Field of application of the invention

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

Overview of the background art

Check valves operated by a first-class are widely used in various technological areas. One of the most common uses of valves of this type is the reversible occlusion of a delivery duct to regulate the introduction of a liquid (e.g. water) into a tank. In this particular application, 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 move the plug away from its seat, opening the valve. The lever which moves 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 to which by the floater is subject as a result of the liquid possibly present in the tank tends to close the valve, opposing the pressure of the liquid in the delivery duct. When the tank is full, the floater orients the lever so that it presses the plug against its seat, so that the valve is closed. When the tank is emptied, the aforesaid the Archimedes' thrust is lost and the lever, due to the pressure applied on the plug by the liquid in the delivery duct, rotates around the fulcrum moving the plug away from its seat 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 its seat when the tank is full. However, this is a disadvantage because the valve opens regardless of the tank fill level if the floater is released from the lever. Since check valves of the above type are mainly installed in the toilet flush tanks, the detachment of the floater from the lever can cause significant problems.

To overcome this drawback, the Applicant has designed a new type of check valve the operation of which is the reverse of that described above. More precisely, in check valves of this second type (object of Italian patent application for utility model no. ME201411000004 corresponding, in the new format, to no. 202014902237198) the inlet opening of the valve is connectable to the outlet opening of a pressure duct so that the plug is pressed against its seat 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 together as a whole have a weight such that the weight force acting on them, 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 empty, since the Archimedes' thrust on the floater is lost, the weight of the lever and the floater makes the lever rotate around the fulcrum, moving the plug away from its seat and opening the valve.

In this second type of valve, since the liquid in the delivery duct presses the plug against its seat, the valve remains advantageously closed if the floater detaches from the lever.

A valve according to one of the two types illustrated above connected to a delivery duct which introduces a liquid into a tank will be considered. Starting from a configuration in which the tank is full, and the valve is closed if the tank starts emptying, the valve opens by the effect of the pressure of the liquid contained in the delivery duct or by the effect of the weight of the floater. This may be a problem if a given volume of liquid is desired to be emptied from the tank before the tank filling process begins. To overcome this drawback, the Applicant has devised a further type of check valve which is the subject of the PCT patent application published under WO 2020 148790 A1. In the check valves of this third type, the inlet opening of the valve can be connected to the outlet opening of a pressure duct so that the plug is pressed against its seat 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 plug is operated by a first-class lever connected to two floats, one of which is ballasted. More precisely, the first floater is integrally connected to the lever at a first arm of the lever. The second floater, ballasted, is connected to said first arm by means of a cord. The lever is in contact with the plug at a second arm thereof opposite to said first arm. An Archimedes' thrust acting on the first floater, when it is partially immersed in a liquid, tends to move the plug to close the valve. The weight force acting on the second floater, when it is not immersed in said liquid, tends to move the plug to open the valve. The lever and the first floater have, as a whole, a weight such that the weight force acting on them, in the absence of the Archimedes' thrust on the first floater, is not sufficiently strong to open the valve when it is closed, but sufficiently strong to keep the valve open when it is open. The second floater is ballasted so that, when the cord is taut, the weight force acting on the lever and on the two floats is sufficiently strong to overcome the pressure applied on the plug by the liquid in the delivery duct, opening the valve. In light of the above, when the tank is full, both floats are supported by the Archimedes' thrust and the pressure of the liquid in the delivery duct keeps the valve closed. When the tank empties to the point that the Archimedes' thrust on the second floater is lost, the weight of the lever and both floats causes the lever to rotate around the fulcrum, pulling the plug away from its seat and, consequently, opening the valve.

The Applicant has encountered a problem that can arise when the valves of the above second and third types are used. Whenever the floater (in valves of the second type, or the "first" floater in valves of the third type) closes the valve abruptly as a result of the Archimedes' thrust acting on it added to an excessive overpressure in the delivery duct to which the valve is connected, this causes the phenomenon known as "water hammer". This phenomenon consists in the instantaneous arrest of the water column moving in the duct which, impacting on the plug, causes a considerable increase in pressure and creates a shock wave which, rebounding, causes a vacuum which can lead to the reopening of the valve and then again to its closure with the shock wave returning in a very rapid pendulum effect until it is damped. Furthermore, the damage caused by small or large water hammers is also well known.

