The present invention first and foremost relates to a component of a rainwater drainage system in underpressure.

Rainwater drainage systems in underpressure are also caiied si.phonic roof drainage systems or UV-rainwater drainage systems, whereby OV stands for the Finnish Urnpi V ^' irtaus which means "closed flow".

In rainwater drainage systems, rainwater that fails on a roof, is led away via one or several openings in the roof or in a roof gutter to a drain pipe which is connected to a suitafa.1e drai ag system.

In conventional rainwater drainage systems, the rainwater is led away fay the drain pipe, in free fall as it were.

As illustrated in figure 1, there is also air suction, which hinders a rapid drainage of the rainwater in the drain pipes.

.In underpressure rainwater drainage systems, referred to as underpressure systems in short, the drainage of the rainwater through the drain pipe is additionally powered by the underpressure created when air suction at the top of the drain pipe is prevented. •Mr suction is prevented by applying so-called roof outlets on the roof on the level of the drain openings.

Via the rool outlets the rainwater is led to horizontal iy extending collector pipes which in turn end in a vertical down pipe.

As soon, as the whole down pipe is filled with rainwater and thus a vertical water column is formed, the drainage system is primed, or, in other words, we speak of a UV rainwater drainage system that is started.

In said situation the mass of the water column in the UV rainwater drainage system does indeed cause an underpressure, such that rainwater is sucked in and can be led away at high speeds.

This is illustrated by way of: example in figure 2. Ά big advantage of a rainwater drainage system in underpressure is that the dimensions of the drainpipes can- be kept smaller and less drainpipes and openings need to be made in the Iroof than with conventional rainwater drainage systems ,

In short, the drainage of rainwater can be done more efficiently with a UV rainwater drainage system.

A drawback of the known rainwater drainage systems in underpressure is that the supply pipes need to be made with various diameters. Ά criterion to realise a good flow in such UV rainwater drainage system, is indeed that in places where drainpipes come together the conditions i the arriving Liquid need to be the same,

However, it is generally known that the flow of a liquid in a pipe is linked with friction losses (also called load- losses} I whereby less friction loss occurs as a pipe with a greater diameter is applied.

In snort, it is necessary to ensure that rainwater which is led via a relatively long route to a certain point in the drainage system goes through pipes with a relatively big diameter, whereas rainwater that is led to that same point in the drainage system can pass via a relatively shorter route through pipes with a relatively smaller diameter, so that it arrives with the same energy.

The application of pipes with different diameters is illustrated in figures 3 and 4.

A major drawback of the known rainwater drainage systems in underpressure is therefore that the design and the calculation of the applicable diameters are complicated.

Another drawback of the known rainwater drainage systems in underpressure is that many different components with different dimensions and diameters are used, such that a large variety of products, such as pipes and connecting pieces, need to be produced and stocked. Moreover, the installation of such known rainwater drainag system in underpressure needs to foe precisely according to the design, which is clearly much more complicated than with the conventional rainwater drainage systems, whereby use is made of pipes the diameters of which are not so diverse,

Another drawback of the known rainwater drainage systems in underpressure is that it is very complicated or as good as impossible to adapt such a rainwater drainage system at a later stage by adding a roof outlet and accompanying pipe, for example to solve a discovered lack of drain capacity after the installation. The purpose of the present invention is therefore to pro-vide a solutio for one or several of the aforesaid or possible other disadvantages.

More specifically, a purpose of th invention is to provide a solution which strongly simplifies the design of a rainwater drainage system in underpressure, as well as the installation thereof.

Another purpose of the invention is to restrict the need of components of various dimensions for a rainwater drainage system in underpressure as much as possible.

Yet another purpose of the invention is a rainwater drainage system in underpressure which continues to drain rainwater at high speed in very varying circumstances and which after installation is still easily adaptable. It is also a purpose of the invention to provide a solution for rainwater drainage systems in underpressure which is maintenance friendly by ensuring that no or little maintenance is necessary or that components which do require such maintenance are easily accessible.

