein, together with the superior homogeneity of the stock 
resulting therefrom, have also promoted the use of these hydraulic 
headboxes. However, as against the above advantages thereof, hydraulic 
headboxes have displayed problems arising from the above pressure 
fluctuations. It has very often been necessary to provide a headbox 
originally intended to be fully hydraulic with one or more separate air 
tanks intended to replace the air cushion of an air cushion headbox. With 
respect to the location of these separate air tanks, various design 
solutions have been provided, and in some of them the air tanks have been 
connected to the pulp stock pipe system in advance of the headbox. In 
other known designs, the air tanks are situated above the headbox itself, 
being joined thereto by connecting pipes or by a connecting duct 
communicating with the upper part of the headbox. 
Constructions of this latter type, however, have the drawback that in the 
air tank above the headbox the depth of the free liquid over the central 
axis of the liquid stream is relatively large, or the communicating pipes 
from the headbox to the air tank must be dimensioned so as to be 
relatively narrow as compared with the cross section of the main flow 
passage. In both of these cases the damping characteristics are 
substantially impaired, as compared with the pressure variation damping 
capability of the standard air cushion headbox. 
SUMMARY OF THE INVENTION 
It is accordingly a primary object of the present invention to provide a 
construction according to which the pressure fluctuations as referred to 
above can be damped in a manner which is superior to previously known 
solutions, particularly with regard to efficiency and economy. 
Thus, it is one of the important objects of the present invention to 
provide an apparatus capable of effectively damping pressure fluctuations 
which occur in the pulp suspension flow in the pipe system which is 
situated in advance of the distribution header of the headbox. 
A further object of the present invention is to provide a 
pressure-fluctuation damping construction of simple design capable of 
being accommodated in various available spaces, even if the latter are 
relatively limited. 
In addition it is an object of the present invention to provide a damping 
apparatus which has the largest possible damping area so as to bring about 
in this way as efficient a damping of the pressure fluctuations as 
possible. 
Yet another object of the present invention is to provide a damping 
apparatus which damps pressure fluctuations while altering the cross 
section of the pulp suspension flow in such a way that the change in the 
cross section of flow will also act to damp pressure fluctuations. 
An additional object of the present invention is to provide a damping 
apparatus enabling the pulp suspension to be delivered to the headbox in a 
uniform manner and with minimum turbulence. 
The objects of the present invention also include the provision of an 
apparatus which will prevent air from being mixed in which the pulp 
suspension. In other words, it is an object of the present invention to 
provide an apparatus which will maintain the stock suspension closed off 
from air or other gas under pressure which is used for damping purposes. 
With known paper machines, the headboxes often are adjustable so that their 
position can be changed, and it is a still further object of the present 
invention to provide a highly effective connection of the damping 
structure into the system in such a way that the adjustment of the headbox 
can still be carried out effectively. 
In connection with this latter feature involving an adjustable headbox, the 
adjusting movement of which is accompanied by at least part of the pipe 
system which delivers the stock suspension to the headbox, it is already 
known to use elastic connecting structure which includes two comparatively 
long bellows which are joined by a relatively long intermediate tube. With 
this known type of elastic connecting structure there is at the location 
of the bellows a rigid inner pipe the diameter of which is somewhat 
smaller than the pipe which conveys the pulp suspension and which is 
assembled with the fixed intermediate pipe so that the latter pipes are 
situated partly one within the other. The drawback with this type of 
construction, especially when utilized in connection with the pulp stock 
supply of a headbox, is that there remains between an inner pipe and the 
bellows an annular space which is open to and communicates with the pulp 
stock pipe, so that the pulp stock can enter into this annular space. 
After a certain time, with this latter type of construction it is possible 
that the stock in the latter annular space forms clumps which become 
entrained into the pulp stock flow so that such clumps cause defects in 
the paper web. 
It is thus a further object of the present invention to provide a 
construction which will avoid these latter drawbacks while at the same 
time serving to provide an elastic connecting structure to be used with 
the damping apparatus while at the same time requiring only an exceedingly 
small space and providing for the stock a flow which is smoother than has 
heretofore been possible. 