Object of the invention

It is the purpose of the present invention to overcome the aforesaid drawbacks by indicating a check valve which, besides being suited to open only when the filling level of the tank, during an emptying thereof, reaches a given lower limit (like the known valves of the third type), does not reopen undesired due to the phenomenon of water hammer (as illustrated above), nor is there any known damage due to water hammer.

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

Summary and advantages 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 pressure 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 said duct);

• 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 the plug sealingly obstruct said second 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 relative 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 first actuating means comprising:

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

- a first element suited to float, at least partially, at the free surface of said liquid (by the effect of the Archimedes' thrust) when said first element is at least partially immersed in said liquid. Said first element suited to floating will be identified hereafter in this description as a "floater".

Said floater being integrally connected to said lever so that, when said floater is at least partially immersed in said liquid to be subject to an Archimedes’ thrust, said Archimedes’ thrust generates a first torque on said lever by means of said floater, tending to rotate said lever to move, or allow the movement of said plug from said opening position to said closing position, wherein, according to the invention, said moving means further comprise:

- a second element acting by force of its own weight. Said second element will be identified hereafter in this description as "ballast";

- a cord connected to said lever at a first end, and to said ballast at a second end opposite to said first end. As an alternative to the cord, it is possible to use another flexible element of extended length (such as a chain) suited to connect the lever and the ballast. Hereafter and in the following description, the word "cord" is intended to identify any flexible element extended in the length of the aforesaid type.

Said ballast having a weight such that, when it is immersed in said liquid, the weight force acting on said ballast is greater than the Archimedes’ thrust to which it is subjected, thus causing said ballast to sink in said liquid, said cord being tensioned due to the weight force acting on said ballast, possibly reduced by the Archimedes’ thrust to which said ballast was subjected when the latter is at least partially immersed in said liquid, said cord being connected to said lever so that the tension of said cord generates a second torque on said lever, tending to rotate said lever to move said plug from said closing position to said opening position, the weight force acting on said lever and on said floater generating a third torque on said lever, tending to rotate said lever to move said plug from said closing position to said opening position, said floater, said lever and said ballast mainly having, as a whole, such a weight that:

• when:

- said plug is in said closing position,

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

- said ballast is immersed in said liquid,

(regardless of whether or not said floater is immersed, even partially, in said liquid) said third torque, together with said second torque, is not sufficiently strong to rotate said lever to move said plug from said closing position to said opening position, so that said plug remains in said closing position by the effect of the force applied on it by said overpressure;

• when:

- said plug is in said opening position,

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

- said floater is not in contact with said liquid (so as not to be immersed therein, even partially),

(regardless of whether or not said ballast is immersed, even partially, in said liquid) said third torque, together with said second torque, is sufficiently strong to keep said plug in said opening position overcoming the force applied thereon by said overpressure;

• when:

- said plug is in said closing position,

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

- said floater is not in contact with said liquid (so as not to be immersed therein, even partially), and

- the 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 ballast, said third torque, together with said second torque, is not sufficiently strong to rotate said lever to move said plug from said closing position to said opening position, overcoming the pressure applied on said plug by said overpressure, said floater being shaped so that, when:

• said plug is in said opening position,

• said inlet opening is connected to said duct with an overpressure at said inlet opening relative to said outlet opening,

• said floater is at least partially immersed in said liquid, and

• said ballast is immersed in said liquid, said first torque is sufficiently strong to rotate said lever to move, or allow to move, said plug from said opening position to said closing position, overcoming (together with the force applied on said plug by said overpressure) said second and third torque, a rotation of said lever, to move, or allow to move, said plug from said opening position to said closing position when said ballast is immersed in said liquid, being decelerated by the liquid above said ballast (relative to the case in which the ballast is not immersed in the liquid).

In other words, the floater is shaped so that, when it is at least partially immersed in said liquid to be subject to the Archimedes' thrust, said Archimedes' thrust, added to the effect of the force applied on said plug by said overpressure at the valve inlet, is greater than the weight force acting on said lever, on said floater and on said ballast (reduced by the Archimedes' thrust to which said bal- last is subjected, the latter being immersed in said liquid).

When the valve of the invention is connected to a delivery duct which introduces a liquid into a tank, the valve is suited to open only when the filling level of the tank, during emptying of the tank, reaches a given lower limit.

To understand this, a configuration in which the valve is closed, and the tank is full should be considered, i.e., the tank filling level is such that the ballast is completely immersed in the liquid and the floater is in contact with the latter, only partially immersed in said liquid at the free surface thereof.

