DESCRIPTION

Application field

The present invention refers to a check valve for the control of a hydraulic cylinder. In particular, the present invention refers to a check valve comprising a body, which extends along a longitudinal axis and is provided with at least one first opening and at least one second opening that allow the passage of a fluid into such body, the check valve comprising a seal blocking member that acts as closure means of the at least one second opening. The following description is made with reference to this application field with the only purpose of simplifying the exposition.

Prior art

As it is well known in this technical field, a check valve, also known as nonreturn valve, allows to block the passage of a fluid, for example hydraulic oil under pressure used in hydraulic applications. The check valve allows in particular the passage of the fluid in a direction and prevents its passage in an opposite direction.

Generally, as shown in Figure 1 , a check valve 1 comprises a body 2 in turn including a plurality of components that allow the passage of the fluid from a first opening 3A to a plurality of second openings 3B, and prevent its passage in the opposite direction.

The check valve 1 can be used to control a hydraulic cylinder installed in machines that require a mechanical drive, such as for example earthmoving machines, elevators, or tractors. In many applications, an equipment that allows the application of a mechanical force is generally connected to one end of the hydraulic cylinder.

In particular, as shown in Figure 2, the check valve 1 is generally associated with a hydraulic cylinder 4 by means of suitably pipes and connection fittings 5, which allow the passage of fluid within such cylinder 4. Generally, the check valve 1 is connected externally to the hydraulic cylinder 4 and for this reason it needs a protective structure 6 that protects the valve, the pipes and the connection fittings 5 from possible impacts and damages that may occur during the use of the hydraulic cylinder 4. The protective structure 6 usually extends from the ends of the hydraulic cylinder 4 so as to surmount the check valve 1. This solution has the drawback that, in spite of the presence of the protective structure 6, in some cases the connection pipes 5 and the check valve 1 itself are hit and can break causing dangerous situations for a user, as well as damages to tools connected to the hydraulic cylinder 4. The failure obviously causes also an interruption of the operation of the machine to which the hydraulic cylinder is connected, with subsequent economic losses.

Furthermore, the use of components external to the hydraulic cylinder 4 leads to considerable space constraints that hinder many applications of such a cylinder. Moreover, the second openings 3B of the check valve 1 are generally circular holes whose diameter is large enough to allow the valve to be used with different fluid flows, without the possibility to precisely control such flow.

Although being widely used, this solution has the drawback that when the check valve 1 is used to control cylinders subjected to predetermined loads, such as in the case of double-acting cylinders used in a three-point hitch, the fluid flowing through the second openings 3B of the check valve 1 generally has a flow rate so high that it is not easily controllable, leading to a non-optimal operation of the valve itself. As a consequence, the loads connected to the cylinder may become unstable. Essentially, cavitation phenomena can occur within the hydraulic cylinder 4, leading to an intermittent operation of the check valve 1.

For this reason, as shown in Figure 2, it is known to connect a flow controller 7 to the second openings 3B of the check valve 1 , for example a throttle, so as to allow a more precise control of the flow of the fluid. This is also aimed at allowing a slow movement of the hydraulic cylinder 4, guaranteeing the safety of the user.

As a consequence, a double-acting hydraulic cylinder 4 normally comprises both the check valve 1 and the flow controller 7 arranged within the cylinder 4 itself, which leads to the above-mentioned drawbacks. The technical problem of the present invention is to provide a check valve having structural and functional features such as to allow overcoming the limitations and drawbacks still affecting the known solutions, in particular able to control the flow of fluid flowing through one opening thereof without requiring the presence of an additional component or a component external to the valve, so that the valve can easily be integrated into a component of a hydraulic cylinder.

Summary of the invention

The solution idea at the basis of the present invention is to devise a check valve wherein at least one opening, for example the outlet opening, is suitably calibrated by reducing the area of the cross-section thereof, such reduction being performed according to the pressure and the flow rate required for a fluid flowing through said opening. In this way, the check valve is suitably integrated into the end cap of a hydraulic cylinder which is controlled by such a valve.