In accordance with the invention the apparatus includes a pipe system for 
delivering the pulp suspension to a headbox with the suspension flowing 
along the interior of the pipe system. An enclosure means has a hollow 
interior for enclosing a gas such as air at a pressure greater than 
atmospheric pressure. The pipe system includes an elastic wall means 
having an inner surface which defines part of the interior of the pipe 
system for engaging pulp suspension flowing therethrough, this elastic 
wall means having an outer surface which is exposed in the hollow interior 
of the enclosure means to the gas under pressure therein. This elastic 
wall means will respond to an increase in the pressure of the suspension 
with respect to the pressure of the gas so as to increase the cross 
section of the suspension flow where the suspension engages the elastic 
wall means. Also the elastic wall means will respond to a decrease in the 
pressure of the suspension with respect to the gas pressure in the 
enclosure means for decreasing the cross section of flow of the suspension 
so that through the elastic wall means pressure fluctuations in the 
flowing pulp suspension will be damped. 
This elastic wall means includes, according to one embodiment of the 
invention, a tubular portion for surrounding the pulp-suspension flow and 
having an end fixed with a portion of the pipe system which is adjustably 
movable together with the headbox, the elastic wall means forming an 
extension of the latter portion of the pipe system. A flexible bellows 
means surrounds the elastic wall means at the region where it is connected 
to the above adjustable portion of the pipe system. This bellows means is 
fixed at one end together with the elastic wall means to the above portion 
of the pipe system and at an opposite end directly to the enclosure means. 
In this way an elastic connecting structure is provided for maintaining 
the damping of pressure fluctuations while at the same time providing for 
the possibility of adjustment of the headbox.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to FIG. 1, there is schematically illustrated therein an 
enclosure means 10a in the form of air tank made, for example, of steel 
and enclosing within itself an air space V in which a gas such as air 
under pressure greater than atmospheric pressure is accommodated. A pipe 
system which supplies the pulp stock suspension to the headbox includes 
the fragmentarily illustrated pipe 20 which delivers the pulp suspension 
in the direction of the arrow F shown at the left of FIG. 1 toward the 
enclosure means 10a and a pipe 21 which is fragmentarily illustrated and 
continues the flow of the pulp suspension in the direction of the arrow F 
shown at the right of FIG. 1 toward the headbox, these pipes 20 and 21 of 
the pipe system being respectively fixed to opposite ends of the enclosure 
means 10a as illustrated. 
In accordance with the invention the pipe system includes in the interior 
of the enclosure means 10a an elastic wall means which in the example of 
FIG. 1 takes the form of a tube 30a. This elastic wall means which takes 
the form of the tube 30a may be made, for example, of a fluid-impervious 
rubberized fabric. The tank or enclosure means 10a terminates at its 
opposed ends in a pair of endless wall portions 14, and the elastic tube 
or pipe 30a terminates at its opposed ends in a pair of outwardly directed 
flanges which engage the outer surfaces of the endless wall portions 14 of 
the tank 10a. The pipes 20 and 21 respectively terminate at their ends 
illustrated in FIG. 1 in outwardly directed flanges which engage the 
flanges at the end of the tube 30a, and suitable bolts or the like are 
used for connecting the flanges at the ends of the pipes 21 to the wall 
portions 14 of the tube 10a while compressing the flanges at the ends of 
the pipe 30a between the flanges at the ends of the pipes 20 and 21 and 
the end wall portions 14 of the tank 10a. In this way the tubular elastic 
wall means 30a is fluid-tightly connected with the pipes 20 and 21 while 
forming an extension thereof, providing for uninterrupted flow of 
suspension in the direction of the arrows F in FIG. 1 from the interior of 
the pipe 20 along the interior of the elastic tube 30a into the interior 
of the pipe 21, and at the same time in the interior of the enclosure 
means 10a it is possible for the elastic wall means 30a to expand and 
contract as described below in order to achieve the damping of pressure 
fluctuations in the flowing pulp suspension. The pulp suspension is 
delivered to the inlet end of the pipe 30a by the pipe 20 from a suitable 
pump while the outlet pipe 21 serves to participate in delivery of the 
pulp suspension to the headbox which is not illustrated. 