To this end, the invention relates to a component of a rainwater drainage system in underpressure, which is provided with control means to control the flow rate through a drainpipe of the rainwater drainage -system in underpressure, whereby the control means are such that that they allow the flow through the drainpipe concerned to be increasingly reduced as and. when an underpressure in the drainpipe concerned becomes greater and/or as and when the flow speed in the drainpipe increases and vice versa.

Such component according to the invention is very advantageous, as the component controls the flow rate in a drainpipe of the rainwater drainage system in underpressure, such that the rainwater drainage system starts faster or is primed sooner.

Generally speaking, in rainwater drainage systems in underpressure, which are equipped with components according to the invention, the connecting pipes of the UV roof outlets under atmospheric pressure or gravity flow can foe made with greater flow diameters, such that they are simpler to maintain, block less easily and ensure a faster start up or priming of the system.

This is because due to the greater diameters of the connecting pipes subject to gravity flow, the horizontal UV collector pipes fill up faster such that the down pipe can be primed faster,

In a preferred em odiment of a component according to the invention, the control m s allow the flow rate through the drainpipe concerned to be changed by making the dimensions of th flow-through opening of the drainpipe concerned o a supply thereto smaller or by changing the shape of this flow-through opening

Such embodiment of a component according to the invention has the ma or adva age that it is easy to re lise and this even in a self-ad usting way without unnecessarily complicated adjusters having to be provided, which is illustrated hereinafter in more detail.

In a possible embodiment of a component according to the invention, the control means comprise at least one movable or deformable control element which essentially is formed by at least one of the following elements:

- a movable flap;

- a movable sheet;

- a membrane;

- an elastic deformable element; or,

- a piston in cylinder.

Every one of said embodiments of a component according to the invention has its advantages _g whereby on the one hand _? for example in an embodiment with a movable flap or piston, the position of the control element and the accompanying flow rate in the drainpipe can be determined beforehand reasonably easily and correctly, which is not evident in an embodiment with an elastic membrane.

On. the other hand, an embodiment with an elastic membrane has the advantage that it is very maintenance friendly, because there are no mechanical components.

Another preferred aspect of a component according to the invention consists in that the control means are provided with at least one movable or deformabie control element which is intended to come into direct contact during operation with the drained away rainwater and whereby a movement or deformation of the control, element which determines the position thereof is the direct consequence of this contact with the drained away rainwater.

The major advantage of such embodiment of a component according to the invention is that it is effectively self- adjusting, whereby sections thereof increasingly reduce the flow rate in the drainpipe concerned because these sections take up another position in the drainpipe at an. increasing und rpressu and/or an increasing flow rate in the drainpipe or vice versa and this merely based on the contact of the component with the running rainwater.

Such embodiment of a component according to the invention also has the advantage that it is very maintenance friendly to manufacture, whereby no or hardly any maintenance is necessar .

In a very preferred embodiment of a component according to the invention said control element is essentially formed by a deformable or elastic membrane that covers and .hermetically seals n opening or cavity in a wall section, whereby a contact side of the membrane during operation is intended to come into contact with the drained away rainwater and the other side of the membrane is in contact with a medium present in a hollow, closed space which is delimited by the membrane and said wall section.

Such embodiment of. a component according to the inven ion. is very efficient as it can be easily installed in a rainwater drainage system in underpressure and thereafter automatically controls the flow rate in the drainpip concerned without additional means. The membrane hereby automatically deforms under the effect of the prevalent underpressure in the drainpipe and preferably the design is such that the level of deformation corresponds with the desired reduction or increase of the flow rate in the drainpipe as the case may be.

In a special embodiment which will be clarified based, on the figures, the component is additionally provided with adjustment means with which the initial condition and the level of deformation of the membrane during operation can be ad usted.

Moreover, it is clear that such embodiment of a component according to the invention with membrane barely requires any or no maintenance.

In yet anothe embodiment of a component according to the invention, control engineering techniques can be applied, whereby electronic, mechanical or hydraulic, components can be used for the composition of the control means.

