The invention concerns a device at roof drains for dis¬ charging through the roof drain water being collected on the roof by means of a number of gullies whereby the water is discharged to a drainage pipe, which is common to the gullies, and whereby each gully has an inlet opening the upper edge of which is placed in the plane of the roof and also an outlet opening which is smaller than said inlet opening and is connected to said drainage pipe, and whereby a plate means is arranged in the gully under the plane of the upper edge of the inlet opening, which plate means has an area which blocks the water and is concentricly placed in relation to the outlet opening and has a larger projec¬ tion area than the area of the outlet opening, whereby is ensured that when the flow to the gully is of the dimen- sioned amount air is not sucked down into the gully and through the outlet opening due to the formation of a whirl.

A device of this kind is known from for instance Swedish patent 327 805. The device according to this patent oper¬ ates satisfactory when the gully is used with its own drainage pipe and ensures that a whirl can not be formed, which whirl sucks air through the gully when the flow of rain water is of the dimensioned amount. However, this device has deficiencies when it is arranged on a roof to¬ gether with a number of gullies and has a joint drainage pipe with all the gullies for discharging the rain water. For proper operation it is of importance that all of the gullies simultaneously have a "full flow" that is to say there is an unbroken water column, possibly with some air, in all the gullies in order to ensure that all the gullies operate satisfactory at the same time. It is also of impor-

tance that the pressure drop is maintained in all the gul¬ lies and that for instance one of the gullies does not show a complete air column due to lack of water or intermixing of air in the water. The object of the invention is to eli- inate these drawbacks which the known device has.

Usually the gutters on a roof construction have been con¬ nected together and the gutters have had no sloopness or a minimal of sloopness. A balancing of the amount of water between the different gullies on the roof was hereby achie¬ ved and the composition of the gullies was optimized in order to give an opi al capacity. There are now a demand that the operation shall be satisfactory also when the roof sloop is minimum and in spite of that maximum roof area shall apply to each gully. This means that the capacity of the gullies is of less interest and that the balancing of the flows of the system can not be reached by means of the gutters but must take place by balancing the different re¬ sistance of the system. It should therefore be logical to give the gully a greater influence on the operation of the drainage system by increasing the pressure drop over the gully. This will simplify the balancing of the piping and at the same time it is possible to increase the water speed which will give a better selfcleaning of the gully itself. The pressure drop of the gully compared with the available total pressure drop will be small anyhow.

Even if the gullies are designed for "full flow" it is a fact that this situation rarely occurs, which means that the system must be dimensioned hydraulicly not only for the dimensioned flow but also to give optimal properties con¬ cerning balancing, selfcleaning and sound also at small

flows and also when the amount of rain water to the indivi¬ dual gullies is unequal in comparison with what has been presumed when the system was designed for "full flow". At small rates of flow, also "full flow" gullies mix in air because it is the piping and not the gullies which decide the flows as far as "full flows" is concerned. The known gullies effect intermixing of air by that the water level in the gully is unstable whereby air will be drawn into the system as pulses of different size. This shall not be con- fused with that a whirl is formed in the center of the gul¬ ly, which whirl conducts air to the center of the gully and through its outlet. The known gullies were thus hydraulicly dimensioned for the rainwater drainage system and were ba¬ sed on that the water flows in the system were balanced and the flows being closed uniform water flows. However it has been shown that this is an uncomplete view for several reasons. In the first place the authorities state the di¬ mensioning amount of rainwater contrary to the demand for a coefficient of fullness which makes it possible to achieve selfcleaning of the system. This results in that the pipes are oversized for being self-cleaned. Secondly one must take into account when designing the system and its compo¬ nents that water has a density which is one thousand times higher than that of air. The pressure drop is the same for air and water but the speed of the air is about thirty ti¬ mes higher than that of water. Having this knowledge, the object of the invention is to prevent pulsations at other rate of flows than the dimensioning flow and to ensure that when the rainwater flow is normal, all gullies in the same system are operating with a suitable mixture of air in the water so that a continous water column exists from all the gullies to the outlet pipes of the system.

In order to eliminate the drawbacks of known designs and meet the theory stated above, the invention has the charac¬ terizing features stated in the following claims.

Two preferred embodiments of the invention will be descri¬ bed in the following with reference to enclosed drawings.

Fig. 1 is thereby a schematic cross-section of a gully ac¬ cording to a first embodiment.

Fig. 2 is a schematic view from above of the gully accor¬ ding to fig. 1.

Fig. 3 is a schematic cross-section of a second embodiment of the invention.

Fig. 4 is a schematic plan view of the gully according to fig. 3.

