Field of application of the invention

The present invention finds application in the field of direct-operated check valves. More precisely, the present invention relates to check valves the plug of which is moved by a first-class lever.

Review of the background art

The check valves operated by a first-class lever are widely used in various fields of the art. Among the most widespread uses of the valves of this type there is the reversible obstruction of a delivery duct to adjust the introduction of a liquid (for example, water) into a tank. In this particular use, the inlet opening of the valve is connected to the outlet opening of the duct so that the pressure of the liquid in the duct tends to remove the plug from the seat thereof, opening the valve. The lever moving the plug is connected to a floater, the position of which in the tank depends on the filling level of the latter. The Archimedes' thrust undergone by the floater due to the liquid possibly present in the tank tends to close the valve, opposing the liquid pressure in the delivery duct. When the tank is full, the floater orientates the lever so that it presses the plug against the seat thereof, so that the valve is closed. When the tank is emptied, the aforesaid Archimedes' thrust is lost and the lever, due to the pressure applied on the plug by the liquid in the delivery duct, rotates about the fulcrum removing the plug from the seat thereof and, consequently, opening the valve. As specified above, in these valves it is the floater, by means of the lever, which presses the plug against the seat thereof when the tank is full. This, however, is a disadvantage since, in the event of detachment of the floater from the lever, the valve opens regardless of the filling level of the tank. Since the check valves of the aforesaid type are prevalently installed in the flushing tanks of toilets, the detachment of the floater from the lever may give rise to considerable problems. To overcome this drawback, the Applicant has conceived a new type of check valve, the operation of which is the reverse of that described above. More pre cisely, in the check valves of this second type (object of the Italian patent appli- cation for a utility model No. ME2014U000004 corresponding, in the new for mat, to No. 202014902237198) the inlet opening of the valve can be connected to the outlet opening of a delivery duct so that the plug is pressed against the seat thereof by the pressure of the liquid in the duct, i.e., so that the pressure of the liquid in the duct tends to close the valve. The lever and the floater have, overall, a weight such that the weight force acting thereon, in the absence of the

Archimedes' thrust on the floater, overcomes the pressure applied on the plug by the liquid in the delivery duct, opening the valve. When the tank is full, the floater is supported by the Archimedes' thrust and the pressure of the liquid in the delivery duct keeps the valve closed. When the tank is emptied, as the Ar- chimedes' thrust on the floater is removed, the weight of the lever and of the floater causes the lever to rotate about the fulcrum, removing the plug from the seat thereof and, consequently, opening the valve.

In this second type of valve, since the liquid present in the delivery duct presses the plug against the seat thereof, if the floater becomes detached from the lev- er, the valve remains advantageously closed.

A valve should be considered according to one of the two types shown above, connected to a delivery duct which introduces a liquid inside a tank. Starting from a configuration in which the tank is full and the valve is closed, if the tank starts to empty, the valve opens due to the pressure of the liquid contained in the delivery duct or due to the weight of the floater. This can be an issue if the tank is to be emptied for a certain volume of liquid before the filling process thereof starts. Object of the invention

It is the object of the present invention to overcome the aforesaid drawbacks by indicating a check valve operated by a lever connected to two floaters, adapted to open only when the filling level of the tank, during an emptying thereof, has reached a determined lower limit.

Incidentally, the term "filling level" of the tank means the level of the free surface of the liquid inside the tank.

Summary of the Invention

It is the object of the present invention a direct-operated check valve which can be connected to a delivery duct to adjust the introduction of a liquid, under pres sure in said duct, into a tank,

said valve comprising a body including:

• an inlet opening at which said body is connectable to said duct (i.e., the outlet opening of the latter);

• an outlet opening;

• a connection chamber between said inlet and outlet openings,

said chamber communicating:

- with said inlet opening at a first connection path, and

- with said outlet opening at a second connection path;

• a plug housed in said chamber and movable between:

- a first opening position, at which said plug does not obstruct any of said connection paths, so that a liquid can flow from said inlet opening into said outlet opening crossing said chamber, and

- a second closing position, at which said plug sealingly obstructs said sec ond connection path,

said inlet opening being connectable to said duct so that, when said plug is in said closing position, an overpressure at said inlet opening with respect to said outlet opening applies a force to said plug tending to keep said plug in said closing position;

• means for moving said plug between said opening and closing positions, said moving means comprising:

- a lever, preferably of the first-class type, having a fulcrum at said body, said lever being in contact with said plug;

- a first element suitable for floating, at least partially, at the free surface of said liquid (due to the Archimedes' thrust) when said first element is at least partially immersed in said liquid. Said first element suitable for float ing will be identified in the following of the present description with the term "first floater".