By initiating a tank emptying process (e.g., by removing a cap which sealingly obstructs an opening at the bottom of the tank), the tank fill level will gradually decrease. As a result, the column of liquid above the ballast is reduced while the floater emerges from the liquid and is kept suspended by the lever. The above is a consequence of the fact that, as specified above, when the plug is in the closing position and the ballast is immersed in the liquid, the weight force acting on the lever, on the floater, and on the ballast, reduced by the Archimedes' thrust to which said ballast is subjected, generates a torque on the lever which is not sufficiently strong to open the valve. The latter remains closed until the ballast emerges from the liquid. More precisely, when the filling level of the tank decreases to the point that the ballast emerges from the liquid, at least partially, and the Archimedes' thrust on the ballast is lost, the weight force acting on the ballast generates a torque on the lever which is sufficiently strong to open the valve. As the valve opens, new liquid flows out of the delivery duct to which the valve is connected and enters the tank. Assuming that the tank emptying rate is greater than the tank filling rate, the ballast is held suspended by the lever above the free surface of the liquid in the tank.

We will assume stopping the emptying of the tank, e.g., by obstructing the aforementioned opening with the aforementioned cap. Therefore, the tank begins to fill. As a result of this, the free surface of the liquid in the tank rises until it reaches and exceeds the ballast. Also if the ballast is submerged by the liquid, the valve remains open because, as specified above, when the plug is in the opening position and the ballast is immersed in the liquid, the weight force acting on the lever, on the floater and on the ballast, also if reduced by the Archi- medes' thrust to which said ballast is subjected, generates a torque on the lever which is sufficiently strong to maintain the valve open. When the liquid in the tank reaches the floater, the floater rises, making the lever rotate and closing the valve.

The fact that the valve object of the invention is suited to open only when the filling level of the tank, during an emptying thereof, reaches a given lower limit, reduces the number of times the valve has to be opened and closed again and ensures a more effective replacement of the liquid. Therefore, the advantages both in terms of wear of mechanical components and liquid quality if the latter is, e.g., water, are apparent.

As specified above, when the valve is closed and the ballast is immersed in the liquid, the weight force acting on the lever, on the floater and on the ballast, reduced by the Archimedes' thrust to which said ballast is subjected, generates a torque on the lever which is not sufficiently strong to open the valve, while when the valve is open, the weight force acting on the lever, on the floater and on the ballast, even if possibly reduced by the Archimedes' thrust undergone by said ballast when the latter is immersed in the liquid, generates a torque on the lever which is sufficiently strong to keep the valve open. For the sake of clarity, this is a consequence of the fact that the overpressure at the valve inlet opening relative to the outlet opening when the valve is closed is significantly higher than when the valve is open. In other words, the force applied on the plug by the liquid in the delivery duct when the valve is closed is much greater than when the valve is open.

The weight of the ballast is such that, when it is immersed in the liquid, the weight force acting on the ballast prevails over the Archimedes' thrust to which the ballast is subjected. The weight force acting on the ballast thus keeps the cord taut, especially during the closing of the valve. The presence of a column of liquid (i.e. an incompressible fluid) above the ballast slows down the closing of the valve to the point of preventing the occurrence of water hammer in the duct to which said valve is connected and with it the undesired reopening of the latter (as illustrated with reference to the prior art). This "prevention mechanism" is self-balancing because the greater the impulse to which the ballast sub- merged in the liquid is subjected due to a water hammer principle, the greater the braking effect on the ballast by the liquid above it.

Other innovative features of the present invention are illustrated in the description which follows and mentioned in the dependent claims.

According to one aspect of the invention, said lever is a first-class lever, said floater and said ballast being connected to said lever at a first arm thereof, said plug being shaped so that, when said inlet opening is connected to said duct with an overpressure at said inlet opening relative to said outlet opening, 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, relative to said second connection path, with a movement of the plug from the opening position to the closing position.

Advantageously, the centering means ensure that the plug is correctly positioned relative to the second connection path with a movement of the plug from the opening position into the closing position. In other words, the centering means ensure that the plug positions itself to sealingly obstruct the second connection path with a movement of the plug from the opening position into the closing position.