In such embodiment of a component according to the invention, the control means can, for example, comprise one or several of the following elements:

- a measuring instrument to measure the flow rate through a drainpipe or a roof outlet of the rainwater drainage system in underpressure concerned;

- a measuring instrument to measure the underpressure in a drainpipe or a roof outlet of the rainwater drainage system in underpressure concerned;

- an electronic control unit to manage the control means as a function of measurements made with a measuring instrument i a dr inpipe or a roof ou let of t e rainwater drainage system in underpressure concerned; and/or,

- an actuator to change the flow-through opening of a drainpipe of the rainwater drainage system in underpressure concerned or of the flow-through opening of a aapply thereof.

Such embodiment of a component according to the invention is of course more complicated, hut it allows solutions to be offered with more known techniques or in applications where with simpler means alone it appears not possible.

The invention also relates to a pipe piece that constitutes a component of a rainwater drainage system in underpressure according to the invention, as already described above.

The special characteristic of such pipe piece according to the invention is that it has a pipe wall in which a channel _? opening o cavity is provided which on the inside of the pipe piece is hermetically covered by a membrane to form said control means and whereby a wall section connects to the channel or opening or whereby wall section forms the cavity such that this wall section, together with the membrane, encloses a hollow, closed space.

Such embodiment of a pipe piece according to the invention of course has the advantag that it can be easily installed without additional elements during the installation of a rainwater drainage system in underpressure and can immediately fulfil its function as flow rate controlling component of the system. Moreover, the invention relates to a roof outlet which forms a component according to the invention of a rainwater drainage system in underpressure.

The special characteristic: of such roof outlet is that the roof outlet contains an ai shutoff valve i the form of a cover whereby, to form a hollow, closed space, centrally in the cover, a hollow, seaiahl.e tube is provided which extends perpendicular to the cover, whereby in the tube wall one or several passages are provided, whereby over the hollow tube a balloon- shaped membrane is applied which its the edges is hermetically connected with the outside of the tube wall, whereby the membrane covers said passage or passages and whereby by creating a underpressure outside the membrane in relatio to the pressure in the hollow closed space, the balloon-shaped membrane can blow up to increase the volume of the hollow space. The major advantage of such roof outle according to the invention is that the roof outlet can control the flow rate of a drainpipe connected to the roof outlet of a rainwater drainage system in underpressure by increasing or decreasing the volume of the hollow space and thus decrease and increase respectively the dimensions of the flow- through opening .

Such roof outlet according to the invention is also very easily accessible on the roof, for example for inspection or maintenance and the like.

Another major advantage of the application of the aforementioned -embodiments of a component according to the invention is that pipes can be used with the sarae diameter,, as the control means automatically adapt the dimensions of the low-through opening to the desired dimension in which flow in underpressure takes place. Consequently, it is much easier to design a rainwater drainage system in underpressure with such components according to the invention and the installation thereof is equally simple and can be done .by any subcontractor w o is also able to install a conventional rainwater drainage system.

.Another advantage of the application of components according to the invention resulting from this, is that only a limited number of types of such components and types of other components are needed to be able to realise any installation . That also implies an enormous cost reduction.

With the intention of be ter showing the cha acte istics of the invention, hereinafter, toy way of an example- without any limiting nature, a number of preferred embodiments are- described of a component of a rainwater drainage system, in underpressure according to the invention, as well as a pipe piece and a roof outlet according to the invention constituting such component, with reference to the accompanying draw gs, wherein: figures 1 and 2 respectively illustrate the operation of a conventional rainwater drainage system and a rainwater drainage system in underpressure;

figure 3 shows a perspective view of a section of a known rainwater drainage system in underpressure;

figure 4 shows a perspective view on a larger scale and with additional sections according to arrow 4 in figure 3;

figure 5 in cross-section shows a first embodiment of a component according to the invention, more specifically in an embodiment as a pipe piece according to th invention;

figures 6 to 11 in cross-section in a similar way show other embodiments of such component according to the invention which is made as a pipe piece according to the invention;

figures 12 and 13 in cross-section again illustrate a component according to the invention, which is made as a pipe piece according to the invention, in a first position and a second position respectively,' figures 14 and 1.5 show a perspective view and with representation of invisible sec ions in dotted line, of a component according to the inherition, which is made as a pips piece according to the invention, in a first and a second position respectively;

figures 16 and 1? a e c oss- sections, according to the planes indicated with the arrows F16 in figure 14 and the arrows F17 in figure 15 respecti ely;

figures 18 and 19 are cross-sections, according to the planes indicated with the arrows FIB in figure 16 and the arrows F19 in figure 17 respectively; and,

figure 20 in cross-section shows component accoraing to the invention that is made as a roof outlet according to the invention.