Said first floater being integrally connected to said lever so that, when said first floater is at least partially immersed in said liquid so as to undergo an Archimedes’ thrust, said Archimedes’ thrust generates a first torque on said lever by means of said first floater, tending to rotate said lever so as to move, or allow the movement of, said plug from said opening position to said closing position,

in which, in accordance with the invention, said moving means further comprise:

- a second element suitable for floating, at least partially, at the free surface of said liquid (due to the Archimedes' thrust) when said second element is at least partially immersed in said liquid. Said second element suitable for floating will be identified in the following of the present description with the term "second floater";

- a cord connected to said lever at a first end, and to said second floater at a second end opposite to said first end. As an alternative to the cord, it is possible to use another flexible element extended in length (such as, for example, a chain) suitable for connecting the lever and the second floater to each other. Here and in the following of the present description, the word "cord" means any flexible element extended in length of the afore said type.

Said cord being connected to said lever and to said second floater so that, when said cord is tensioned due to the weight force acting on said second floater, possibly reduced by the Archimedes’ thrust undergone by said second floater when the latter is at least partially immersed in said liquid, said tension generates a second torque on said lever, tending to rotate said lever so as to move said plug from said closing position to said open ing position, said first floater and said lever having, as a whole, a weight such that:

• when:

- said plug is in said closing position,

- said inlet opening is connected to said duct with an overpressure at said inlet opening with respect to said outlet opening, and

- said cord is not tensioned,

the weight force acting on said lever and on said first floater generates a third torque on said lever:

- tending to rotate said lever so as to move said plug from said closing posi- tion to said opening position,

but

- not being sufficiently strong to rotate said lever so as to move said plug from said closing position to said opening position,

so that said plug remains in said closing position due to the force applied thereto by said overpressure,

and

• when:

- said plug is in said opening position,

- said inlet opening is connected to said duct with an overpressure at said inlet opening with respect to said outlet opening, and

- said cord is not tensioned,

the weight force acting on said lever and on said first floater generates a fourth torque on said lever

- tending to keep said plug in said opening position,

and

- being sufficiently strong to keep said plug in said opening position, thus overcoming the force applied thereto by said overpressure,

said second floater being ballasted so that, when:

• said plug is in said closing position,

· said inlet opening is connected to said duct with an overpressure at said inlet opening with respect to said outlet opening, • said cord is tensioned, and

• said tension on said cord reaches a limit value which is equal to or lower than the tension due only to the weight force acting on said second floater, said second torque, together with said third torque, is sufficiently strong to rotate said lever so as to move said plug from said closing position to said opening position, thus overcoming the force applied to said plug by said overpressure. Incidentally, the first floater is shaped so that, when it is at least partially im mersed in said liquid so as to undergo an Archimedes' thrust, said Archimedes' thrust is greater than the weight force acting on said lever and on said first floater. Similarly, the second floater is shaped so that, when it is at least partially immersed in said liquid so as to undergo an Archimedes' thrust, said Archime des' thrust is greater than the weight force acting on said second floater. Con versely, the first and the second floater would not qualify as "floaters".

When the valve of the invention is connected to a delivery duct which introduc es a liquid inside a tank, the valve is adapted to open only when the filling level of the tank, during an emptying thereof, has reached a determined lower limit.

To understand this, a configuration should be considered in which the valve is closed and the tank is full, i.e., the filling level of the tank is such that both float ers are at least partially immersed in the liquid, floating therein at the free sur face.