According to another aspect of the invention, the centering means comprises:

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

• a substantially discoidal element integrally connected to said plug and shaped to correspond to said substantially cylindrical wall, said substantially discoidal element being at least partially housable in said seat to correspond to said substantially cylindrical wall, said seat positioned so that an at least partial housing of said substantially discoidal element in said seat, to correspond to said substantially cylindrical wall, defines an arrangement of said plug in said closing position (to sealingly obstruct said second connection path).

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

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

• a substantially frustoconical element integrally connected to said plug at the major base thereof, and shaped to correspond to said substantially cylindrical wall at least at the major base thereof, said substantially frustoconical element being at least partially housable in said seat to correspond to said substantially cylindrical wall at least at the major base thereof, said seat positioned so that an at least partial housing of said substantially frustoconical element in said seat, to correspond to said substantially cylindrical wall at least at the major base thereof, defines an arrangement of said plug in said closing position (to sealingly obstruct said second connection path).

Brief description of the figures

Further objects and advantages of the present invention will be apparent from the following detailed description of an example of embodiment of the same and from the accompanying drawings exclusively provided by way of non-limiting example, in which:

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

- figure 2 shows some components of the valve in figure 1 in greater detail;

- figure 3 shows a diagrammatic partial cross-section view of the valve of figure 1 closed during an emptying of the said tank;

- figure 4 shows a diagrammatic partial cross-section view of the valve of figure 1 during tank emptying, which opened as a result of the tank filling level dropping below a lower limit;

- figure 5 shows a diagrammatic partial cross-section view of the valve in figure 1 open during a filling of the tank; - figure 6 shows a diagrammatic partial cross-section of the valve in figure 1 at an instant in which the tank has filled to the point of causing the valve to close and an upward movement of the ballast as a result of the water hammer braking action;

- figure 7 shows a diagrammatic partial cross-section of the valve of figure 1 at an instant immediately following that of figure 6 with the ballast which has descended again to tension the wire;

- figure 8 shows a diagrammatic partial cross-section of some components of a variant of the valve of figure 1 in a configuration in which it is closed.

Detailed description of preferred embodiments of the invention

Hereinafter in the present description, a figure may be illustrated also with reference to elements not expressly indicated therein but indicated on other figures instead. The scale and proportions of the various illustrated elements do not necessarily correspond to the real values.

The figures 1 and 2 show 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 stretch thereof inside the tank 3, with the longitudinal axis arranged, by way of example, vertically. The opening 4 is preferably located near an upper wall 5 of the tank 3. A liquid 6, pressurized in the duct 2, can be introduced into the tank 3 through the opening 4. The valve 1 is connected to the duct 2 at the opening 4 to regulate a liquid supply 6 into the tank 3.

The valve 1 comprises a body 10 including an inlet opening 11 , an outlet opening 12 and a chamber 13 interposed between the openings 11 and 12 to create a connection between them. More specifically, the chamber 13 is communicating with the opening 11 at a first connection path 14 and is communicating with the opening 12 at a second connection path 15. The openings 11 and 12, as well as the chamber 13 and the connection paths 14 and 15, are preferably cylindrical and more preferably coaxial, with their longitudinal axis arranged, in the figures, vertically. Even more preferably, the openings 11 and 12 have a cross-sectional area of internal diameter less than that of the cross-section area of the chamber 13, but greater than that of the cross-section area of the con- nection paths 14 and 15. It is at the opening 11 that the valve 1 (i.e., the body 10 itself) is connected to the opening 4 of the duct 2. More specifically, the duct 2 is, preferably, at least partially engaged in the opening 11 at its opening 4 thereof. More preferably, the opening 4 (of the duct 2) is externally threaded and opening 11 (of the valve 1 ) is internally threaded so that the two openings 4 and 11 can be screwed into each other to be coaxial (vertically in the figures). Said screw connection reversibly connects the valve 1 to the duct 2. Incidentally, the adverb "reversibly" means that the valve 1 is connectable to the duct 2 and disconnectable from the latter an indefinite number of times. As can be seen in figure 1 , the inner diameter of the cross-section of the opening 4 is preferably larger than that of the cross-section of the connection path 14. The opening 12, like the opening 11 , is preferably, but not necessarily, internally threaded, to allow a reversible connection 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 between a first opening position, at which it does not obstruct any of the connection paths 14 and 15 (as shown in figures 4 and 5), and a second, closing position, at which it sealingly obstructs the connection path 15 (as shown in figures 1 to 3 and 6 to 8).