On the basis of such solution idea, the above technical problem is solved by a check valve for a hydraulic cylinder, the check valve comprising a body, which extends along a longitudinal axis and is provided with at least one first opening and at least one second opening that allow the passage of a fluid into that body, the check valve comprising a seal blocking member that acts as closure means of the at least one second opening, such a check valve being characterized in that the at least one second opening is calibrated by reducing the area of the cross section thereof as a function of the pressure and of the nominal flow rate required for a fluid flowing therethrough.

More in particular, the invention comprises the following additional characteristics, taken individually or in combination if required.

According to an aspect of the present invention, the relationship between the area of the cross section of the at least one second opening and the flow rate of the fluid flowing through the at least one second opening can be given by:

Q = Ak^(2Ap/p) where Q is the flow rate of the fluid flowing through the second opening, A is the sectional area of the second opening, k is a characteristic flow coefficient of the check valve, Δρ is the pressure difference upstream and downstream of the second opening, and p is the fluid density.

According to an aspect of the present invention, the at least one second opening can have a cross section whose area is less than or equal to at least 7 mm ² .

According to another aspect of the present invention, the check valve can comprise a plurality of second openings, the sum of the sectional areas of the second openings being less than or equal to at least 7 mm ² . Alternatively, the check valve can comprise only one second opening.

According to an aspect of the present invention, the at least one second opening can have a cross section whose area ranges from 0.2 mm ² to 5 mm ² .

According to another aspect of the present invention, the at least one second opening can have a circular shape.

According to another aspect of the present invention, the seal blocking member can be a sphere apt to slide in a cavity which has preferably a cylindrical shape and is formed within the body of the check valve.

According to another aspect of the present invention, the seal blocking member can be constantly urged into closed position by an elastic member, such an elastic member being pressed on the occasion of the passage of fluid coming from the at least one first opening or on the occasion of external driving of the check valve, for example by means of a driving piston.

Furthermore, the at least one second opening can be a transversal through opening of the body of the check valve, the seal blocking member abutting onto a shoulder to accomplish the seal closure of the at least one second opening.

The present invention also refers to a component for a hydraulic cylinder, such a component comprising ducts for the passage of a fluid therethrough, the component being characterized in that it comprises at least one check valve of the kind described above, the check valve being integrated into such a component. According to a preferred embodiment, the component can be an end cap of a hydraulic cylinder.

Furthermore, the component can comprise connecting means adapted to allow a seal connection with a hydraulic cylinder. According to an aspect of the present invention, the connecting means can be a thread, or a flange, or a plurality of tie rods.

According to another aspect of the present invention, the component can comprise attaching means apt to connect such a component with external pipes for the feeding and/ or the discharge of fluid. According to another aspect of the present invention, the component can comprise a check valve of the kind described above, as well as a further check valve, those check valves being driven by at least one piston which is arranged therebetween.

According to another aspect of the present invention, the check valve and the further check valve can be integrated into a single component.

The present invention also refers to a hydraulic cylinder comprising a main body that extends along a longitudinal axis, the main body being hollow and slidingly housing a rod therein, at least one first chamber and at least one second chamber being defined within the main body, the hydraulic cylinder being characterized in that it comprises a component of the kind described above.

According to an aspect of the present invention, the component can be removably connected to the cylinder.

Alternatively, the component can be welded to the cylinder. According to an aspect of the present invention, the cylinder can be a double-acting cylinder. In this case, the at least one second opening can be a fluid inlet opening into the second chamber or a fluid outlet opening from the second chamber, the at least one second opening being adapted to reduce the flow rate of the fluid flowing therethrough. Alternatively, the at least one second opening can be a fluid inlet opening into the first chamber or a fluid outlet opening from the first chamber, the at least one second opening being adapted to reduce the flow rate of the fluid flowing therethrough.

