PRIOR ART Various types of drain plug are known in the field of components for sanitary installations, and in particular for hydraulic drain fittings.

The drain plug is mounted on a mouth end of the drain fitting and comprises a closure element which is operated by a pop-up lever which hence opens and closes the drain for example of a wash-basin, a bidet or a bathtub. These closure plugs are generally of plastic, metal or metal and plastic.

The drain fitting is also provided with a safety device known as an overflow which prevents water delivered by a left-open tap from spilling over while the plug-like closure element is closed. In practice, the overflow comprises, in an upper region of the wash-basin, bidet or bathtub, a hole dimensioned according to the volume of the wash-basin, bidet or bathtub and connected by a pipe to the drain fitting or, more often, directly to the plug of the drain fitting.

It will be apparent that the overflow safety device is costly both because of the hole provided through the ceramic part of the wash-basin, bidet or bathtub, and because of the independent pipe connecting the hole to the drain fitting: this involves a certain constructional complexity and a

lengthening of the production cycle. Even if the overflow safety device is applied after being separately prefabricated in plastic, it still represents an additional cost.

DISCLOSURE OF THE INVENTION An object of the present invention is therefore to obviate the aforestated drawbacks by providing an automatic safety drain plug for a drain fitting which enables a safety device of substantially reduced cost to be used.

Another object of the present invention is to provide an automatic safety drain plug for a drain fitting which is particularly reliable, simple and functional.

These and further objects according to the present invention are attained by an automatic safety drain plug for a drain fitting as defined in claim 1.

Further characteristics are defined in the subsequent claims.

BRIEF DESCRIPTION OF THE DRAWINGS The characteristics and the advantages of an automatic safety drain plug for a drain fitting according to the present invention will be more apparent from the ensuing description given by way of non-limiting example with reference to the accompanying schematic drawings, in which: Figure 1 is an isometric view from above of an automatic safety drain plug for a drain fitting, according to the present invention; Figure 2 is a sectional side elevation of the drain plug of Figure 1, inserted into a mouth of a drain fitting.

BEST MODE FOR CARRYING OUT THE INVENTION

The figures show a drain plug, indicated overall by 10, for a drain fitting 12.

In the illustrated example, according to the present invention, the drain plug 10 comprises a closure element 14 and a rod 16 connected to a pop- up lever (not shown in the figure), in accordance with the known art.

The plug-like closure element 14 is provided with an element 18 slidable, substantially in an axial direction, within a guide 20 provided below the closure element 14.

The drain plug 10 comprises opening means 22, maintained in a closed configuration until a pressure above the closure plug 10 reaches a predefined value. In the figures, between the slidable element 18 and a portion of the closure element 14, for example below the closure element 14, opening means 22 are provided in the form of lifting means, such as an elastic element maintained in a compressed configuration by engagement means 23 which are automatically released when the slidable element 18 reaches a predefined position.

In the example illustrated in the figures, the slidable element 18 and the guide 20 are axial, the slidable element 18 being provided with a circular head 24, for example of spherical cap form, and with a cylindrical stem 26.

The plug-like closure element 14 upperly presents a cylindrical recess 28.

The cylindrical guide 20, through which the stem 26 slides, is provided centrally on the base of said recess 28, the circular head 24 being slidable within the recess 28. A flexible diaphragm 30 is mounted on the recess 28 after inserting the stem 26 into the guide 20.

The stem 26 is connected lowerly to the rod 16 by a deformable annular structure 34. The stem 26 is inserted into the top of said connection

element 32 until it reaches a position in which it is locked within the annular structure 34. The connection element 32 is connected lowerly to the rod 16, for example by means of mutual screw threads.

Before fitting the connection element 32 to the stem 26 already mounted on the plug-like closure element 14, a helical spring acting as the elastic element 22 is mounted on the stem 26, followed by an annular plate 36, which is free to slide on the stem 26.

The engagement means 23 are provided below the closure element 14, they comprising a plurality of bars 38 (in the figures these being three in number and equally spaced apart), which extend in an axial direction and are provided lowerly with a step 40 re-entering substantially towards the axis, to retain the annular plate 36.

In this respect, the length of the bars 38 is such that the helical spring 22 is completely compressed and pushes against the annular plate 36.

The length of the bars 38 is also such that the annular plate 36 bears against the annular structure 34 of the connection element 32.

