BACKGROUND ART In the latest generation of diesel engines the fuel quantity fed to the injectors always exceeds that required for engine operation. The excess fuel is therefore returned to the fuel tank via an overflow valve.

To optimize the space within the engine compartment, the overflow valves are associated with the fuel filter connected to the tank feed pump. In the known art the valves are either constructed as an integral part of the filter, or are fixed to a filter discharge conduit.

The periodic replacement of the filter, which is in one piece with the overflow valve, means that the valve is unnecessarily lost, while being in reality designed for a theoretical life equal to the life of the vehicle.

The object of the present invention is to overcome the said drawback within the framework of a simple and rational solution.

DISCLOSURE OF THE INVENTION The invention achieves said object by virtue of the characteristics defined in the claims.

Specifically, the invention provides a quick coupling device enabling an overflow valve to be removably associated with the exit conduit of a filter.

The device of the invention comprises retention means which are partly associated with the filter and partly associated with the valve, and comprise at least one movable element able to cooperate therewith to maintain the overflow valve associated with the filter.

In a preferred embodiment of the invention, the retention means associated with the filter comprise an annular portion branching from the surface of the filter as a prolongation of the discharge conduit, to receive the valve. Said portion presents, symmetrical about its axis, two slots in correspondence with which a shoulder is present on the valve, to define together with said slots a seat for receiving the movable element provided to maintain the valve associated with the filter.

The movable element preferably consists of a fork spring presenting two arcuate portions having a radius equal to the outer radius of the valve body.

Alternatively, according to the invention the movable element can also consist of a pin to be inserted into a matching seat, of which one portion is associated with that part of the retention means associated with the valve and the other portion with the retention means associated with the filter.

Again alternatively, the movable element can be a screw. In this case a threaded hole is present in said annular portion and in the outer casing of the valve.

In a variant of the invention, the retention means comprise matching threaded portions for screwing the valve to the filter.

The characteristics and the constructional merits of the invention will be apparent from the ensuing detailed description given with reference to the

figures of the accompanying drawings, which illustrate a preferred embodiment thereof given by way of non-limiting example.

Figure 1 is an exploded perspective view of the invention.

Figure 2 is the section II-II of Figure 1.

Figure 3 is a partial perspective view of the invention.

Figure 4 shows the section of Figure 2 with the valve associated with the filter.

Said figures show a filter 1 comprising an outer casing 10 provided with a fuel entry conduit 2 and two exit conduits 3 and 4. The exit conduit 3 is intended to be connected to the engine injectors, not shown as they are known. Instead the exit conduit 4 is intended to be connected to the engine tank, not shown, via an overflow valve 5 to be associated with the filter 1 by retention means 6.

With reference to Figure 3, said retention means 6 are partly associated with the filter 1 and partly with the valve 5. Specifically, the retention means 6 associated with the filter 1 comprise that portion 40 of the conduit 4 which emerges from the upper surface of the casing 10 and is intended to receive the lower portion of the valve 5. The portion 40 of the conduit 4 presents in proximity to its upper edge two diametrically opposing slots 41 the purpose of which will be apparent hereinafter. Instead, the retention means associated with the valve comprise an annular shoulder 50.

The slots 41 together with the annular shoulder 50 define a seat for receiving a movable element able to axially retain the valve inside the conduit portion 40. In the illustrated embodiment said movable element is in the form of a fork-shaped spring centrally presenting two identical

opposing arcuate portions 70 having a radius of curvature matching that of the annular shoulder 50 of the valve 5.

The valve 5 is provided lowerly with an O-ring 52 as a seal element against fuel seepage.

When the filter 1 is to be replaced the overflow valve 5 must be quickly removed. After disconnecting the connectors of the fuel entry conduit 2 and exit conduit 3, the overflow valve 5 is removed by extracting the fork- shaped spring to enable the valve 5 to be moved axially. In this manner the valve 5 can be extracted from the portion 40 of the conduit 4.

On mounting the new filter the valve 5 is inserted into the portion 40 of the conduit 4 (Figure 3), then the fork-shaped spring 7 is inserted into the slots 41 to prevent axial translation of the valve 5. The valve 5 is prevented from leaving the portion 50 by virtue of the engagement of the annular shoulder 50 against the spring 7, as can be seen in Figure 4.