Finally, generally, the present invention refers to a hydraulic cylinder comprising at least one check valve of the kind described above, the check valve being integrated into the cylinder. The features and advantages of the check valve, of the component, and of the cylinder according to the invention will become apparent from the following description of an embodiment thereof, given by way of non-limiting example with reference to the accompanying drawings.

Brief description of the drawings In those drawings:

- Figure 1 shows a schematic sectional view of a check valve according to the prior art;

- Figure 2 shows a schematic view of a hydraulic cylinder according to the prior art; - Figure 3 shows a schematic sectional view of a check valve according to the present invention;

- Figure 4A shows a schematic sectional view of an end cap of a hydraulic cylinder comprising the check valve of Figure 3;

- Figure 4B shows a schematic sectional view of a hydraulic cylinder comprising the end cap of Figure 4A; and

- Figures 5A-5C schematically show hydraulic diagrams of the operation of the cylinder of Figure 4B.

Detailed description

With reference to those figures, and in particular to the example of figure 3, a check valve for a hydraulic cylinder according to the present invention is globally and schematically indicated with 10.

It is worth noting that the figures represent schematic views and are not drawn to scale, but instead they are drawn so as to emphasize the important features of the invention. Moreover, in the figures, the different elements are depicted in a schematic manner, their shape varying depending on the application desired. It is also noted that in the figures the same reference numbers refer to elements that are identical in shape or function.

The check valve 10 of the present invention is applied in the control of mechanical actuators of particular machines, such as hydraulic cylinders mounted on earthmoving machines, elevators, tractors or similar apparatuses requiring mechanical handling. By ways of a nonlimiting example, the check valve 10 can be used to adjust the operation of a strut included in a three-point hitch of a tractor, i.e. the so-called 3 ^rd point hitch of a tractor, as will be illustrated in greater detail later.

The check valve 10 is structured in such a way to allow the passage of a fluid, for example of hydraulic oil, in a direction and to prevent its passage in an opposite direction.

As shown in Figure 3, the check valve 10 comprises a body 1 1 that extends along a longitudinal axis H-H, such body 1 1 defining a chamber 1 1 ' therein and being provided with at least one first opening 12A and with at least one second opening 12B, which allow the passage of the fluid within such chamber 1 1 ' along a fluid path. In the following, the second opening 12B is also defined as an outlet opening without limiting the scope of protection of the present disclosure, since this second opening can also be a fluid inlet opening.

In the example of Figure 3, the first opening 12A is a fluid inlet opening, while the second opening 12B is a fluid outlet opening. In other words, the fluid enters into the chamber 1 1 ' of the check valve 10 at the first opening 12 A, according to the direction indicated by the arrow A in Figure 3, and exits the chamber 1 1 ' at the second opening 12B, according to the direction indicated by the arrow B in Figure 3.

In the case of driven check valves (for example by means of a driving piston), the second opening 12B can also be a fluid inlet opening, as it will be shown below.

Furthermore, in the example of Figure 3, the first opening 12A is a longitudinal opening, i.e. it extends along the longitudinal axis H-H, while the second opening 12B is a cross-sectional or transversal opening, i.e. it extends in a direction orthogonal to the longitudinal axis H-H. The body 1 1 of the check valve 10 is preferably made of steel, even though it is possible to use other suitable materials.

The check valve 10 further comprises a seal blocking member or shutter 13 housed within the chamber 1 1 ' of the body 1 1 and able to move within the chamber 1 1 '.

In particular, the chamber 1 1 ' is preferably a cylindrical bore having an inner wall W that forms, in a first portion PI of the chamber 1 1 ', a guide for the seal blocking member 13. In other words, the seal blocking member 13 is free to slide along the longitudinal axis H-H in the cylindrical bore of the chamber 1 1 ' delimited by the inner wall W.

In a preferred embodiment of the present invention, the seal blocking member 13 is a sphere whose diameter substantially coincides with an inner diameter D l of the cylindrical bore in the first portion PI , the term diameter indicating herein a maximum transversal dimension. It is underlined that other shapes of the seal blocking member 13 are also possible, for example it is possible to provide a seal blocking member 13 substantially T-shaped.