By starting a tank emptying process (for example, by removing a plug that seal- ingly obstructs an opening at the bottom of the tank), the filling level of the tank gradually decreases. Due to this, the level of the second floater lowers together with the lowering of the free surface of the liquid in the tank, while the first float er emerges from the liquid and is kept suspended by the lever. What has been said is a consequence of the fact that, as specified above, when the plug is in the closing position and the cord of the second floater is not tensioned, the weight force acting on the lever and on the first floater generates on the lever a torque which is not sufficiently strong to open the valve. The latter remains closed as long as the cord of the second floater is not tensioned. More precise ly, when the filling level of the tank decreases to the point of making the second floater emerge from the liquid, the weight force acting on the second floater generates on the lever a torque sufficiently strong to open the valve. Following the opening of the valve, new liquid comes out from the delivery duct to which the valve is connected, entering the tank.

Supposing now that the emptying of the tank is interrupted (for example, by ob- structing said opening with said plug), the tank begins to fill up. Due to this, the level of the second floater rises, together with the raising of the free surface of the liquid in the tank. Even if the cord ceases to be tensioned as a result of the raising of the second floater, the valve remains open since, as specified above, when the plug is in the opening position and the cord of the second floater is not tensioned, the weight force acting on the lever and on the first floater generates on the lever a torque sufficiently strong to keep the valve open. When the liquid in the tank reaches the first floater, the latter rises making the lever rotate and closing the valve (i.e., ceasing to oppose the overpressure at the inlet opening of the valve with respect to the outlet opening).

The fact that the valve of the invention is adapted to open only when the filling level of the tank, during an emptying thereof, has reached a determined lower limit, reduces the number of times the valve must be opened and reclosed and ensures a more effective exchange of the liquid. The advantages are therefore evident, both in terms of wear of the mechanical components, and in terms of quality of the liquid in the event that the latter is, for example, water.

Incidentally, when the valve is closed, the weight force acting on the lever and on the first floater generates on the lever a torque which is not sufficiently strong to open the valve, whereas, when the valve is open, the weight force acting on the lever and on the first floater generates on the lever a torque sufficiently strong to keep the valve open. To avoid any doubt, this is a consequence of the fact that the overpressure at the inlet opening of the valve with respect to the outlet opening when the valve is closed is clearly higher with respect to when the valve is open. In other words, the force applied on the plug by the liquid pre sent in the delivery duct when the valve is closed is much stronger with respect to when the valve is open.

Other innovative features of the present invention are shown in the following description and are referred to in the dependent claims. According to an aspect of the invention, said lever is a first-class lever, said first and second floaters being connected to said lever at a first arm there of;

said plug being shaped so that, when said inlet opening is connected to said duct with an overpressure at said inlet opening with respect to said outlet open ing, said overpressure applies a force to said plug tending to press said plug against a second arm of said lever opposite to said first arm,

said valve comprising means for centering said plug, with respect to said sec ond connection path, upon a movement thereof from the opening position to the closing position.

Advantageously, the centering means ensure that the plug is correctly posi tioned with respect to the second connection path, upon a movement thereof from the opening position to the closing position. In other words, the centering means ensure that the plug is positioned so as to sealingly obstruct the second connection path upon a movement thereof from the opening position to the clos ing position.

According to another aspect of the invention, said centering means comprise:

• a seat, made in said body, at least partially delimited by a substantially cylin drical wall,

said seat being crossed by said second connection path;

• a substantially discoidal element integrally connected to said plug and shaped so as to correspond to said substantially cylindrical wall,

said substantially discoidal element being at least partially housable in said seat so as to correspond to said substantially cylindrical wall,

said seat being positioned so that an at least partial housing of said substantial ly discoidal element in said seat, so as to correspond to said substantially cylin drical wall, defines the arrangement of said plug in said closing position (so as to sealingly obstruct said second connection path).

According to another aspect of the invention, alternative to the preceding one, said centering means comprise:

• a seat, made in said body, at least partially delimited by a substantially cylin drical wall, said seat being crossed by said second connection path;

• a substantially frustoconical element integrally connected to said plug at the long base thereof, and shaped so as to correspond to said substantially cy lindrical wall at least at the long base thereof,

said substantially frustoconical element being at least partially housable in said seat so as to correspond to said substantially cylindrical wall at least at the long base thereof,

said seat being positioned so that an at least partial housing of said substantial ly frustoconical element in said seat, so as to correspond to said substantially cylindrical wall at least at the long base thereof, defines an arrangement of said plug in said closing position (so as to sealingly obstruct said second connection path).

