VALVE

DESCRIPTION

Technical field of the invention

The present invention relates to a system and a respective method for diagnosing leaks between the seat and the shutter of a valve, with reference to the unavoidable leakage existing between the two components. In particular, the system and the method according to the present invention also allow the predictive analysis of the leakage of a valve.

Background art

As is known, the leakage is an internal loss to a valve that originates from the interface between seat and shutter. In particular, when a valve is closed there is a perfect seal, i.e., the flow rate of the process fluid between the seat and the shutter valve is equal to zero. In reality, a leak is always existing and the valves are classified according to the maximum acceptable leakage in the closed valve condition. This leakage is divided into classes according to norm ANSI B16.104. The extent of the leakage depends on a multiplicity of parameters such as, for example, the design of the valve, the materials that make up the seat/shutter assembly, the quality of the surfaces, the force with which the shutter is pressed onto the seat, a force that is typically provided by an actuator mounted on the valve. In addition, during the useful life of a valve, then even in the case of specific interest of a control valve, the leakage of the process fluid may increase over time. The increase in leakage is due to many factors, for example, the progressive degradation of the shutter and the seat following phenomena of cavitation, wear, deformation, presence of particulate matter in the process fluid, etc. The increase in leakage can thus entail the loss of efficiency of a plant, and consequently, economic losses, security issues (e.g., in the event of leakage of toxic and/or flammable fluids), as well as greater degradation of the seat and shutter.

According to the known art, maintenance interventions are carried out only following the malfunctioning of the system, for example when there is a marked loss of efficiency of the plant due to the leakage of a valve. In these cases, when the loss due to a leakage becomes detectable, already important leaks exist which are not predictable enough in advance.

Furthermore, still according to the known art, it is common to generate on the closed valve the maximum force that can be achieved by the actuator, or in any case a high and constant force value, for a greater tightening of the valve seat and the shutter. This procedure, if made on one hand at the beginning of the valves operating life, avoids situations of incipient leakage, and on the other hand it creates a contact pressure between the seat and the shutter that stresses the mechanical resistance of the components more than necessary, causing premature wear of the two components themselves.

However, systems and related methods are not known to the state of the art, which allow to carry out a diagnostic in real time, as well as a predictive diagnostic of the losses due to leakage of a valve, i.e., in order to be able to calculate in advance the operating trend over the time of the losses due to leakage of the valve, in order to intervene promptly with appropriate maintenance. In this way, it would also be possible not to oversize the force delivered by the actuator and therefore with a lower stressing of the seat and shutter of the valve.

There is therefore a need to define a system and a relative method for real-time and predictive diagnostics of losses due to leakage between seat and shutter of a valve that allows to achieve the advantages cited above.

Summary of the invention Subject of the present invention is therefore a system applied to a valve for the execution of a real-time and predictive diagnostics of losses due to leakage of the valve, comprising an actuator, a positioner mounted on the actuator, at least one sensor mounted on the valve and a controller. The valve, which can be of any type, comprises, as is known, a shutter and a sealing seat and is not part of the present invention, but represents its natural application.

The actuator determines with the force generated the position of the valve shutter and, in closed valve conditions, the force exerted by the valve shutter on its seat. The actuator, by way of example, can be double-acting (with a balance between two pressure chambers) as in the embodiment of the invention presented below. With the appropriate considerations on pressures and forces, this description can also be extended to a single-acting actuator (with a balance between a force linked to a pressure in a chamber and a resisting force, for example an elastic force).

The positioner, as also known, is a component which, connected to the actuator through a mechanical feedback of the position, is able to vary the pressure in the actuator chambers, in order to position the valve shutter where required. In the case of a closed valve, therefore in the case in which the shutter is in contact with the seat, the positioner can modulate the contact force seat/shutter by varying the pressure in the chambers.

A first sensor, which is a normal feedback sensor according to the known art, is capable of detecting the extent of the leakage directly or indirectly by means of a quantity dependent on the leakage of the valve seat itself. This size may vary according to the type of sensor used.

The controller, through the use of a software that implements a suitable control algorithm, correlates the data provided by the sensor with those provided by the positioner, that is, respectively, the quantity measured on the valve (as a function of the valve seat seal) and the contact force seat/shutter normally derived from one or more the pressures in the actuator chambers. In other words, it is therefore possible to relate the degree of tightness or leakage of the valve seat to the force exerted by the actuator on the seat itself. Advantageously, the controller can be integrated in the positioner itself. Advantageously, the seat/shutter pair is not stressed unnecessarily, but the force is limited to that generated by the positioner and is sufficient to guarantee the seal, i.e., an acceptable leakage threshold, therefore the seat/shutter pair is subjected to less stress in the span of its operational life, probably resulting in an extension of the operational life itself.