Figure 1 shows a section of a conventional rainwater drainage system 1, whereby in a roof 2 an opening 3 is provided to which a drainpipe 4 is connected. The rainwater 5 falls in free fall as it were through the drainpipe 4 whereby there is air 6 suction, which is disadvantageous for an efficient drainage of the rainwater 5, Figure 2 shows a section of a rainwater drainage system in underpressure 7 thereby this time on the level of the opening 3 in the roof 2, a UV roof outlet or a roof outlet with air shutoff vaive 8 has been installed which avoids the suction of air 6 via the drainpipe 4.

In case of sufficient rainfall, a vertical column of rainwater 9 is formed in the drainpipe 4 and the rainwater drainage system in underpressure 7 is started, whereby the mass of the vertical column of rainwater 9 strongly stimulates the drainage of the rainwater 5. An underpressure is created in the drainpip 4, more specifically a pressure that is lower in the drainpipe 4 than the atmospheric pressure in the surroundings, and the rainwater 5 is therefore drained at much higher speeds than in a conventional rainwater drainage system 1.

Figures 3 and 4 schematically illustrate a more realistic set-up of a rainwater drainage system in underpressure 1.

Several UV roof outlets 8 are connected hereby via a connecting pipe 10 to one or several horizontally extending collector pipes 11 which drai the rainwater 5 to one or several vertically extending down pipes 12.

A illustrated in figure , a UV roof outlet 8 can also be directly connected to a down pipe 12.

To ensure that the same pressure loss occurs in every route that the rainwater 5 can follow to a particular point in the rainwater drainag system in underpressure 7, the connecting pipes 10, as well as the different collector pipes 11, the down pipe 12. and separat sections thereof, need to be made with very varied diameters Dl to D6, as do the different collector pipes 11. It is clear that such rainwater drainage system in underpressure 7 requires a precise design, that many different components with very varied dimensions need to be sed, that the installation is very difficult and can easily result in mistakes, and the like.

A solution is offered to these problems with a component 13 according to the invention which is intended for application in such rainwater drainage system in underpressure .

A first possible embodiment of such component 1.3 according to the invention is shown in figure 5.

Such component 13 according to the invention is special, because it is provided with control means 14 to control the flow rate through a drainpipe 4 of the rainwater drainage system in underpressure 7.

The control means 14 are such that they allow the flow rate through the drainpipe concerned 4 to be increasingly reduced as and when an underpressure ΔΡ in relation to the atmospheric pressure Q in the drainpipe concerned 4 becomes greater or as the flow speed in the drainpipe 4 increases and vi e versa.

For the sake of clarity, underpressure ΔΡ refers to the pressure difference between the atmospheric pressure Q and the pressure P in the drainpipe 4 (ΔΡ ~ Q-P) .

In the example of figure 5 the component 13 itself comprises a section 15 of a drainpipe 4 of the rainwater drainage system in underpressure 7 in which the control means 14 are integrated. Indeed, the component 13 is made as a pipe piece 16 with which a drainpipe A of the rainwater drainage system in underpressure ? can be composed., The pipe piece 16 has a cylind ical wall 17 with diameter A, whereby centrally in the pipe piece 16 a wider part 18 is provided, formed by a wail section 19 with a diameter B which is greate than diameter A. Moreover, the control means 14 contain a control element 20 that is movable and deformafole and in the example shown is essentiall formed by a deformable or elastic membrane 21 that covers a cavity 22, formed by the wall section 19 of the wider part 181

The membrane 21 can, for .example, be made of a rubber or any synthetic material that has elastic properties.