Brief description of the Figures

Further objects and advantages of the present invention will become apparent from the following detailed description of an embodiment thereof and from the accompanying drawings, merely given by way of explanation and not by way of limitation, in which:

- Figure 1 shows, in a diagrammatic and partial cross section, a check valve according to the present invention, connected to a delivery duct to adjust the introduction of a liquid, under pressure in said duct, into a tank. In figure 1 the tank is full and said valve is shown in a configuration in which it is closed;

- Figure 2 shows, in a diagrammatic and partial cross section, the valve of Figure 1 closed during the emptying of the aforesaid tank;

- Figure 3 shows, in a diagrammatic and partial cross section, the valve of Figure 1 closed during the emptying of the aforesaid tank, in an instant, fol lowing that of Figure 2, in which the filling level of the tank is such as to make the opening of the valve of Figure 1 imminent;

- Figure 4 shows, in a diagrammatic and partial cross section, the valve of Figure 1 in a configuration in which it is open;

- Figure 5 shows, in a diagrammatic and partial cross section, a variant of the valve of Figure 1 in a configuration in which it is closed.

Detailed description of some preferred embodiments of the invention In the following of the present description, a Figure may also be shown with ref erence to elements not expressly indicated in that Figure but in other Figures. The scale and the proportions of the various elements depicted do not neces sarily correspond to the real ones.

Figure 1 shows a check valve 1 , object of the invention, connected to a delivery duct 2 which leads into a tank 3 at an outlet opening 4 thereof. The duct 2 is preferably cylindrical, at least in the section thereof inside the tank 3, with the longitudinal axis arranged vertically. The opening 4 is preferably placed near an upper wall 5 of the tank 3. A liquid 6, under pressure in the duct 2, can be intro- duced into the tank 3 through the opening 4. The valve 1 is connected to the duct 2 at the opening 4 to adjust the introduction of liquid 6 into the tank 3.

The valve 1 comprises a body 10 including an inlet opening 1 1 , an outlet open ing 12 and a chamber 13 interposed between the openings 1 1 and 12 to create a connection therebetween. More precisely, the chamber 13 communicates with the opening 11 at a first connection path 14, and communicates with the open ing 12 at a second connection path 15. The openings 1 1 and 12, as well as the chamber 13 and the connection paths 14 and 15 are preferably cylindrical and more preferably coaxial, with the longitudinal axis thereof arranged vertically. Even more preferably, the openings 1 1 and 12 have a cross section with an in- ner diameter smaller than that of the inner section of the chamber 13, but great er than that of the inner section of the openings 14 and 15. It is at the opening 1 1 that the valve 1 (i.e., the body 10 thereof) is connected to the opening 4 of the duct 2. More precisely, the duct 2 is, preferably, at least partially inserted in to the opening 1 1 at the opening 4 thereof. More preferably, the opening 4 (of the duct 2) is externally threaded and the opening 1 1 (of the valve 1 ) is internal ly threaded so that the two openings 4 and 1 1 can be screwed one into the oth er, so as to be vertically coaxial. Said screwing reversibly connects the valve 1 to the duct 2. Incidentally, the adverb "reversibly" means that the valve 1 can be connected to the duct 2 and can be disconnected from the latter an indefinite number of times. As it may be noticed in Figure 1 , the cross section of the open ing 4 has an inner diameter preferably greater than that of the cross section of the connection path 14. The opening 12, as well as the opening 1 1 , is prefera- bly, but not necessarily, internally threaded, so as to allow a reversible connec tion between the valve 1 and a possible second duct at the opening 12.

The valve 1 comprises a plug 20 housed in the chamber 13 and movable be tween a first opening position, at which it does not obstruct any of the connec- tion paths 14 and 15 (as shown in Figure 4), and a second closing position, at which it sealingly obstructs the connection path 15 (as shown in Figures 1 to 3). The plug 20 is preferably shaped like a disk having a diameter greater than that of the connection path 15 but lower than the inner diameter of the cross section of the chamber 13. The connection path 15 is obtained at a base 21 which de- limits the bottom of the chamber 13. When the plug 20 is in the opening posi tion, it is at an intermediate level between the connection paths 14 and 15, so that the liquid 6 can flow from the opening 1 1 into the opening 12 through the chamber 13, to be led inside the tank 3. When the plug 20 is in the closing posi tion, the plug 20 sealingly abuts against the base 21 about the connection path 15, preferably coaxially with the latter, so that the liquid 6 is retained in the chamber 13. The seal between the plug 20 and the base 21 is preferably achieved by interposing therebetween an annular gasket 22, such as, for ex ample, an O-ring. The gasket 22 is housed in an annular seat obtained in the base 21 around the connection path 15 preferably coaxially with the latter. Since the gasket 22 must be interposed between the plug 20 and the base 21 when the plug 20 is in the closing position, the seat of the gasket 22 has a di ameter smaller than that of the plug 20.