Advantageously, with the valve closed, as the actuator generates a force which is lower than its maximum capacity, it is possible to open the valve in a shorter time, i.e., with times shorter than those required according to the prior art, as there is a benefit of a lower dead time (the time required for detachment between shutter and seat).

Therefore, an object of the present invention is a system applied to a valve for the execution of a real-time diagnostic and prediction of losses due to leakage of the valve itself, as specified in the attached independent claim of the system.

According to another object, the present invention also consists of a method for carrying out the predictive diagnostics of the leakage losses of a valve, as specified in the attached independent claim of the method.

The dependent claims outline particular and further advantageous aspects of the invention. Brief description of the drawings

These and other advantages of the invention will now be described in detail, with reference to attached Figures, which represent an exemplary embodiment of the invention, in which: Figure 1 shows a diagram of the system object of the present invention;

- Figure 2 is a graph relating to the 'trend over time of the force F _act exerted by the actuator to ensure the seal between the shutter and valve seat, during normal operation, compared to a reference force F _set necessary to ensure an optimal seal of a valve and its tolerance range;

- Figure 3 is a graph equal to that of Figure 2 and also shows a future projection of values of the actuator force Fact, even outside of the tolerance range considered;

- Figure 4 shows a graph over time of the seal test in order to obtain a correlation between the parameter measured by the sensor and the actuator force F _act .

Detailed description

With reference to attached Figure 1 ANNEX, according to an absolutely non-limiting embodiment of the present invention, a system 100 applied to a valve 1 is shown, of the known type and comprising a shutter and a sealing seat. The system 100 includes an actuator 2, a positioner 3, at least one sensor 4 and a controller 5 provided with an analysis software. The controller 5 can be a "stand alone" component, as well as it can be integrated into the positioner 3. The actuator 2, by way of example and in a non-limiting way, is double-acting. As is known, this means that the control stem of the actuator, the organ which applies a force to the valve shutter, is immersed between two chambers in which the relative pressures are balanced and a net force acts on the control stem, which is transmitted to the valve shutter. Of course, with appropriate considerations on pressures and forces, the invention can also be implemented with a single-action actuator, having a single pressure chamber and where the balance of the forces occurs between a force linked to the pressure in the pressure chamber and a resisting force, for example an elastic force.

The positioner 3 is a component which determines the "behavior" of the actuator 2 as it regulates the pressure acting in the pressure chambers of the actuator 2 itself. The logical connection with the actuator 2 is made by means of mechanical feedback of the position of the actuator itself. Based on the feedback on the position of the actuator 2, the positioner 3 is able to vary the pressure in the chambers of the actuator 2 in order to position the valve shutter 1 where required. In the case in which the valve 1 is closed, therefore in the case in which the shutter is in contact with the seat, the positioner 3 can modulate the contact force of the seat/shutter by varying the pressure in the chambers of the actuator 2. The positioner 3 is, therefore, a positioner of the latest generation, the so-called "smart" one, which is able to read the values of the position of the shutter and of the pressure acting on the seat seal, in order to derive the value of the force exerted by the actuator 2.

A first sensor 4 is a normal feedback sensor capable of detecting the extent of the leakage directly or indirectly by means of a quantity dependent on the leakage of the seat of the valve 1 itself. This size may vary according to the type of sensor used.

The sensors used can be, purely by way of a non-limiting example, a temperature detector (for example, an infrared thermometer), a flow detector (for example, a flow meter), an acoustic detector (for example, an ultrasonic microphone) or a combination of them.

The modulation of the seat/shutter contact force by varying the pressure in the chambers of the actuator 2 is achieved through the controller 5 which implements a control in closed loop (leakage -> pressure -> force -> leakage), wherein the controlled variable is the loss due to leakage through the valve seat, which is directly or indirectly derived from the first sensor 4 and the controlling variable is the pressure acting in one or both of the pressure chambers of the actuator 2. In other words, the controller

5 (or directly the positioner 3, if it integrates the controller 5) is able to relate the seat/shutter force of the valve 1 and the degree of leakage of the valve 1 over time.

The availability of such data therefore allows to obtain:

- an immediate value which can be easily compared with the design values: the value of the force necessary for the seat/shutter contact (with such value it is therefore possible to immediately check whether the valve 1 is operating within the design limits);

- a value deriving by historical analysis (relationship between force and leakage over time), namely the degradation curve of the seat/shutter sealing, which allows then a predictive diagnostic through extrapolation of the curve itself.