As is apparent from the cross-sectional schematic illustration in FIG. 2, 
it is possible for the tubular elastic wall means 30a to assume different 
cross-sectional configurations. Thus, the pressure of the gas within the 
enclosure means 10a will normally substantially equal the pressure of the 
suspension flowing through the tubular elastic means 30a. However, if the 
pressure of the flowing suspension increases with respect to the gas 
pressure then the tubular elastic wall means 30a can respond by 
automatically changing from the condition shown at 30a in FIG. 2 into the 
condition shown at 30a", whereas if the pressure of the suspension drops 
the elastic wall means can automatically change its geometry to assume the 
configuration 30a' indicated schematically in FIG. 2. 
It can be seen from the above that the tubular elastic wall means which 
defines the part of the pipe system which is located within the interior 
of the enclosure means changes its cross-sectional configuration to 
equalize the pressures of the gas within the enclosure means and of the 
suspension flowing through the tubular elastic means whereby pressure 
fluctuations in the flowing pipe suspension will be damped. It should be 
noted that the tubular wall means which in the present embodiment is 
constructed of a fluid-impervious rubberized fabric, will not necessarily 
stretch or compress since a rubberized fabric (or other reinforced rubber 
structure) will generally not be distensible to any significant extent. 
Rather the change in the cross-sectional configuration of the flow passage 
occurs by way of the tubular elastic wall changing its geometrical shape 
through flexure or oscillation of the rubberized fabric wall in the 
absence of stretching. 
In the illustrated example the enclosure means 10a carries in its interior 
a substantially rigid means for protecting and in this case supporting the 
elastic wall means 30a. In the illustrated example, this substantially 
rigid means includes a horizontal substantially flat wall 12 which extends 
across the interior of the enclosure means 10a and is situated directly 
beneath the tubular elastic wall means 30a for supporting the latter in 
the manner apparent from FIGS. 1 and 2. Thus the supporting wall 12 simply 
extends across the interior of the tank 10a and is supported at its 
opposite side edges at the inner surface of the tank 10a. This tank is 
itself carried by suitable supporting structure 11 situated, for example, 
on a floor. 
In the embodiment of FIG. 3, there is an enclosure means 10b which 
corresponds to the enclosure means 10a and operates in the same way while 
also being connected to the inlet pipe 20 and the output pipe 21 in the 
manner described above. This tank 10b of FIG. 3 is of a circular cross 
section and has in its interior a concentric elongated damping pipe 30b in 
the form of a tubular elastic wall means made, for example, of reinforced 
rubber and also having normally a circular cross section. The suspension 
flows horizontally as indicated by the arrows F. In this embodiment the 
tubular elastic wall means 30b is surrounded by a substantially rigid 
means 13 which serves to protect and support the elastic wall means 30b 
while at the same time permitting the latter to expand and contract or, in 
other words, oscillate radially outwardly and inwardly as best seen in 
FIG. 9. The details of the substantially rigid means 13 are set forth 
below in connection with FIG. 9. 
Referring now to FIG. 4, there is illustrated therein an embodiment of the 
invention where the pulp stock flows in a substantially vertical direction 
as indicated by the arrows F. The enclosure means 10c of this embodiment 
is in the form of a relatively low, vertical air tank. This air tank 10c 
terminates at its lower open end in an outwardly directed flange 14 which 
is fixed to a similar flange situated at the upper end of a lower supply 
pipe 20. This pipe 20 which receives the upwardly flowing suspension from 
the pump has at its upper end region an enlarged circular wall portion 15a 
which terminates in the upper end flange fixed to the flange at the bottom 
end of the tank 10c. Thus, this enlarged portion 15a of the pipe 20 may be 
considered as forming the bottom end of the tank 10c, although strictly 
considered this part 15a forms the upper portion of the pipe 20 inasmuch 
as the pulp suspension flows upwardly along the interior of the upper 
portion 15a of the pipe 20 while at the same time flowing in part radially 
outwardly from the smaller-diameter portion of the pipe 20 toward the 
outer wall of the tank 10c. 
The inner concave surface of the enlarged pipe portion 15a has fixed 
thereto the bottom ends of a plurality of vertical rods 16 which carry at 
their top ends a baffle 15 of substantially circular dish-shaped 
configuration having a lower concave surface directed toward the upper 
concave surface of the enlarged pipe portion 15a. The outer peripheral 
edge of the baffle means 15 is situated inwardly of the upper portion 15a 
of the pipe 20 so that the suspension flows upwardly around the outer edge 
of the baffle means 15 to the upper surface thereof. 