As it may be noticed in Figure 1 , the valve 1 is connected to the duct 2 so that the liquid 6 tends to send the plug 20 in abutment against the base 21. In other words, the valve 1 is connected to the duct 2 so that, when the plug 20 is in the closing position, an overpressure at the opening 1 1 with respect to the opening 12 (due to the pressure of the liquid 6 in the duct 2) applies a force on the plug 20 tending to keep the latter in the closing position, i.e., sealingly in abutment against the base 21.

The valve 1 preferably comprises a pair of rods 23 and 24 which extend central ly and orthogonally from the plug 20, starting from mutually opposite faces thereof. More precisely, the rod 23 rises from the plug 20 towards the opening 11 and has a length such as to cross the connection path 14 regardless of the position of the plug 20 in the chamber 23, i.e., also when the plug 20 is in the closing position (as shown in Figure 1 ). By centrally raising from the plug 20, the rod 23 is preferably coaxial to the connection path 14. Similarly, the rod 24 ex- tends from the plug 20 towards the opening 12 and has a length such as to cross the connection path 15 regardless of the position of the plug 20 in the chamber 23, i.e., also when the plug 20 is in the opening position (as shown in Figure 4). By centrally extending from the plug 20, the rod 24 is preferably coax ial to the connection path 15. The rods 23 and 24 keep the plug 20 "centered" with respect to the chamber 13 and to the connection path 15.

In order to ensure a correct positioning of the plug 20 with respect to the con nection path 15, upon a movement of the plug 20 from the opening position to the closing one, the valve 1 preferably further comprises a centering disk 25, in tegrally connected to the plug 20, coaxially to the latter, in an intermediate posi- tion between the plug 20 and the rod 24. The disk 25 has a diameter preferably smaller than that of the plug 20 and of the seat for housing the gasket 22, but greater than that of the connection path 15. The disk 25 can be housed in a seat 26 made in the base 21 at a section of the connection path 15 adjacent to the chamber 13. In other words, the seat 26 is crossed by the connection path 15 and is laterally delimited by a cylindrical wall preferably coaxial to said path.

The disk 25 is shaped so as to correspond to the cylindrical wall delimiting the seat 26. In particular, the disk 25 can be housed in the seat 26 so as to corre spond to said cylindrical wall. The seat 26 is in a position such that a housing of the disk 25 in the seat 26 (so as to correspond to the cylindrical wall laterally de- limiting the latter) determines the positioning of the plug 20 in the closing posi tion. In light of the foregoing, the disk 25 and the seat 26 act as centering means from the plug 20, with respect to the connection path 15, upon a move ment thereof from the opening position to the closing one.

The valve 1 preferably, but not necessarily, comprises a spring 27 elastically compressed between the plug 20 and a base 28 which delimits the top of the chamber 13. The base 28 is opposite to the base 21 and is crossed by the con nection path 14. The spring 27, preferably helical, is longitudinally crossed by the rod 23 and is preferably coaxial to the latter. The spring 27 applies a force on the plug 20 tending to move the latter from the opening position to the clos ing one.

The movement of the plug 20 between the opening and closing positions is op- erated by a lever 30, preferably of the first-class type, having a fulcrum 31 at the opening 12. The lever 30 is connected to a pair of floaters 32 and 33 at a first arm 34 thereof (on the right of the fulcrum 31 in Figure 1 ), and is in contact with the rod 24 at a second arm 35 thereof opposite to the arm 34 (on the left of the fulcrum 31 in Figure 1 ). The lever 30 is therefore in contact with the plug 20 by means of the rod 24 and the disk 25. More precisely, when an overpressure is present at the opening 1 1 with respect to the opening 12, said overpressure ap plies on the plug 20 a force tending to press the rod 24 against the arm 35, i.e., a force tending to press the plug 20, by means of the rod 24 and the disk 25, against the arm 35.