Furthermore, when working in a closed loop (leakage -> pressure -> force -> leakage), it is possible to adjust the positioner 3 in order to generate the only force necessary to obtain the desired seal between the seat and the shutter, plus a desired margin.

Advantageously, therefore, according to the disclosed method, the seat/shutter pair is subjected to less stress during its operating life. This result is obtained due to the fact that the applied force is equal to that generated by the positioner (i.e., the only force required plus a freely configurable safety margin).

Advantageously, the fact that when the valve is closed the actuator generates a force lower than its maximum capacity, allows the valve to be opened in a shorter time and with less dead times.

When such system is used various tests can be carried out. Those considered to be of greater importance for the investigation of the seal on the valve seat are:

- the on-line test: for any valve the reference force F _set is known, which is useful to ensure a tight seal). During the normal operation of the valve 1, whenever it reaches the closed position, it is possible to record the force F _act exerted by the actuator 2 in order to ensure the tightness of the seat. As shown in Figure 2, the data supplied by the positioner 3 can be collected in a graph. In particular, the controller 5, by means of the analysis software, can deduct from a historical analysis (by comparing the force and the leakage over time) the degradation curve of the seat/shutter seal, so allowing a predictive diagnostic by means of extrapolation of the curve itself.

In this way it is possible to obtain, as shown in Figure 3, a graphical projection of future values of F _act outside of the tolerance range considered. The sensor 4 can also be used to define the tolerance range of the F _set force, as it can be useful as an acknowledgment and verification of the leakage on the seat during the evaluation of the allowable limit forces UCL (upper control limit) and LCL (lower control limit), which are shown both in Figure 2 and in Figure 3. Obviously, the lower limit value LCL is the value below which the valve does not hold, that is its leakage becomes sensible; the UCL limit value is that above which the mechanical resistance of the components in contact (shutter and seat) is put at risk;

- the tightness test: in some systems the valves must work to close for most of the time. It is therefore difficult to perform tests during their useful life and analyze the degree of sealing of the seat over time. In this regard, the system 100 object of the present invention can be used to carry out periodic tightness tests.

During the normal operation of the valve 1, through a control signal to the positioner 3, it is possible to vary the force F _act of the actuator 2 until the appearance of a leakage of the valve seat 1, thereby effecting in such circumstances multiple measurements by means of a second sensor, suitable for measuring a force, for example a load cell (not shown in the Figure). The recording of the data obtained by the second sensor and by the positioner 3 is carried out by the controller 5 by means of the analysis software. At the end of this phase, the initial value of the force F _act is restored in order to guarantee again the optimal seal on the seat (the leakage of the working fluid generated during the test is used exclusively for data collection and although it does not compromise the closing function of the valve itself, it can lead to alteration of the state of the system: it is therefore necessary to carry out such test with due precautions, depending on the type of valve investigated).

As shown in Figure 4, the succession of tightness tests over time leads to obtaining a relationship between the parameter measured by the sensor 4 and the force F _act of the actuator 2, by identifying a tolerance range of such parameter within which the seal of the valve seat 1 is considered acceptable (the tolerance range in addition to that associated with F _act is therefore obtained as a reference) .

Ultimately, due to the system 100 and the associated method, it will always be possible to identify the minimum value of the force necessary to guarantee an absence of perceptible leakage. In this way, excessive force values will not be used and consequently the valve, being subjected to less wear, will have a longer useful life. Advantageously, the integrated system 100 can be designed in more complex configurations, capable of recording multiple quantities through the use of a plurality of sensors. In this way, it is therefore possible to increase the diagnostic level of the integrated system and to predict the valve seat seal trend with more precision. When one of the measured quantities will tend to go out of the respective tolerance range defined during the test, it will therefore be necessary to intervene with preventive maintenance actions.

Such tests can be useful for different purposes, such as the control of a valve assembly through a statistical analysis of the data collected on a plant or on multiple plants. Furthermore, the remote monitoring of such data can be useful to generate a database concerning the useful life of the investigated valves.

While at least one exemplary embodiment has been presented in the summary and the detailed description, it is to be understood that there are a large number of variants within the scope of the invention. Furthermore, it must be understood that the one or more presented embodiments are only examples which are not intended to limit in any way the scope of protection of the invention or its application or configurations. Rather, the brief and detailed description provides the technician skilled in the art with a convenient guide for implementing at least one exemplary embodiment, being it clear that numerous variations can be made in the function and assembly of the elements described herein, without departing from the scope of protection of the invention, as established by the attached claims and by their technical-legal equivalents.