The membrane 21 is connected with the cylindrical wail 17 on the edges 23 of the cavity 22 and hermetically seals the cavity 22, in a non-load,, non-de ormed condition, the membrane 21 can be cylindrical, which corresponds with the case whereby the wider part 18 extends over 360", i.e. around the whole contour of the pipe piece 16.

In other embodiments, the wider part 18 can only extend over a fraction of the contour of the pipe piece 16 and the membrane 21 in the non-load, non-deformed condition, has the form of a fraction of a cylinder. Obviously, according to the invention, pipe pieces 16 and wider parts 18 with completely different shapes and cross- sections can be applied and with membranes 21 adapted to these shapes.

A contact side 24 of the membrane 18 is intended to come into direct contact with the drained away rainwater 5 in the pipe piece 16 during operation, The other side 25 of the membrane 18 is in contact with a medium 26 that is present in the cavity 22, more specifically in a hollow, closed space 27 which is delimited by the membrane 21 and the wail section 20. Preferably this medium 26 is a gas, but it can also foe a liquid or solid material or a combination of all this and. the medium 26 can be put under pressure in the cavity 22 and the like. When in the pipe piece 16 there is a pressure ? that is equal to the atmospheric pressure Q (i.e. whe there is so underpressure Δ.Ρ) , the membrane 21 and the medium 26 in the closed, hollow space 27 are preferably adjusted thus that it extends in the extension of the cylindrical ¾?ail 17,

Thus, the membrane 21 in this condition in no way whatsoever forms any additional obstruction for the flow of rainwater 5 through the pipe piece 16. Furthermore, the control means 14 are such that they allow the flow rate through the drainpipe concerned 4 to be changed by altering the dimensions of the flow-through opening 28 of th drainpipe concerned 4.

More specifically in this case, with an increasing underpressure ΔΡ, in other words when the pressure P in the pipe piece 16 drops in relation to the atmospheric pressure 0, the membrane 21 will deform and mov in the direction indicated by the arrows R toward the centre of the pipe piece 16.

Accordingly^, the flow-through opening 28 of the pipe piece 16 is decreased, such that the flow rate through the pipe piece 16 drops too. When the underpressure &? drops again, the opposite occurs.

The position or shape of the membrane 21 is immediately determined by the size of the underpressure ΔΡ without, intervention of additional means.

It is clear that with such component 13 according to the invention, an automatic control of the flow rate through the pipe piece 16 is obtained, which allows a rainwater drainage system in underpressure 7 to be effectively kept in underpressure as well, as was put forward in the introduction.

Moreover, it is trivial that the component 13 is very simple to manufacture, ca be installed without any problem and hardly requires any or no maintenance. In the embodiment of figure 5, said wail section 19 which delimits the cavity 26 is at least partially part of the cylindrical wail 17 of the pipe piece 16 which is intended to be part of a drainpipe 4 of the rainwater drainage system in underpressure ? concerned.

Figure 6 shows another embodiment of a component 13 according to the invention which shows many similarities with the embodiment of figure 5,

However, in this case the membrane 21 is applied over an opening 29 in the cylindrical wall 17 whereby the side 25 of this membrane is in contact with a medium 26 in a hollow, closed space 27 <

This hollow closed space 27 is somewhat different, as it is delimited by the membrane 21 and by a wail section 30 that forms a control vessel 31 and is connected via a channel 32 to the opening 29.

To be able to adjust the condition in the hollow, closed space 27, adjustment means 33 are preferably provided according to the invention, In the embodiment of figure 6 these adjustment means 33 comprise a sealable cover 34 that provides access to the hollow, closed space 2 ^' ? in the control vessel 31 for adding or removing medium 26. The intention here is to be able to change the quantity of gaseous medium 35 and/or liquid or solid medium 36 in order to adjust the initial condition in the hollow, closed space 21, more specifically when an atmospheric pressure Q is prevalent on the contact side 24 of the mens rane 21.

Figure 7 shows another embodiment of a com onent according to the invention which also contains a section 15 of a drainpipe 4 and which more specifically is made again as a pipe piece 16.