The seal blocking member 13 is preferably made of steel.

Furthermore, the seal blocking member 13 is constantly urged into a closed position of the second opening 12B by an elastic member 14, such as for instance a spring, the seal blocking member 13 being connected to an end of such elastic member 14.

Furthermore, in a preferred embodiment of the present invention, the chamber 1 1 ' has at least one second portion P2 (adjacent to the first portion PI) having a second diameter D2 less than the first diameter D l , so that an abutment surface or step, which the seal blocking member 13 abuts onto, is defined within the chamber 1 1 '. In other words, the step between the portion PI and the portion P2 is a shoulder S which the seal blocking member 13 abuts onto. In particular, the seal blocking member 13 abuts onto the shoulder S when there is no fluid entering from the first opening 12A or when there is no enough pressure thereon of the fluid coming from the first opening 12A, i.e. when the check valve 10 is in a rest state. When the seal blocking member 13 abuts onto the shoulder S, it closes the second opening 12B and it is thus not possible that the fluid flows from the second opening 12B to the first opening 12A. In other words, in the rest state, the elastic member 14 places the seal blocking member 13 in abutment onto the shoulder S. The seal blocking member 13 thus acts as closure means of the second opening 12B.

Alternatively, once exceeded a certain pressure value of the fluid entering from the first opening 12 A (at least greater than the elastic force exerted by the elastic member 14), the seal blocking member 13 compresses the elastic member 14 and the fluid is free to flow from the first opening 12A to the second opening 12B, which is open due to the movement of the seal blocking member 13 that compresses the spring 14. In other words, the check valve 10 is unidirectional because, when it is not driven, it allows the fluid to flow in the direction indicated by the arrows A and B of Figure 3 and not in an opposite direction.

The seal blocking member 13 is thus able to control the fluid passage between the first opening 12A and the second opening 12B.

It should be noted that, in an alternative embodiment of the present invention (not shown in the figures), the shoulder S may also be absent, for example when the sealing is realized through appropriate seals.

In case the check valve 10 is driven by actuators (such as for example a driving piston), it is also possible to allow a fluid passage in the opposite direction, i.e. from the second opening 12B to the first opening 12A. In particular, such actuators can push the seal blocking member 13 and/ or press the elastic member 14 so that the seal blocking member 13 allows the fluid passage from the second opening 12B to the first opening 12A once it has moved.

In general, the first opening 12A preferably has a circular shape with a sectional area larger than 20 mm ² . The second opening 12B preferably has the shape of a circular hole, even though other shapes are obviously possible.

Advantageously according to the present invention, the dimensions of the second opening 12B are suitably calibrated, i.e. the second opening 12B has a reduced cross-sectional area, in order to adjust the speed, and thus the flow rate, of the fluid flowing through such second opening 12B.

The term "calibrated opening" indicates an opening whose dimensions are selected as a function of the working pressure of the fluid and as a function of the flow rate required for the fluid flowing therethrough, wherein such values may vary according to the desired application, in particular according to the hydraulic cylinder to which the valve is associated.

The second opening 12B is suitably calibrated by reducing the area of its cross section as a function of the pressure and of the nominal flow rate required for a fluid flowing therethrough, such values being linked by the following relation:

Q = AkJ(2 p/p) where Q is the flow rate of the fluid flowing through the second opening 12B, A is the area of the cross-section of the second opening 12B, k is the characteristic flow coefficient of the valve, Δρ is the pressure difference upstream and downstream of the second opening 12B, and p is the fluid density. As an example, the parameter k, which mainly depends on the geometry of the valve, can generally vary from 0.6 to 1 , such example being however not limitative of the scope of the present invention. In particular, experimental studies performed by the Applicant have shown that, when used for the control of a hydraulic cylinder, the check valve 10 has an optimal operation when the second opening 12B has a cross section whose area is substantially less than or equal to at least 7 mm ² .