Situated above and spaced from the baffle means 15 is an annular elastic 
wall means 30c which has an outer peripheral portion clamped tightly 
between the flange 14 of the tank 10c and the flange at the upper end of 
the enlarged pipe portion 15a. This elastic wall means 30c thus has the 
configuration of an annular diaphragm, and it terminates in an inner 
circular peripheral portion which has a flange fixed to and engaging a 
flange 14 at the lower end of a pipe 17 situated in the interior of the 
tank 10c as illustrated. Below this flange 14 at the bottom end of the 
pipe 17 is a ring which surrounds the inner peripheral portion of the 
diaphragm and which is pulled tightly up toward the flange 14 at the 
bottom of the pipe 17 for fluid-tightly clamping a flange at the inner 
periphery of the diaphragm 30c to the bottom end of the pipe 17. This pipe 
is fixed at its top end to an upper circular wall portion of the tank 10c, 
so as to form in this way an extension of the outlet pipe 21. The circular 
pipe 17 is situated concentrically in the tank 10c. 
Thus, with this embodiment of the invention the pulp suspension will flow 
through the space which is defined between the baffle means 15 and the 
elastic wall means 30c in a substantially radial direction inwardly toward 
and then into the pipe 17. The elastic wall means 30c can expand and 
contract or, in other words, oscillate outwardly and inwardly between the 
solid line position thereof shown in FIG. 4 and the dot-dash line position 
30c'. Thus the elastic wall means 30c is free to oscillate and change its 
configuration as required in response to pressure variations and pressure 
pulses in the pulp suspension flow inasmuch as the outer or upper surface 
of the elastic wall means 30c is exposed to the air under pressure in the 
space V whereas the lower or inner surface of the elastic wall means 30c 
directly engages the flowing suspension. The particular embodiment shown 
in FIG. 4 is suitable for use in those situations where only a limited 
space, considered horizontally, is available for the structure of the 
invention. 
In the embodiment of the invention which is shown in FIG. 5, there is also 
an enclosure means 10d for containing in its hollow interior V a gas such 
as air under pressure, with the supply and outlet pipes 20 and 21 
extending horizontally while being connected to the opposed ends of the 
tank 10d in the manner shown schematically in FIG. 5. In this embodiment, 
the pipe system includes in the interior of the enclosure means 10d an 
elongated channel of U-shaped cross section having a substantially rigid 
bottom flat wall 19 and a pair of opposed upwardly directed side walls 18, 
as shown particularly in FIG. 6. Thus, this channel 18, 19, terminates in 
a pair of elongated upper side edges which are spaced from each other, and 
the elastic wall means 30d of this embodiment covers the channel 18, 19 
while extending between and being situated in engagement with the upper 
free side edges of the side walls 18. Thus, only the top wall of the 
portion of the pipe system within the enclosure means 10d includes the 
elastic wall means of the invention in the embodiment of FIGS. 5 and 6. 
The substantially flat elastic wall means 30d of this embodiment has 
opposed side flanges which are respectively fixed fluid-tightly to the 
opposed flanges which extend outwardly from the side walls 18 at the upper 
edges thereof. In addition, this elastic wall means 30d is formed 
integrally with upwardly extending transverse ribs which are respectively 
fixed to transverse substantially rigid upright plates 22 which at their 
opposed ends are fixed together with the side edges of the wall means 30d 
to the flanges at the upper ends of the side walls 18. Thus, the elements 
22 together with the ribs at the upper surface of the elastic wall means 
30d extend transversely with respect to the direction of flow and serve to 
support and protect the elastic wall means 30d. The channel 18, 19 is 
itself supported by substantially rigid support members 23 which are 
schematically illustrated and which are situated in the interior of the 
tank 10d at the lower region thereof as illustrated. 