However, in this embodiment the control element 20 of the control means 14 is essentially formed by a piston 37 which is movable backward and forward in a cylindrical tube piece 38 which extends laterally on the cylindrical wall 17 of the pipe piece 16. The head 39 or a section near the head 39 of the piston 37 is intended to come into contact with the drained away rainwater 5 during operation,

Furthermore;, o e piston 37 is powered by a spring 38 applied in the cylindrical lateral tube piece 39.

With an increase of the underpressure ΔΡ or therefore a drop of the pressure P in the pipe piece 16 the piston 37 moves in an outward direction out of the cylindrical tube piece 39, indicated wit the arrow S.

The head 0 of the piston 37 in this way makes the flow- through opening 28 in the pipe piece 16 smaller, such that in this embodiment the flow rate through the pipe piece 16 decreases as well. In the event of a drop of the underpressure &J? _f exactly the opposite occurs.

It is clear that such embodiment has essentially the same operation as the: previous embodiments of a component 13 according to the invention.

In figure 8 a similar embodiment of a component 13 according to the invention is shown, whereby this time the cylindrical tube piece 39 in which the piston 3? can move backward, and forward extends perpendicular to the wail 17 of the pipe piece 16 and not at an angle as is the case in figure 7. This oesn' t result in any essential changes in the operation of the component 13.

Figure 9 shows another embodiment of a component 13 according to the invention which is practically identical to the embodiment of figure 6,

In this figure 9 the component 13 is still made as a pipe piece 16, whereby this time this pipe piece 16 is intended to be placed vertically, whereas a pipe piece according to an embodiment shown in. figure 6 is suitable for a horizontal installation,

As can be deducted from, the figures, this change .requires another orientation of the control vessel 31 and the seal-able cover 34 thereof in relation to the direction in which the pipe piece 16 extends. A pipe piece 16 according to the embodiment of figure 9 has the advantage that it can foe installed in a vertical section of a drainpipe 4 that connects with an opening in the roof 2 close to the roof outlet 8, whereas a pipe piece 16 as shown in figure 6 is suitable for installation in horizontal section of a drainpipe 4, such as for example in a horizontal section of a connecting pipe 10 further away from the opening 3 in the roof 2. ftn advantage of an installation close to the roof 2 is that the component 13 is more easily accessible and thus makes any inspection and maintenance, as well as adjusting the adjustment means 33, simpler. Figure 10 builds on this idea and the membrane 21 of the control means 1,4 is installed even closer to the opening 3 in the roof 2, whereby it no longer extends centrally or symmetrically over the opening 2.9 towards the hollow space 27 in the control vessel 31, which was the case in the previous embodiment of figure 9.

More specifically in this case the membrane 21 extends to nea the edges 41 at the opening 3 in the roof 2, where the membrane 21 is attached to a section of the rainwater drainage system in underpressure 7 which forms a roof duct 42 or roof outlet 8.

To make this possible, the component according to the invention 13 must thus also comprise a section of a roof duct 41 or a roof outlet 8 in which the control means 14, in this case the membrane 21, are also integrated. In the embodiment of figure 11 a further integration of the control xs ans 14 in the roof outlet 8 or roof duct 41 has been realised, whereby in this case the control vessel 31 is integrated in an air shutoff valve 43 of the roof outlet 8 which forms a kind of cover provided at some distance E above the roof 2 in order to avoid the supply of air 6 to the drainpipe 4.

The wall section 30 which also delimits the hollow, closed space 2? is partially part of this air shutoff valve 43.

Another section of the wail section 30 which encloses the hollow space 2? constitutes the channel 32 to the control vessel 31.

The opening 29 in the drainpipe 4 or the pipe piece 16, and which is covered by the membrane 21, is provided at a distance F under the roof 2 in the pipe piece 16 or the drainpipe 4, just, as in the preceding cases of the figures 9 and 10,

In this embodiment of figure 11 the channel. 32 extends from this opening 29 into the air shutoff valve 43, more specifically through the bottom 44 thereof to above th level G of a liquid medium 36 which is possibly present in the control vessel 31.