The plug 20 is preferably shaped like a disc having a diameter greater than the diameter of the connection path 15 but smaller than the inner diameter of the chamber cross-section 13. The connection path 15 is formed at a base 21 which delimits the bottom of the chamber 13. When the plug 20 is in the opening position, it is at an intermediate elevation between the connection paths 14 and 15, so that the liquid 6 can flow from the opening 11 into the opening 12 through the chamber 13, to flow inside the tank 3. When the plug 20 is in the closing position, the plug 20 sealingly abuts against the base 21 around the connection path 15, preferably coaxially to 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 an annular gasket 22, such as an O-ring, between them. The gasket 22 is housed in an annular seat formed in the base 21 around the connection path 15, preferably coaxially to the latter. Since the gas- ket 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 smaller diameter than that of the plug 20.

As can be seen in figure 1 , the valve 1 is connected to the duct 2 so that the liquid 6 tends to send the plug 20 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 11 relative 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 abutting against the base 21 .

Preferably, the valve 1 comprises a pair of rods 23 and 24 extending centrally and orthogonally from the plug 20 starting from mutually opposite faces thereof. More specifically, the rod 23 rises from the plug 20 toward the opening 11 and has a length such to cross the connection path 14 regardless of the position of the plug 20 in the chamber 13, i.e., even when the plug 20 is in the closing position (e.g. as shown in figure 1 ). By raising the rod 23 centrally from the plug 20, it is preferably coaxial to the connection path 14. Similarly, the rod 24 extends from the plug 20 toward the opening 12 and has a length such to cross the connection path 15 regardless of the position of the plug 20 in the chamber 13, i.e., even when the plug 20 is in the opening position (e.g. as shown in figure 4). By extending the rod 24 centrally from the plug 20, it is preferably coaxial to the connection path 15. The rods 23 and 24 keep the plug 20 "centered" relative to the chamber 13 and connection path 15.

To ensure correct positioning of the plug 20 relative to the connection path 15 at a movement of the plug 20 from the opening position into the closing position, the valve 1 preferably also comprises a centering disc 25 integrally connected to the plug 20 coaxially to the latter, at an intermediate position between the plug 20 and the rod 24. The diameter of the disc 25 is preferably smaller than that of the plug 20 and the housing of the gasket 22, but larger than that of the connection path 15. The disc 25 is housed in a seat 26 made in the base 21 at a stretch 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 delimited laterally by a cylindrical wall preferably coaxial to said path. The disc 25 is shaped to corre- spond to the cylindrical wall delimiting the seat 26. In particular, the disc 25 is housed in the seat 26 to correspond to said cylindrical wall. The seat 26 is in a position such that a housing of the disc 25 in the seat 26 (to correspond to the cylindrical wall laterally delimiting the latter) determines the placement of the plug 20 in the closing position. In light of the above, the disc 25 and the seat 26 act as centering means from the plug 20, relative to the connection path 15, to a movement thereof from the opening position into the closing position.

The valve 1 preferably, but not necessarily, comprises a spring 27 elastically compressed between the plug 20 and a base 28 delimiting the chamber 13 on top. The base 28 is opposite to the base 21 and is crossed by the connection path 14. The spring 27, preferably helical, is crossed longitudinally by the rod 23 and is preferably coaxial to the latter. The spring 27 applies a force on the plug 20 to move it from the opening position to the closing position.

The movement of the plug 20 between the open and closing positions is operated by a lever 30, preferably of the first-class, having a fulcrum 31 preferably at the opening 12. The lever 30 is connected to a floater 32 and a to ballast 33 at a first arm 34 thereof (to 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 (to the left of the fulcrum 31 in figure 1 ). Therefore, the lever 30 is in contact with the plug 20 by means of the rod 24 and the disc 25. More precisely, when overpressure is present at the opening 11 relative to the opening 12, said overpressure applies a force on the plug 20 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 disc 25, against the arm 35.

The floater 32 is integrally connected to the arm 34 so that, when the floater 32 is at least partially immersed in the liquid 6 to undergo the Archimedes' thrust, said Archimedes' thrust generates on the lever 30, by means of the floater 32, a torque (previously identified with the expression "first torque") tending to rotate the lever 30 (around the pin 31 ) to move the plug 20 or allow a movement thereof, from the opening position into the closing position.