In the embodiment of FIG. 7, the pipe system includes a curved supply or 
inlet pipe 20 and a curved outlet pipe 21. The upper end of pipe 20 and 
lower end of pipe 21 are are coaxial and fixed in the manner described 
above respectively to the lower and upper ends of a vertical enclosure 
means 10e which is supplied in its interior with a gas such as air under 
pressure. The pipe system of this embodiment includes in the interior of 
the enclosure means 10e the elongated elastic wall means 30e in the form 
of a pipe or tube the opposed ends of which are fluid-tightly connected in 
the manner described above to the inlet and outlet pipes 20 and 21. This 
vertical elastic-walled damping tube 30e is concentrically situated in the 
interior of the tank 10e and is surrounded by a substantially rigid means 
14e in the form of a perforated or open-spaced protective tubular 
supporting structure which enables the exterior surface of the tubular 
elastic wall means 30e to be exposed to the gas under pressure within the 
enclosure means 10 e. 
The details of the substantially rigid protecting means 14e are illustrated 
in FIG. 8 which the details of the substantially rigid protecting means 13 
of FIG. 3 are illustrated in FIG. 9. The substantially rigid means 13 and 
14e serve to protect the tubular elastic wall means of FIGS. 3 and 7 both 
against air pressure surge and pressure surge of the pulp suspension. 
Referring to FIGS. 7 and 8 it will be seen that the substantially rigid 
means 14e includes a plurality of vertically extending rods or bars 25 
which engage the outer surface of the elastic tube 30e while extending 
longitudinally thereof and being distributed circumferentially around the 
axis thereof. These vertical rods 25 are fixedly carried at their opposed 
end regions by horizontally extending rods 52 which are fixed at their 
inner ends to the rods 25 and at their outer ends to the inner surface of 
the tank 10e. Between these vertical rods 25 there are a plurality of 
arcuate bars 50 each of which is fixed at its opposed ends to the pair of 
rods 25 between which it extends, and these arcuate bars 50 are arranged 
in a series of circles longitudinally along the elastic pipe 30e in the 
manner apparent from FIGS. 7 and 8. Thus the vertical rods 25 and the 
arcuate bars 50 will define between themselves relatively large spaces in 
which the elastic wall means 30e can expand and contract or, in other 
words, radially oscillate outwardly and inwardly between the positions 
30e" and 30e' indicated in phantom lines in FIG. 8. 
According to the embodiment of FIGS. 3 and 9, the substantially rigid means 
13 includes a plurality of horizontally extending rods or bars 26 fixed to 
inner ends of radially extending rods 54 which at their outer ends are 
fixed to the inner surface of the tank 10b. These horizontally extending 
rods 26 are fixed to the adjoining ends of the arcuate bars 56 which are 
arranged in circles around the tubular elastic wall means 30b in the 
manner apparent from FIGS. 3 and 9. However, in this embodiment this 
tubular elastic wall means 30b is integrally formed at its outer surface 
with a plurality of radially extending fins 27 which extend longitudinally 
along the tubular elastic wall means 30b while projecting radially 
therefrom and being distributed circumferentially about the axis of the 
tubular wall means 30b. These fins 27 are clamped between the arcuate rods 
56 so that in this way the elastic wall means 30b is protected by the 
substantially rigid means 13 while at the same time being free to expand 
and contract or, in other words, radially oscillate outwardly and inwardly 
as is apparent from the phantom line illustration 30b' shown in FIG. 9. 
Thus, in each of the above-described embodiments, the tubular wall means 
will change its configuration by oscillating in response to the changes in 
pressure in the pulp suspension flow relative to the gas pressure in the 
associated enclosure means. The wall means, being formed of reinforced 
rubber, such as a rubberized fabric or equivalent, and therefore being 
substantially unstretchable, will expand and contract in the sense that it 
will change its geometrical configuration by flexing or oscillating to 
change the cross-sectional configuration of the flow passage defined 
thereby. 