Fig. 1 shows a gully 1 which in a suitable way is placed in a gutter of a roof and the plane in which the gully is pla¬ ced, has the numeral 2. The inlet opening of the gully is surrounded by an edge 3 in flush with the roof plane 2 and is formed with a countersink so that a through-shaped re- cess is formed. The gully 1 has an outlet opening 5, which is directly connected to a drainage pipe 6, which is con¬ nected to an outlet pipe (not shown) being common to all of the gullies on the roof.

A plate formed means or disk 7 is arranged in the gully 1 as known per se, which disk has a blocking central area 8, which is larger than the outlet opening 5 in its projection

plane but thus smaller than the inlet opening of the gully. The disk 7 is placed a small distance under the edge 3 of the inlet opening. In this design the plate formed means 7 is in the form of a cap which is placed in the gully having a downwardly extended surrounding flange 9. A number of slots 10 (see fig. 2) , are formed in the outer area of the upper side of the disk 7, through which slots 10 the water flows down to the through- formed space 4 and further out through the outlet opening 5 of the gully. The blocking area 8 prevents, as known per se, that a whirl can be formed in the gully and that this whirl is drawn down into the outlet opening 5 thereby for¬ ming a column of air through the gully and the outlet ope¬ ning 5.

A cylindrical strainer 11 is placed on the top of the gully 9 and above the roof plane 2. The strainer is in the form of a cap and has a number of slots 12 for water flow into the gully. Normally water is allowed to be stored on the roof when it is raining, which means that there is a layer of water on the roof and the thickness of this layer may be about 50 mm. At dimensioning amount of flow the water layer on the roof is between

0 mm and 50 mm but normally the layer has a thickness which corresponds to that the gully is filled with water up to the edge 3. At dimensioning flow, water flows through the gully under so-called "full flow condition" which means that there is an unbroken column of water through the gully and the complete line of pipes.

The problem which is to be solved and which has been dis¬ cussed above is that when it flows less water through the

gully than the dimensioning flow, the pressure drop through the gully and the drainage pipe may disappear because the column of water is broken and hereby air will be drawn through the gully and through the line of pipes. This will disturb the system of gullies in that pulsations will occur and the velocity of the water flow will decrease. In order to ensure that there is an unbroken column of water when the water flow is smal¬ ler than the dimensioning water flow, small quantities of air is supplied to the outlet opening of the gully so that a mix¬ ture of air and water flows through the outlet opening. This mixture of air and water is created according to the invention by means of a flow pipe 13. The flow pipe 13 ex- tends airtight through the space between a plate formed means 7 and the outlet opening 5 and has an opening 14 pla¬ ced in the outlet opening 5 or just under the opening. The inlet of the pipe 13 is placed above the inlet opening 3 of the gully. The pipe 13 has a straight form through the cen- ter of the gully and through the blocking area 8 and above this area there is a straight part towards the inside of the strainer 11. Therefrom the pipe is bent to a tube bend 16, which extends with a small pitch along the inner side of the strainer and ends in about the middle of the strai- ner. A number of holes 17 are formed along the tube bend 16 and these holes form inlet openings for air to the flow pipe 13. The total area of the holes 17 corresponds to the cross-section area of the pipe 13.

When the water level on the roof 2 is under the end of the tube bend 16 over the roof, air will be drawn into the ho¬ les 17 and the air is passed down through the pipe 13 and

out of its opening 14 where the air is mixed with the wa¬ ter, which flows through the gully. The air will therefore be supplied in appropriate proportions during the complete flow process and pulsations in the system is hereby avoi- ded. When operating a certain embodiment of the invention, the maximum flow was about 3.2 1 per second. Air was mixed with the water and the flow could be decreased to 1 1 per second before some small pulsations could be noted. It has been shown that the smaller the pressure drop is in the p p® 13, the more stable flow is achieved but at the same time a certain part of available pressure for the system is lost, which means somewhat higher water level on the roof.

Figs. 3 and fig. 4 show a second embodiment of the inven¬ tion. The same numerals are used as for the former embodi¬ ment for the corresponding parts. The difference between this embodiment and the former embodiment is that according to fig. 3, the pipe 13 extends from the outlet opening 5 along the bottom of the gully towards its inner side and from here it is extended vertically in a straight part 18 which ends in a tube bend 16 similar to the tube bend shown in fig. 1. The pipe 13 is closed all the way through the space 4 as described in connection with the embodiment ac- cording to fig. 1. The advantage with this embodiment is that the problem of tightening the pipe when passing through the blocking area 8 is avoided.

The invention thus makes it possible to mix air in the wa- ter in the bottom of the gully in a controlled way and when the water level on the roof is lower than the level corre¬ sponding to the dimensioning flow above the plate formed

means 8.

It should be noted that the extension length of the flow pipe 13 and its form can be varied otherwise than what is shown. It should further be noted that the expression "area blocking against air" relates to the action of this area when the flow is at the dimensioning amount.