More precisely, the annular plate 36 has larger outer dimensions than the annular structure 34, which rests against an inclined inner surface 42 of the bars 38; this inclined inner surface 42 lies below the step 40 and is downwardly inclined inwards.

The operation and the more specific characteristics of the drain plug for a drain fitting of the invention are clear from the aforegoing description with reference to the figures, and are briefly as follows.

The closure plug 10 is located at the mouth of the drain fitting 12, hence generally in a hole provided in the ceramic with which wash-basins, bidets or bathtubs are constructed.

The bars 38 of the plug-like closure element 14 lock the spring 22 in a compressed position.

The pressure exerted by the overlying water column acts on the flexible diaphragm positioned externally on the top of the closure element 14 of the closure plug 10.

This pressure thrusts the diaphragm 30 downwards, to press against the circular head 24 of the slidable element 18. The stem 26 descends and sinks into the connection element 32. The penetration of the stem 26 causes lowering of the annular structure 34.

The annular structure 34 pushes against the inclined surfaces 42 of the bars 38, causing the bars 38 to flex outwards until the annular plate 36 is disengaged from the steps 40. At this point the spring 22 acts to thrust the closure element 14 upwards, so opening the mouth of the drain fitting 12.

The annular plate 36 is released from the bars 38 when a predefined pressure (corresponding to the rating of the drain plug 10) is reached.

The spring 22 is reloaded to a force exceeding the total weight of the maximum water column and those portions of the drain plug 10 which are forced upwards.

The closure element 14 of the drain plug 10 then rises from its seat, for example conical, in the drain fitting 12 on which it rests, to free the passage for water outflow.

To reset the drain plug 10, the diaphragm 30 is pushed until the slidable element 18 is returned to its initial locked position on the connection element 32.

Alternatively, the diaphragm 30 could be covered by a circular metal

element (in the form of a further plug). This metal element could have a 2/3 mm hole leaving the diaphragm uncovered. Instead of having the entire diaphragm in contact with the water, it is only this small portion which senses the overlying water column and releases the entire mechanism, a described.

Hence in practice, the drain plug according to the invention monitors the rise in water level in the wash-basin (or bidet or bathtub) closed by a plug- like closure element, until a certain predefined level is attained. On reaching this level, the spring of the drain plug is released so that the closure element of the drain plug rises to allow water outflow through the normal drain of the wash-basin (or bidet or bathtub).

As an alternative to the elastic element, the lifting means 22 can use an electric motor or mechanism, a compressed air or gas mechanism or a chemical phenomenon to raise the closure element 14 of the drain plug 10.

It should be noted that the closure element 14 of the drain plug 10 of the invention can alternatively be provided, as opening means 22, with a valve with an elastic element which collapses at a certain pressure above the drain plug 10; when the pressure returns below a predefined pressure, the valve returns to its original position by virtue for example of an underlying spring (in this case, water outflow takes place on a diameter less than the original outflow diameter of the drain fitting 12).

The rod 16 of the drain plug 10 is generally connected to a pop-up lever of traditional type.

The characteristics of the automatic safety drain plug for a drain fitting according to the present invention are clear from the aforegoing

description, as are the relative advantages, which include: - simple and reliable use; - the bathtub (or bidet or wash-basin) which uses this drain plug does not require an overflow safety device of known type ; - casting a bathtub (or bidet or wash-basin) in ceramic without the overflow safety device is simpler and less costly ; - saving the cost of the overflow safety device fitted to bathtubs (or bidets or wash-basins), which in the known art is of materials such as plastic, metal or other materials; - the drain plug of the invention can be mounted on a traditional bathtub (with existing overflow safety device), to ensure maximum safety for example if a cloth or other obstacle should obstruct the water evacuation hole ; - aesthetic and effective cleaning (no residues or mould) in the region containing the hole of the overflow safety device; - facility for considerable personalization of the drain plug, which can include identification of the concern which uses the plug.

Finally it is apparent that the automatic safety drain plug for a drain fitting conceived in this manner is susceptible to numerous modifications and variants, all falling within the scope of the invention; moreover all details can be replaced by technically equivalent elements. In practice the materials used and the forms and dimensions can be chosen at will according to technical requirements.

The scope of protection of the invention is therefore defined by the accompanying claims.