In all of the above-described embodiments of the invention, the compressed 
air situated within any of the enclosure means referred to above is 
maintained at a pressure which of course is substantially equal to the 
pressure of the pulp suspension flowing through the pipe system along the 
inner surface of the elastic wall means whose outer surface is exposed to 
the air under pressure. The purpose of the elastic wall means of any of 
the above embodiments is to damp out pressure fluctuations in the form of 
pulses or oscillations occurring in the flowing pulp suspension, and at 
the same time the elastic wall means of the invention will prevent the air 
under pressure from having access to the flowing suspension. The pulses or 
oscillations are efficiently damped out only by the air cushion formed in 
the interior air space V but also by the changing cross section of flow 
resulting from the change in geometry of the elastic wall means. Thus, in 
the event that the pressure of the pulp suspension flowing in the 
direction of the arrows F increases, then the flow cross section of the 
pulp suspension will also increase with the result that the velocity of 
flow decreases, thus achieving an equalizing effect. On the other hand, if 
the pressure of the flowing pulp suspension decreases, then the cross 
section of flow thereof defined in part by the inner surface of the 
elastic wall means of the invention will correspondingly decrease, so that 
the velocity of flow will correspondingly increase to achieve also in this 
case an equalizing effect. Thus, by changing the configuration of the 
cross section of the flow passage through which the pulp suspension 
travels, by way of the damping means of the invention, and in addition 
because the elastic wall means of the invention, engaged at its exterior 
surface by the air under pressure, extends parallel to the direction of 
suspension flow, it becomes possible to introduce the pulp stock into the 
headbox in a condition free of turbulence and with the greatest possible 
uniformity. In addition, connections required for control devices and 
other accessory equipment are capable of being conveniently arranged with 
the structure of the invention. 
Referring now to FIGS. 10-14, the embodiments of the invention illustrated 
therein also include an enclosure means 110 in the form of a tank having 
an interior space V in which a gas such as air under pressure is situated. 
This tank 110 also is made, for example, of steel and communicates in any 
suitable way with a source of compressed air. Through the enclosure means 
110 there extends a damping tube made, for example, of a fabric in the 
form of a reinforced rubber sheet material. In the pipe system illustrated 
in FIG. 10, one end of the tubular elastic wall means which extends 
horizontally through the tank 110 is connected with the outlet pipe 122 by 
way of an elastic connecting means 130a of the invention. In the example 
shown in FIG. 10, the opposite end of the tubular elastic wall means in 
the interior of the tank 110 is connected through an elastic connecting 
means 130' with the adjoining end of the inlet or supply pipe 121 of the 
illustrated pipe system. This elastic connecting means 130' may be 
identical with the elastic connecting means 130a and serves primarily to 
render possible a proper longitudinal fitting or mounting of the inner 
elastic tubular wall means 113 in the interior of the tank 110 in a highly 
favorable manner. 
Referring to FIGS. 10 and 11, the pulp suspension flows in the direction of 
the arrows F shown in FIG. 11 and is supplied from a pump by way of the 
inlet pipe 120 into the tapered pipe 121 which terminates at its right 
end, as viewed in FIGS. 10 and 11, in a flange which while it can be 
connected directly to the tank 110 is instead connected as illustrated by 
way of the elastic connecting means 130' on the one hand to the tank 110 
and on the other hand to the inlet end of the tubular wall means 113 which 
is shown schematically in FIG. 11. After traveling through the elastic 
tubular wall means 113 the pulp stock reaches the tapered pipe 122 and 
flows from the latter into the distribution header 124 of the headbox. 
This header 124 is adjustable together with the pipe 122 when the headbox 
itself is adjusted. The elongated tubular elastic wall means 113 is 
protected within the tank 110 by way of a substantially rigid means made 
up of the longitudinally extending rods 114 and the circular rings 115 
which are connected to each other with the longitudinal elements 114 
engaging the exterior surface of the tube 113 so as to support and protect 
the latter while still permitting expansion and contraction thereof as 
described above. The longitudinal bars or rods 114 which directly engage 
the exterior surface of the tube 113 are distributed about the latter 
while extending longitudinally in the direction of flow, whereas the rings 
115 extend transversely to the direction of flow. Suitable supports 111 
are provided to support tank 110. 
Referring to FIGS. 11-13, it will be seen that in this embodiment the end 
of the tank 110 which is nearest to the headbox is connected with the 
flange 123 at the inlet end of the pipe 122 by way of a flexible bellows 
means. Thus the outwardly directed flange 123 at the inlet end of the pipe 
122 is fixed to a ring 116 which serves to clamp between the ring 116 and 
the flange 123 the outwardly directed flange 113a of the elastic tube 113. 