This is equivalent to a second opening 12B having a circular section whose diameter is substantially less than or equal to at least 3 mm.

The same effect can also be obtained by a check valve 10 that comprises, in an alternative embodiment of the present invention, a plurality of second openings 12B, the sum of the cross-sectional areas of those second openings 12B being substantially less than or equal to at least 7 mm ² . Even more preferably, an optimal operation of the check valve 10 is obtained when the second opening 12B has a cross section whose area is substantially comprised between 0.2 mm ² and 5 mm ² . This is equivalent to an opening having a circular section whose diameter is substantially comprised between 0.5 mm and 2.5 mm.

Even in this case, the same effect can be obtained by a check valve 10 comprising a plurality of second openings 12B, the sum of the sectional areas of those second openings 12B being substantially comprised between 0.2 mm ² and 5 mm ² .

As mentioned before, the area of the cross section of the second opening 12B is selected in order to adjust the flow rate of the fluid that flows through such opening according to the working pressure of the valve, those values varying according to the particular applications of the check valve 10.

As an example, considering a fluid pressure difference of about 150 bar, a circular second opening 12B having a diameter of 3 mm corresponds to an outlet flow rate from such opening of about 60 liters per minute, as well as a circular second opening 12B having a diameter of 2.5 mm corresponds to an outlet flow rate of about 42 liters per minute.

In the example of Figure 3, the second opening 12B is a transversal through opening of the body 1 1 of the check valve 10, wherein a distance h, measured along the longitudinal axis H-H, of the second opening 12B from the shoulder S is equal to about 1 mm. The reduction of the flow rate of the fluid flowing through the second opening 12B of the check valve 10 is advantageous, in particular when the check valve 10 controls the operation of hydraulic cylinders.

In fact, as observed before, the check valve 10 of the present invention is adapted to be connected to a hydraulic cylinder (such as for example a cylinder acting as an actuator for particular machines) in order to precisely control the operation thereof.

In particular, advantageously according to the present invention, the check valve 10 described above is integrated into a component of a hydraulic cylinder, such component being preferably an end cap of the hydraulic cylinder.

With reference to Figure 4A, an end cap of a hydraulic cylinder according to the present invention is globally and schematically indicated with 100. The end cap 100 comprises suitable ducts for the passage of the fluid and at least one check valve 10 of the type described above for the control and adjustment of the fluid passage therethrough.

Conveniently, the check valve 10 is integrated within the end cap 100, and it is therefore not arranged externally. Namely, the end cap 100 comprises suitable recesses so as to house at least one check valve 10, for example of the type illustrated in Figure 3 and in its relative description.

Specifically, the end cap 100 comprises at least one first duct 101 A connected to the first opening 12A of the check valve 10 integrated therein, as well as at least one second duct 10 IB connected to the second opening 12B of the check valve 10. Since the second opening 12B has a reduced area, the flow rate of a fluid flowing through it is consequently reduced, as previously described.

The end cap 100 is an end of a hydraulic cylinder 1000, which is schematically shown in Figure 4B.

In particular, the hydraulic cylinder 1000 comprises a main body 1001 extending along a longitudinal axis H'-H', the main body 1001 being hollow and slidingly housing a rod 1002 therein, the rod 1002 sliding through a head 1005, which is the end of the cylinder 1000 opposite to the end cap 100 along the longitudinal axis H'-H'.

One end of the rod 1002 is connected to a piston 1003 that receives and/ or exerts a push from/ on a hydraulic fluid within the cylinder, as it will be explained more in detail below.

Conveniently, the cylinder 1000 comprises the previously described end cap 100, which is associated with the main body 1001 thereof.

In particular, in an embodiment of the present invention, the end cap 100 is fastened to the main body 1001 of the cylinder 1000 by means of a seal welding.