The floater 32, previously identified with the term "first floater", is integrally con nected to the arm 34 so that, when the floater 32 is at least partially immersed in the liquid 6 so as to undergo an Archimedes' thrust (as shown in Figure 1 ), said Archimedes' thrust generates on the lever 30, by means of the floater 32, a torque tending to rotate the lever 30 (about the pin 31 ) so as to move the plug 20, or allow the movement thereof, from the opening position to the closing po sition.

The floater 33, previously identified with the term "second floater", is connected to the arm 34 by means of a cord 36. More precisely, the latter is connected to the arm 34 at a first end 37, and to the floater 33 at a second end 38 opposite to the end 37. The cord 36 is connected to the arm 34 and to the floater 33 so that, when the cord 36 is tensioned due to the effect of the weight force acting on the floater 33, possibly reduced by the Archimedes' thrust undergone by said floater 33 when the latter is at least partially immersed in the liquid 6 (as shown in Fig ure 4), said tension generates on the lever 30 a torque tending to rotate the lat- ter (about the fulcrum 31 ) so as to move the plug 20 from the closing position to the opening position.

The floater 33 is suitably ballasted. More precisely, the floater 33 is ballasted so that, when:

• the plug 20 is in the closing position (i.e., the valve 1 is closed),

• an overpressure is present at the opening 1 1 with respect to the opening 12,

• said cord 36 is tensioned, and

• said tension reaches a limit value which is equal to or lower than the tension due to the sole weight force acting on the floater 33,

the torque generated on the lever 30 by said tension and by the weight force acting on the floater 32 and on the lever 30 (i.e., on the arm 34) is sufficiently strong to open the valve 1 , i.e., to make the lever 30 rotate so as to move the plug 20 from the closing position to the opening position, overcoming the force applied on the plug 20 by said overpressure.

The weight of the lever 30 (i.e., of the arm 34) and of the floater 32 is such that:

• when:

- the plug 20 is in the closing position (i.e., the valve 1 is closed),

- an overpressure is present at the opening 1 1 with respect to the opening 12, and

- the cord 36 is not tensioned,

the weight force acting on the lever 30 (i.e., on the arm 34) and on the floater 32 generates a torque on the lever 30:

- tending to open the valve 1 , i.e., tending to rotate the lever 30 (about the fulcrum 31 ) so as to move the plug 20 from the closing position to the opening position,

but

- not sufficiently strong to open the valve 1 , i.e., not sufficiently strong to make the lever 30 rotate so as to move the plug 20 from the closing posi tion to the opening position,

so that the plug 20 remains in the closing position due to the force applied thereto by said overpressure,

and

• when:

- the plug 20 is in the opening position (i.e., the valve 1 is open), - an overpressure is present at the opening 1 1 with respect to the opening 12, and

- the cord 36 is not tensioned,

the weight force acting on the lever 30 (i.e., on the arm 34) and on the floater 32 generates a torque on the lever 30

- tending to keep the valve 1 open, i.e., tending to keep the plug 20 in the opening position,

and

- sufficiently strong to keep the valve 1 open, i.e., sufficiently strong to keep the plug 20 in the opening position, thus overcoming the force applied thereto by said overpressure.

In light of this, the valve 1 is of the "direct-operated" type, in which the move ment of the plug 20 is operated by the lever 30.

The description of the valve 1 is now completed; the operation thereof, starting from a configuration (shown in Figure 1 ), is described below, in which:

• the valve 1 , at the opening 1 1 , is connected to the opening 4 of the duct 2;

• in the duct 2 there is liquid 6 under pressure;

• the plug 30 is in the closing position (i.e., the valve 1 is closed);

• the cord 36 is not tensioned;

· the tank 3 is "filled" with liquid 6, i.e., the filling level of the tank 3 is such that both floaters 32 and 33 float in the liquid 6 at the free surface thereof.

In this configuration an overpressure is present at the opening 1 1 with respect to the opening 12. Said overpressure therefore applies on the plug 20 a force tending to keep the latter in the closing position.