The ballast 33 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 ballast 33 at a second end 38 opposite to the first end 37. The ballast 33 has a weight such that, when it is immersed in the liquid 6 (e.g. as shown in figure 1 ), the weight force acting on the ballast 33 is greater than the Archimedes’ thrust to which it is subjected, thus causing the ballast 33 to sink in the liquid 6. The cord 36 is tensioned by the effect of the weight force acting on the ballast 33, possibly reduced by the Archimedes’ thrust to which the ballast 33 was subject when the latter is at least partially immersed in the liquid 6. The cord 36 is connected to the arm 34 so that the tension of the cord 36 generates a torque (previously identified by the expression "second torque") on the lever 30 tending to rotate the lever 30 (around the fulcrum 31 ) to move the plug 20 from the closing position into the opening position.

The weight force acting on the lever 30 and the floater 32 generates a torque (previously identified by the expression "third torque") on the lever 30 tending to rotate the lever 30 (around the fulcrum 31 ) to move the plug 20 from the closing position into the opening position.

The weight of the lever 30, floater 32, and ballast 33 is such that:

• when (as shown in figures 1 and 7):

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

- an overpressure is present at the opening 11 relative to the opening 12, and

- the ballast 33 is immersed in the liquid 6, regardless of whether or not the floater 32 is immersed, even partially, the liquid 6, the aforesaid third pair, together with said second pair, is not sufficiently strong to open the valve 1 , i.e., is not sufficiently strong to cause the lever 30 to rotate to move the plug 20 from the closing position into the opening position, so that the plug 20 remains in the closing position by the effect of the force applied on it by said overpressure (and possibly by the spring 27, if present);

• when (as shown in figures 4 and 5):

- the plug 20 is in the opening position (i.e., the valve 1 is open),

- an overpressure is present at the opening 11 relative to the opening 12, and

- the floater 32 is not in contact with the liquid 6 (i.e. it is not immersed in it, not even partially), whether or not the ballast 33 is immersed, even partially, in the liquid 6, the aforesaid third pair, together with the aforesaid second pair, is sufficiently strong to keep the valve 1 open, i.e., is sufficiently strong to keep the plug 20 in the opening position by overcoming the force applied on it by said overpressure (and by the spring 27, if present);

• when:

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

- an overpressure is present at the opening 11 relative to the opening 12,

- the floater 32 is not in contact with the liquid 6 (i.e. it is not immersed in it, not even partially),

- the tension on the cord 36 reaches a limit value which is equal to or lower than the tension due only to the weight force acting on the ballast 33, the aforesaid second pair, together with the aforesaid third pair, is sufficiently strong to open the valve 1 , i.e., to make the lever 30 rotate to move the plug 20 from the closing position to the opening position by overcoming the force applied on the plug 20 by said overpressure (and possibly by the spring 27, if present).

The floater 33 is shaped so that, when:

• the plug 20 is in the opening position (i.e., the valve 1 is open),

• an overpressure is present at the opening 11 relative to the opening 12,

• the floater 33 is at least partially immersed in the liquid 6, and

• the ballast 33 is immersed in the liquid 6, the aforesaid first torque is sufficiently strong, rotate the lever 30 to move the plug 20, or allow it to be moved, from the opening position towards the closing position, thus overcoming the aforesaid second and third torques (together with the force applied on the plug by said overpressure and by the spring 27, if present).

In light of the foregoing, the valve 1 is of the "direct-operated" type, wherein the movement of the plug 20 is controlled by the lever 30. After describing the valve 1 , its operation will be illustrated below starting from a configuration (shown in figures 1 and 2) in which:

• the valve 1 , at the opening 11 , is connected to the opening 4 of the duct 2,

• there is pressurized liquid 6 in the duct 2,

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

• the tank 3 is only partially filled with liquid 6. More precisely, the filling level of the tank 3 is such that the floater 32 is not in contact with the liquid 6 (i.e., lies above the free surface of the liquid) and the ballast 33 is submerged in the liquid 6 (i.e., lies below the free surface of the liquid).

In this configuration, an overpressure is present at opening 11 relative to the opening 12 and the floater 32 is kept suspended by the lever 30. Said overpressure applies a force on the plug 20 to keep it in the closing position.

The figure 3 shows valve 1 and tank 3 following the starting of a process to empty the latter. As a result of this emptying, the height of the free liquid 6 in the tank 3 gradually decreases, causing the ballast 33 to emerge from the liquid 6. In the configuration in figure 3, the ballast is still partially submerged in the liquid 6.