Furthermore, in an alternative embodiment of the present invention, the end cap 100 is not welded to the cylinder 1000, but it comprises connecting means adapted to connect such end cap 100 to the main body 1001 of the hydraulic cylinder 1000, so that the end cap 100 and the hydraulic cylinder 1000 can be removably associated. As an example, the end cap 100 can comprise a thread for its screwing to the main body 1001 of the cylinder 1000, or it can be structured so as to be associated with the cylinder 1000 by means of a flange or tie rods, a suitable seal being interposed between the end cap 100 and the main body 1001 of the cylinder 1000 to ensure the fluid tightness of such cylinder 1000.

The piston 1003 defines at least two chambers within the main body 1001 of the cylinder 1000, namely a first chamber 1001 ' connected to the end cap 100 (also called "end cap-side chamber") and a second chamber 1001 " being opposite to the end cap 100 and to the first chamber 1001 ' with respect to the piston 1003 (also called "rod-side chamber"). Furthermore, the piston 1003 comprises suitable seals 1004 for the insulation of the first chamber 1001 ' from the second chamber 1001 ".

It should be noted that, in an alternative embodiment of the present invention (not shown in the figures), the check valve 10 may also be integrated into the head 1005 of the hydraulic cylinder 1000, even if in this case the constructive design of the cylinder would be more demanding.

In the following, the present invention will be illustrated in greater detail according to a preferred embodiment thereof wherein the hydraulic cylinder 1000 is a double-acting hydraulic cylinder, such as, for example, a hydraulic cylinder used as a strut of a three-point hitch of a tractor, and wherein the check valve 10 is integrated into the end cap 100 of such hydraulic cylinder 1000. However, the present example is not to be intended as limitative of the scope of the present invention and the hydraulic cylinder 1000 can be used in many other applications. In fact, the hydraulic cylinder 1000 may also be a single-acting cylinder, as further described below.

Referring again to Figures 4A and 4B, in the case of a double-acting cylinder, the end cap 100 of the cylinder 1000 comprises at least one check valve 10 according to the present invention and described above, and further comprises at least one second check valve, indicated as lObis in the figures, both valves being integrated into the end cap 100.

The second check valve lObis may be a check valve of the known type, i.e. not including a calibrated second opening 12B. The second check valve lObis may also be a check valve 10 according to the present invention. In the embodiment of Figures 4A and 4B, the end cap 100 comprises at least one third duct 102 A connected to a first opening of the check valve lObis integrated therein, and at least one fourth duct 102B connected to a second opening of this check valve lObis for the passage of fluid inside the hydraulic cylinder 1000, in particular, in the example of Figure 4B, inside the first chamber 1001 '.

In an alternative embodiment, the check valve 10 and the check valve 1 Obis can be integrated into a single component, such as a manipulable cartridge, which in turn is integrated into the end cap 100, such a single component being referred to as "double-acting pilot operated check valve", according to a well-known term used in this technical field.

Opportunely, also at least one driving piston 106 is integrated within the end cap 100, the driving piston 106 being arranged in order to drive both the check valves 10 and lObis, i.e. so as to drive the seal blocking members of the valves in an open position in opposition to the force exerted thereto by the elastic members. Obviously, in case the check valve 10 and the check valve lObis are integrated into a single component, also the piston 106 is integrated into such single component and is suitably arranged between the two check valves, so that it can alternatively act on both seal blocking members to open or close the two valves depending on the movement required to the cylinder.

Depending on the desired application, the fluid can be supplied both in the first chamber 1001 ' and in the second chamber 1001 " within the main body 1001 of the cylinder 1000, causing the rod 1002 to move in one or the other direction along the longitudinal axis H'-H' depending on the chamber in which the fluid is supplied.