Figure 2 shows the valve 1 following the starting of a process for emptying the tank 3. Due to said emptying, the level at which the free surface of the liquid 6 in the tank 3 is progressively decreases, making the floater 32 emerge from the liquid 6. In the configuration shown in Figure 2, the cord 36 is not yet tensioned and the floater 32 is kept suspended by the lever 30. This is a consequence of the fact that, as specified above, when the plug 20 is in the closing position and the cord 36 is not tensioned, the weight force acting on the lever 30 and on the floater 32 generates on the lever 30 a torque which is not sufficiently strong to open the valve 1.

Figure 3 shows the valve 1 in an instant following that of Figure 2, in which the filling level of the tank 3 is such as to make the opening of the valve 1 imminent. More precisely, in the configuration of Figure 3 the valve 1 is still closed but the free surface of the liquid 6 is lowered to the point of tensioning the cord 36.

As shown in Figure 4, when the filling level of the tank 3 decreases to the point that the floater 33 emerges from the liquid 6, the weight force acting on the floater 33 generates on the lever 30 a torque sufficiently strong to open the valve 1. Following the opening of the valve 1 , new liquid 6 comes out of the duct 2, into the tank 3.

Incidentally, the valve 1 comprises a stop (not shown in the Figures) against which the lever 30 abuts with a rotation thereof that determines the passage of the plug 20 from the closing position to the opening one. By way of explanation, said stop consists of a groove made in the body 10 at the opening 12 starting from the opening of the latter. In said groove the arm 35 (of suitable length) can slide with a rotation of the lever 30. In other words, when the plug 30 is in the opening position, the arm 35 abuts against the bottom of said groove.

Supposing now the emptying of the tank 3 is interrupted, the latter begins to fill up. Due to this, the level of the floater 33 rises, together with the raising of the free surface of the liquid 6 in the tank 3. Even if the cord 36 ceases to be ten sioned as a result of the raising of the floater 33, the valve 1 remains open since, as specified above, when the plug 20 is in the opening position and the cord 36 is not tensioned, the weight force acting on the lever 30 and on the floater 32 generates on the lever 30 a torque sufficiently strong to keep the valve 1 open. When the liquid 6 in the tank 3 reaches the floater 32, the latter rises making the lever 30 rotate and closing the valve 1 (i.e., ceasing to oppose the overpressure at the opening 11 with respect to the opening 12).

In light of the foregoing, when the valve 1 is connected to a duct 2 which intro duces a liquid 6 inside a tank 3, the valve 1 is adapted to open only when the filling level of the tank 3, during an emptying thereof, has reached a determined lower limit which depends on the length of the cord 36.

Figure 5 shows a valve 40 which differs from the valve 1 in that it comprises, instead of the disk 25, a centering element 41 , substantially frustoconical and integrally connected to the plug 20, coaxially with respect to the latter, at the long base thereof, in an intermediate position between the plug 20 and the rod 24. More precisely, the rod 24 is integrally connected to the element 41 at the short base of the latter. The long base of the element 41 has a diameter prefer ably smaller than that of the plug 20 and of the seat for housing the gasket 22, but greater than that of the connection path 15. More preferably, the long base of the element 41 has a diameter equal to that of the disk 25. As well as the lat ter, the element 41 can be housed in the seat 26. The element 41 is further shaped so as to correspond to the cylindrical wall delimiting the seat 26 at least at the long base thereof. In particular, the element 41 can be housed in the seat

26 so as to correspond to said cylindrical wall at the long base thereof. The seat 26 is in a position such that a housing of the element 41 in said seat 26 (so as to correspond to the cylindrical wall laterally delimiting the latter) determines the positioning of the plug 20 in the closing position.

According to a variant of the valve 1 or 40, the plug 20 or 41 and the seat for housing the gasket 22 are shaped so that, when the plug 20 or 41 is in the clos ing position, the gasket 22, instead of being compressed longitudinally, is com pressed radially. If said variant is a variant of the valve 1 , the gasket 22, when the plug 20 is in the closing position, is preferably compressed between two concentric cylindrical walls. If said variant is a variant of the valve 40, the gasket 22, when the plug 41 is in the closing position, is preferably compressed be tween a cylindrical wall (of the seat for the housing thereof) and a frustoconical wall (of the plug 41 ).

According to the description provided for a preferred embodiment, it is apparent that certain changes may be introduced by those skilled in the art without de parting from the scope of the invention as defined by the following claims.