In this case both a. pipe piece 16 and a section of a roof duct 42 or roof outlet S are part of the component 13 according to the invention. It is clear that adjusting the condition in the hollow, closed space 27 in this embodiment is even easier than with the preceding embodiments, as the cover 34 of the control vessel 31 is a cover 34 of the air shutoff valve 43 which is accessible from the roof 2 without any problem.

Figures 12 and 13 show yet another embodiment of a component according to the invention 13, whereby this time the control means 14 do not control the flow rate through a drainpipe 4 as a function of the underpressure ΔΡ, but whereby the control means 14 are directly controlled by the flow speed or the flow rate of the rainwater 5 through the drainpipe 4. In the shown example, the component 13 is again made as a pipe piece 16 whereby the control means 14 are formed by a piston 3 which can move backward and forward in a cylindrical tube piece 8, just as in the examples of figures ? and 8.

The piston 37 is hereby provided with a channel 45 for drained away rainwater 5 to flow through during operation.

The lateral position of the piston 37 in the cylindrical tube piece 38 and/or the shape of the channel 45 are hereby determined during operation by the flow-through speed of the drained away rainwater 5 through this channel 45 in the piston 37. Figure 12 s ows a first position of the piston 37 and shape of the channel 45 at. atmospheric pressure, whereby th piston 3 ^' 7 is partially retracted. Figure 13 shows a position whereby the piston 37 has moved more to the flow-through opening 28 according to the arrow S.

This embodimext of the figures 12 and 13 has a number of drawbacks and is therefore not a preferred solution, but the example indicates that the control means 14 cannot only be controlled toy an underpressure, but also by the flow- through speed of rainwater 5 through the component 13, even when there is no underpressure yet.

That is possible because the control means 14 have a certain shape, whereby more specifically the control means 14 are formed by the channel 45 in the piston 37 which has a curved shape or wav shape which forms an obstruction in the flow-through opening 28.

A drawback of this embodiment in relation to the preceding embodiments is that in rest mode, i.e. the absence of an underpressure in the component 13, there is already an obstruction with accompanying narrowing in the flow-through opening 28, formed by a section of the piston 37 and the channel 45. in this rest mode the rainwater 5 can flow through the wave-shaped or curved channel 45 in the piston 37, indicated by arrow U, and along the piston 37 according to a straightforward route indicated with arrow V, he obstruction foriued by the wave-shaped channel 45 in the piston 37 can in this condition ensure by its curved or waving design that tunning, falling water, fre failing under atmospheric pressure can already develop a reaction force on the piston 37, such that it can already start moving according to the arrow S and make the flow-through opening 28 even narrower, and this still before the component according to the invention 13 is in underpressu .

A movement of the piston 3 in the direction of the arrow S reaches its m ximum when the piston 37 is extended against the cylindrical wall 17 opposite the tube piece 39.

Prom that oment the flow-through opening 28 is narrowed to the opening forraed by the wave-shaped channel 45 and there is no further narrowing of the flow-through opening 28 with greater underpressures ,

Figures 14 to 19 show an alternative embodiment which shows similarities with the embodiments with membrane 21 of the figures 5 and 6.

In this case the opening 29 on the wail section 30 covered by the membrane is a rectangular opening 46. Such rectangular shape of the opening 29 has the advantage that a flat membrane 21 can easily be stretched over it, whereby it is guaranteed that the membrane 21 remains tight during operation . In this embodiment the wall section 30 is formed by a beam- shaped insert 7 which is partly sunk into the cylindrical wall 17 of the pipe piece 16, The rectangular opening 46 is provided in the beam-shaped insert 4? toward the inside 48 of the pipe piece 16. The membrane 21 covers this rectangular opening 46 and extends further over the edges 49 of the rectangular opening 46 up to the cylindrical wail 1? of the pipe piece .16. On the level of this cylindrical wail 17, th mem rane is connected, with this cylindrical wall 17 of the pipe piece 16, in order to achieve a smooth transition between the cylindrical wall 17 of the pipe piece 17 and the edges 49 of the rectangular opening 46 in the insert 47.

Thus, a smooth flow through the pipe piece 16 is ensured, despite the beam shape of the insert 47 sunk into the cylindrical wail 17.