In addition, a ring 132a which surrounds the ring 116 is fixed by suitable 
bolts or the like to the flange 123 while clamping between the ring 132a 
and the flange 123 a sidewall of a flexible resilient convolution 130a of 
the bellows means which is illustrated in detail in FIG. 12. This bellows 
convolution 130a may be made, for example, of rubber, although other 
elastic material may also be used. The bellows convolution 130a forms one 
of a plurality of bellows convolutions which also include the convolutions 
130b and 130c, and all of these convolutions of the bellows means surround 
and are spaced from the end region of the elastic tube 113 which is joined 
to the flange 123 of the pipe 122. The several bellows convolutions while 
being endless are of the illustrated substantially U-shaped cross section, 
and their adjoining side walls are clamped between the rings 132b which 
are bolted together so as to have the positions illustrated in FIG. 12, 
these rings 132b also surrounding and being spaced from the elastic wall 
means 113. It will be noted particularly from FIG. 13 that the general 
configuration of the bellows convolutions and rings 132a, 132b corresponds 
to the general configuration of the cross section of the elastic wall 
means 113 which in the illustrated example is substantially elliptical. 
The bellows convolution 130c has a sidewall directly engaging a flange 112 
at the end of the tank 110 while a ring 132a serves to fluid-tightly fix 
the left side wall of the convolution 130c to the right end of the tank 
110, as viewed in FIG. 12. The number of rubber bellows convolutions may 
vary as desired, depending upon the magnitude of the displacements of the 
headbox and the pipe 122 connected thereto. As indicated by the arrows S 
in FIG. 12, the pipe 122 together with the headbox can be adjusted 
vertically, but it is also possible to provide for horizontal adjustment 
in a direction normal to the plane of FIG. 12. It is to be noted that the 
hollow interior of the tank 110 communicates with the interior of the 
bellows means illustrated in FIG. 12 so that the several elastic 
convolutions of the bellows means are filled at their interior with the 
air under pressure which is supplied to the interior space V of the tank 
110. 
FIG. 14 illustrates an embodiment of the invention where the bellows means 
has only a single convolution 130a. This single rubber bellows 130a of 
FIG. 14 is fixed at one of its side walls between the ring 132a and the 
flange 123. This ring 132a of course surrounds the ring 116 which serves 
to fix the end flange of the elastic tube 113 to the flange 123 of the 
pipe 122 in the manner shown in FIG. 14. A ring 112a serves to fix the 
left side wall of the bellows 130a of FIG. 14 to the end 112a of the tank. 
It will be noted that the rigid rings 132b which connect the bellows 
convolutions to each other in FIG. 12 serve to maintain these convolutions 
in a configuration consistent with the cross-sectional configuration of 
the elastic pipe 113. 
FIGS. 12 and 13 illustrate a limiting means for limiting the extent of 
adjustable movement. This limiting means includes a plurality of brackets 
133 which are fixed to the right end of the tank 110 and extend therefrom 
longitudinally in the direction of suspension flow. These brackets 133 of 
the limiting means fixedly carry at their outer ends vertical plates 150 
forming a slide plate means slidably engaging the surface 134 of the 
flange 123. Thus, the pressure within the tank and within the bellows 
means serves to urge the flange 123 of the pipe 122 against the slide 
plate means 150 fixedly carried by the limiting means 133, and thus the 
plate 123 can slide in a vertical plane at its surface 134 along the slide 
plate means 150 to provide for the adjusting movement while at the same 
time the extent of adjusting movement is limited by engagement of the 
outer edge of the flange 123 with the limiting brackets 133. 
Thus, with the above elastic connecting structure of FIGS. 10-14 it is 
possible for the pipe 122 which is rigidly fixed to the distribution 
header 124 of the headbox to move in a direction of the arrows S of FIG. 
12 and simultaneously in a horizontal direction perpendicular thereto. 
Similarly, minor torsion about the longitudinal axis of the tube 113 is 
possible. This possibility of adjustment is very favorably obtained by 
utilizing the above-described comparatively long elastic inner tube 113 of 
the damping apparatus of the invention as well as the elastic connecting 
means composed of the bellows means of the invention connected on the one 
hand to the flange 123 and on the other hand to the tank 110. 
Of course, the invention is not to be narrowly confined to the details 
described above and shown in the drawings by way of example only, inasmuch 
as the invention may vary within the inventive concept defined by the 
claims which follow below.