In particular, the end cap 100 comprises attaching means 104 and 105, preferably in the form of threaded recesses, respectively connected to the first duct 101 A and to the third duct 102 A, to allow the connection of the end cap 100 to external pipes for the feeding of fluid coming from a pump and a control valve (or distributor) and / or for the discharge of fluid into a tank, depending on the operative conditions of the cylinder 1000. Furthermore, the second duct 10 IB is connected to a pipe 107 (or to another duct which can be for example partially embedded in the cylinder body) for the feeding and/ or the discharge of fluid into/ from the second chamber 1001.

The main body 1001 of the cylinder 1000 is preferably made of steel (or of any other suitable material), and the end cap 100 comprises a main body also made of steel (or of any other suitable material). As illustrated in Figure 5A, in the case of a double-acting cylinder used as a strut of a three-point hitch, in order to cause the movement of the rod 1002 towards the end cap 100, the fluid coming from a tank T is delivered by means of a pump P and a distributor D into the second chamber 1001 " of the cylinder 1000 passing through the check valve 10 according to the present invention, from the first opening 12A to the second opening 12B, so that the flow rate of the fluid entering this second chamber 1001 " is suitably reduced. The fluid in the first chamber 1001 ' is discharged into the tank T passing through the check valve lObis, which is driven (opened) by the piston 106, which is in turn driven by a small amount of the fluid directed towards the check valve lObis.

When the rod 1002 is to be moved in the opposite direction, i.e. away from the end cap 100, as shown in Figure 5B, the fluid is delivered by the pump P and the distributor D (which is in the "crossed" position) into the first chamber 1001 ' of the cylinder 1000 passing through the check valve lObis, while the fluid in the second chamber 1001 " is discharged into the tank T passing through the check valve 10 of the present invention, which is driven (opened) by means of the piston 106 so as to allow fluid passage from its second opening 12B to its first opening 12A. In this way, the fluid passing through the second opening 12B out of the second chamber 1001" of the cylinder 1000 is appropriately throttled.

In both the cases described above, the calibrated second opening 12B of the check valve 10, which allows a reduction of the flow rate of the fluid that enters/ exits in/ from the second chamber 1001 " of the cylinder 1000, causes an improvement of the performance of the cylinder 1000 itself, eliminating possible cavitation phenomena without using any additional component.

Finally, as illustrated in Figure 5C, when hydraulic oil is not delivered towards the cylinder 1000, for example when the fluid distributor D external to the cylinder is set in a neutral position, the rod 1002 is held in position by the check valves 10 and lObis, which exert their blocking function.

In the example shown in Figures 5A-5C, only the check valve 10 comprises a calibrated opening, while the check valve lObis is of a known type, only one calibrated opening being usually enough to reduce the cavitation within a cylinder. Moreover, in the example illustrated in Figures 5A-5C, the throttle (i.e. the reduction of the flow rate of the fluid) is implemented at the opening of the valve connected to the second chamber 1001 " (rod-side chamber) of the cylinder 1000.

It is also possible to provide applications wherein both the check valves comprise a calibrated opening, possibly having different calibration values (i.e. different values of the area of the calibrated opening), as well as it is possible to provide applications wherein only one check valve comprises a calibrated opening, but in connection with the first chamber 1001 ' (end cap- side chamber). Moreover, in an alternative embodiment of the present invention (not shown in the figures) the hydraulic cylinder 1000 may also be a single-acting cylinder, i.e. only comprising a single check valve 10 according to the present invention. In this case, the fluid is supplied only into one of the first chamber 1001 ' and the second chamber 1001 " of the cylinder 1000, causing the movement of the rod 1002 only in one direction along the longitudinal axis H'-H'. In this case, the cylinder 1000 comprises suitable pushing means (not shown in the figures) that allow the movement of the rod 1002 also in the direction opposite to the push direction of the fluid. As an example, the pushing means can be a spring that exerts a force opposite with respect to that exerted by the fluid. It is of course possible to provide a piston that drives (opens) the check valve 10 during the action of the pushing means.

In this case, the check valve 10 is called "single-acting pilot operated check valve". It is also possible to provide a double-acting cylinder that only comprises a single-acting pilot operated check valve, for example in case it is desired to control the load connected to the cylinder in only one direction.