Figures 14, 16 and 18 show the condition of the membrane 21 whe there is no underpressure &P in the pipe piece 16..

In this condition the membrane 21 is fiat and it extends in the plane 50 of the rectangular opening 46. As is shown, in the figures 15, 17 and 19, the membrane 2.1 deforms when, the underpressure ΔΡ increases into a spherical surface 51 in the direction of the arrow T toward the inside 48 of the pipe piece 16. The result is that the flow-through opening 28 gets ssaller and the flow rate through the pipe piece 16 is reduced. In the event of a drop of the underpressure ΔΡ, exactly the opposite oce rs ,

And finally, based on figure 2.0 another possible embodiment is discussed here of a component 13 according to the invention which this time is made entirely as a roof outlet 8, or even taote- precisely as an air shutoff valve 43 of such roof outlet 8, of a rainwater drainage system in underpressure 7.

The air shutoff valve 3 is made as a cover 52 whereby, to form a hollo*? _/ closed space 27, centrally in the cover 52, a hollow, seaiafole tube 53 is pro ided which extends perpendicular to the cover 52»

Several passages 55 are provided in the tube wail 54 of the hollow, sealable tube 53.

Furthermore, over the hollow tube 53 a balloon-shaped membrane 56 is applied which at its edges 57 is hermetically connected with the Outside 58 of the tube wall. 54.

The balloon-shaped membrane 56 covers said passages 55 and by creating an underpressure Δ.Ρ on the contact side 24 of the membrane 56 in relation to the pressure 0 in the hollow, closed space 27, the balloon-shaped membrane 56 can blow u to increase the volume of the hollow space 27. Increase and decrease of this underpressure ΔΡ result in an increase and decrease respectively of the volume taken up by the balloon-shaped membrane 56. The intention is that the ba1loo:n-shaped membrane 56 with the hollow tube 53 extends under the cover 52 into the opening 3 of the roof 2 and thus into the section concerned of the drainpipe 4.

Accordingly, the volume taken up by the balloon- shaped membrane 56 determines the dimensions of the flow-through opening 28 of the drainpipe 4 and thus the extent to which rainwater 5 can flow through this drainpipe 4,

The component 13 according to the embodiment of figure 20 is also provided with adjustment means 33 with which the conditio in. the closed, hollow space 27 can be adjusted.

In this case these adjustment means 33 are ade as a. movable section 59 with which the volume of the hollow, closed space 27 can be changed. To this end the hollow tube 53 extends through the cover 52 of the roof outlet 8, whereby the hollow tube S3 at the free end 60 that extends above the top 61 of the air shutoff valve 43 is provided with a seaiable cover 62. In this cas the movable section 59 is a plug 63 which is provided in the hollow tube 53 and via the positioning means 64 is movable up and down in th hollow tube 53 to a desired position. In this case these positioning means 64 are formed by a threaded rod 65 and screws 66 and 67, with which the plug S3 can be positioned in a certain position on the threaded rod 65.

The plug 63 is also provided with sealing means 68 with which the plug 63 can foe put in a sealed and non-sealed condition.

Mor specifically the plug 63 with the sealing means 68 can be put in a sealing condition whereby the plug 63 on the level of said desired position completely, hermetically seals the passage n the hollow tube 53.

Reversely, the plug 63 with the sealing means 68 can be put in a non-sealing condition whereby the plug 63 is loose in the hollow tube 53 to allow the plug 63 to be moved to another position with the positioning means 64.

In this case, the plug 63 is made as a rubber element 69 which is mounted over the threaded rod 65 and which on either side is provided with a screw 67 and a washer 70 to form the se ling means 68, whereby by screwing the screws 67 toward each other the rubber element 69 expands and the plug 63 is thus put in a sealing condition. The present invention is by no means limited to the embodiments described as an example of component 13 according to the invention of a rainwater drainage system in underpressure 7, as well as of a pipe piece 16 and; a roof outlet 8 according to the invention which form such a component 13, but such components 13, such pipe pieces 16 and such roof outlets 8 can be made in ail kinds of other forms and dimensions without departing from the scope of the invention .