The figure 4 shows the valve 1 and the tank 3 at an instant after the one in figure 3, in which the fill level of the tank 3 has dropped to the point of causing the valve 1 to open. More specifically, in the configuration of figure 4, the ballast 33 has completely emerged from the liquid 6. The loss of the Archimedes' thrust on the ballast 33 caused the aforementioned second pair, along with the third pair, to become sufficiently strong to open the valve 1 . In other words, the filling level of the tank 3, during the emptying of the latter, dropped to the point that the tension of the cord 36 reached the previously mentioned "limit value" (at which the aforementioned second and third pairs overcame the force applied on the plug 20 by the overpressure, opening the valve 1 ). As a result of the opening of valve 1 , new liquid 6 started to leak from the duct 2 into tank 3. In the configuration of figure 4, the emptying of the tank 3 occurs, by way of example, faster than the filling thereof by the liquid entering from the valve 1 . As a result of this, the free fluid surface 6 in the tank 3 is well below the ballast 33.

Incidentally, the valve 1 comprises a stop (not shown in the figures) against which the lever 30 strikes upon a rotation thereof which causes the valve plug 20 to move from the closing position into the opening position. By way of example, said retainer consists of a groove made in the body 10 at the opening 12 from the opening thereof. The arm 35 (of appropriate length) may slide at a rotation of the lever 30 in said groove. In other words, when the plug 30 is in the opening position, the arm 35 is abutting against the bottom of said groove.

Assuming that the emptying tank 3 is stopped, the tank will begin to fill. As a result of this, the free surface of the liquid 6 in the tank 3 rises. As shown in figure 5, the valve 1 remains open even if the ballast 33 is reached and exceeded by the free surface of the liquid 6 (so that it is submerged in the latter). Conversely, as shown in figure 6, when the liquid 6, in the tank 3, reaches the floater 32, the latter rises by rotating the lever 30 and closing the valve 1 .

In view of the foregoing, when the valve 1 is connected to a duct 2 which introduces a liquid 6 into a tank 3, the valve 1 is only suited to open when the filling level of the tank 3, during an emptying thereof, reaches a given lower limit which depends on the length of the cord 36.

The weight force acting on the ballast 33 keeps the cord 36 taut during the closing of the valve 1 . In particular, the presence of a column of liquid 6 above the ballast 33 slows the closing of the valve 1 to the point of preventing the occurrence of the water hammer phenomenon in the duct 2. At the instant in which the valve 1 closes, the ballast 33, due to inertia, continues its ascent slightly towards the free surface of the liquid 6 (as shown in figure 6) and then descends again by tensioning the cord 36 (as shown in figure 7).

Figure 8 shows a valve 40 which differs from the valve 1 in that it comprises a substantially frustoconical centering element 41 instead of the disc 25, which is integrally connected to the plug 20, coaxially to the latter, at its major base, 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 minor base of the latter. The major base of the element 41 preferably has a diameter smaller than that of the plug 20 and the gasket housing seat 22, but larger than that of the connection path 15. More preferably, the major base of the element 41 has a diameter equal to that of the disc 25. Like the latter, the element 41 can be housed, at least partially, in the seat 26. The element 41 is further shaped to be able to correspond to the cylindrical wall delimiting the seat 26 at least at its major base. In particular, the element 41 can be housed in the seat 26 to correspond to said cylindrical wall at its major base. The seat 26 is in a position such that a housing of the element 41 in said seat 26 (to correspond to the cylindrical wall laterally delimiting the latter) determines the placement 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 housing seat of the gasket 22 are shaped so that, when the plug 20 or 41 is in the closing position, the gasket 22 is radially compressed instead of being longitudinally compressed. More specifically, the gasket 22, when the plug 20 or 41 is in the closing position, is preferably compressed between two concentric cylindrical walls (of the housing thereof and the plug 20 or 41 , respectively). Alternatively, the gasket 22, when the plug 20 or 41 is in the closing position, is preferably compressed between a cylindrical wall (of the plug housing) and a frustoconical wall (of the plug 20 or 41 ).

Based on the provided description of a preferred embodiment, it is apparent that changes may be introduced by a person skilled in the art without because of this departing from the scope of protection of the invention as defined by the following claims.