In a further alternative embodiment of the present invention (also not shown in the figures), the hydraulic cylinder 1000 can be a plunger cylinder, comprising only the rod 1002 and not the piston 1003, i.e. a cylinder wherein the end of the rod 1002 facing the end cap 100 acts as a piston itself.

It is also observed that, in an embodiment of the present invention not shown in the figures, the hydraulic cylinder may be provided, in addition to the check valve 10 having the calibrated second opening 12B, with a further calibrated throttle implemented on the ducts or pipes connected to such second opening 12B of the check valve 10. For example, the further throttle may be implemented by means of a calibrated hole in which a suitable grub screw is inserted, so as to provide a further and finer flow rate reduction. In conclusion, the present invention provides a check valve wherein at least one opening, for example the outlet opening, is suitably calibrated by reducing the area of the cross-section thereof, such reduction being performed as a function of the working pressure and of the flow rate required for a fluid flowing through said opening. In other words, the calibrated opening forms a throttle that reduces the section of passage of the fluid. In this way, the check valve can be suitably integrated into a component, preferably the end cap, of a hydraulic cylinder which is controlled by such a valve.

Advantageously according to the present invention, the use of a calibrated opening, in particular having a reduced sectional area, allows to reduce the flow rate of a fluid passing through it, so that it can properly adjust the movement of a hydraulic cylinder controlled by the valve.

For example, in the case of double-acting cylinders such as the struts of the three-point hitches of tractors, the reduction of the flow rate of the fluid entering the cylinder (in case of fall of the rod) or exiting the cylinder (in case of rise of the rod) leads to a slow and continuous movement of such cylinder when it must move a specific load.

In particular, this feature of the check valve of the present invention easily eliminates possible cavitation phenomena within the cylinder, such phenomena occurring when the flow rate of the fluid exiting the cylinder is much greater than the one of the fluid entering the cylinder and causing an intermittent operation of the check valves. In extreme cases, these phenomena can lead to the vibration or even the breakage of the valves, making the loads applied to the cylinder unstable. The aforementioned problem is thus advantageously solved by the present invention.

Even more advantageously, such feature allows the reduction of the flow rate of the fluid without the use of further components external to the check valve, such as, for example, throttle valves connected to an opening thereof, thus allowing the easy integration of such check valve within the end cap of the cylinder and thus allowing an unprecedented instrumental compactness.

In this way, it is not necessary to connect the check valves and the throttle valves externally to the cylinder anymore, thus avoiding possible damage or breakage of the valves themselves, as well as avoiding an unauthorized operation thereof by a user, who no longer needs to adjust any throttles.

Furthermore, the present invention reduces the spatial dimensions of the cylinder into which the valves are integrated.

The present solution ensures notable economic savings (only one component is used and breakages of external pipes and / or of the valves are avoided), as well as an increase in the safety of a user who uses the cylinder.

The safety of a user is further ensured also in that the fluid velocity is automatically adjusted by the check valve itself, preventing him from incorrectly adjusting a throttle valve as that used in the known solutions. It should be noted that the calibrated opening of the check valve of the present invention is properly sized according to the particular application thereof, specifically as a function of the optimal flow rate of the fluid passing through such opening.

It is thus possible to provide a hydraulic cylinder having check valves integrated into its end cap, wherein at least one check valve is calibrated in an easy way, by simply reducing the dimensions of an opening thereof as a function of the flow rate required by the fluid flowing therethrough.

Finally, it should be emphasized that the present invention can be applied to a wide range of cylinders in addition to those already mentioned, for example to tool-carrying arms (so-called "parallels") and to stabilizers of a three-point hitch of a tractor, as well as to the front tool-carrying arms of a tractor and to many other applications. Obviously, a person skilled in the art, in order to meet particular needs and specifications, can carry out several changes and modifications to the check valve, to the component, and to the cylinder described above, all included in the protection scope of the invention as defined by the following claims.