PRESSURI ZED FLUI DS

D ESCRI PTI ON

Technical Field of the Invention

The present invention relates to a control and safety system suitable for conveying circuits of fluids under pressure.

In fact, during the operation of such circuits, one of the greatest risks occurs when at least a portion of the process circuit can be in overpressure conditions, with the consequent structural failure of a portion of this circuit and the leakage of the process fluid. For this reason, the present invention aims as a primary objective to verify the circuit and the components used for the implementation of countermeasures designed to avoid the emergence of such problems.

Known Technique

Over time, various safety systems have been developed to prevent the leakage of a process fluid from a pressurized circuit, when an anomalous overpressure occurs that jeopardizes the integrity of the circuit itself.

A first system provides for the opening of an alternative discharge for the process fluid, should the pressure be beyond the safety limits. In such circumstances, the fluid is discharged and removed from the line of the circuit, so avoiding the problems mentioned above but adding complications related to how to treat the exhaust in the process flow.

According to other known systems and methodologies, it is preferred instead to block the fluid in appropriately designed portions of the plant, that is capable of containing high pressures and thus avoiding damage to the other portions of the installation. In such systems, process valves are therefore used which act as a barrier between the areas designed for high pressure and those which are not suitable for containing high pressures. These valves and the accompanying instrumentation used are called HIPPS, an acronym for "High Integrity Pressure Protection System".

Regarding the safety function they must perform, such process valves are kept constantly open in order to allow the continuous flow of the process fluid and are closed should problems of overpressure arise, thus carrying out the emergency maneuver, or exerting the safety function For this reason, amplification devices are often used which are necessary to achieve the safety function in adequate times, normally in the order of a few seconds. However, during the useful life of the system it may be useful to check the correct operation of such process valves by performing a partial closing operation of the valve itself in anticipation of a possible future use. Such operation, typically called "partial stroke test" (hereinafter, also "partial stroke operation"), is clearly more effective if it verifies the correct functioning of the complete valve kit accessories in question, without excluding any portion of the logic circuitry useful to the movement of the valve. It is also evident that by minimizing the execution time of such operation this can lead to both economic and technical advantages, as the process would be altered for a shorter period of time. Moreover, when performing the test with speeds comparable to the hypothetical emergency operation, this is more convincing as it approaches the real emergency conditions.

In order to better understand how the "partial stroke test" is carried out according to the known technique and what are the current limits which the invention proposes to overcome, an accurate explanation is necessary and for this reason reference is made to the attached figure 1 (which then represents the today’s state of the art. As shown in such figure, a system with an on-off single-acting actuator, configured for partial stroke operations, is typically made by:

- a pressure reducer 1 ,

- a solenoid valve 2 ,

- a three-way valve with pneumatic/hydraulic pilot 4,

- a three-way with manual pilot valve 7,

- a three-way mechanical pilot valve 9,

- three control valves 3, 6, 8 ,

- two quick-discharge valves 5, 10, and

- one single-acting on-off actuator 11.

Such system can be divided into two circuits: the first one, the circuit A, which is useful for the normal operation of the actuator, and the second one, the circuit B, which is necessary to carry out the partial stroke operation (partial stroke test ).

Considering the circuit A, in the example shown in figure 1, the lower chamber 12 of the actuator 11 is the chamber to be pressurized in order to open the process valve (not shown in figure 1) on which the actuator single- acting actuator 11 is mounted. Under normal operating conditions of the valve, the latter must be kept fully open, and therefore the lower chamber 12 of the single-acting actuator 11 must be kept under pressure. For this reason the lower chamber 12 is connected to the supply line of the working fluid according to the circuit A. The supply line of the working fluid (indicated in figure 1 as "FLUID SUPPLY") is connected to the solenoid valve 2 and to the control valve 3 through the pressure reducer 1. The solenoid valve 2 controls the pilot of the three-way valve with pneumatic/hydraulic pilot 4 while the control valve 3 regulates its supply. The output of the three-way valve with pneumatic/hydraulic pilot 4 is connected to the rapid discharge valve 5. The latter operates in two ways: either it can put the supply line of the working fluid in communication with the lower chamber 12 of the single-acting actuator 11 (and in such case we speak of a loading action of the actuator), or it can put in communication the lower chamber 12 of the single-acting actuator 11 with the control valve 6 (in the latter case we speak of an unloading action of the actuator). The control valve 6 communicates with the external environment or with a dedicated conveying circuit, so allowing the discharge of the fluid. The state of the quick-discharge valve 5, and therefore the mode with which it acts, is defined by the pressures established upstream of the same quick-discharge valve 5.

By acting on the solenoid valve 2, on the control valve 3 (for regulating the flow rate during the loading phase of the lower chamber 12 of the single- acting actuator 11) and on the control valve 6 (for regulating the flow rate in the exhaust phase of the lower chamber 12 of the single-acting actuator 11), such circuit is therefore able to manage the handling of the single-acting actuator 11 , so allowing the closing or opening of the process valve on which it is mounted. During normal operation conditions, the valve is fully open, therefore the solenoid valve 2 is kept energized (electrical signal SIGNAL) in order to ensure the communication between the working fluid supply line and the lower chamber 12 of the single-acting actuator 11. In emergency conditions, when the fast closing of the process valve is required, the solenoid valve 2 will be de-energized. This will change the state of the quick discharge valve 5 and consequently the lower chamber 12 of the single-acting actuator 11 will be put in communication with the control valve 6.

Considering now the circuit B, in addition to what has been described before, such circuit has further components, which are useful for performing the partial stroke operation. As shown in figure 1, the lower chamber 12 is in fact connected to the upper chamber 13 by means of several components placed in series. More precisely and starting from the lower chamber 12 such components are: the control valve 8, the three-way manual pilot valve 7, the three-way mechanical pilot valve 9 and the quick-discharge valve 10. The latter can put in communication either the upper chamber 13 of the single- acting actuator 11 with the three-way mechanical pilot valve 9, or the upper chamber 13 of the single-acting actuator 11 with the external environment or with a dedicated conveying circuit. The mechanical pilot of the three-way valve 9 is also connected to the kinematic mechanism 11' of the single-acting actuator 11 , such kinematic mechanism then representing the opening degree of the process valve on which the single-acting actuator 11 is mounted.

The usefulness of such circuit is to allow the communication between the lower chamber 12 and the upper chamber 13 of the single-acting actuator 11, in the case in which the valve is in a predetermined stroke range and at a time when there is such request by an operator. In particular, if the valve is located between the total opening and a determined intermediate position, the three-way mechanical pilot valve 9 is de-energized. The intermediate position is defined by the position of the kinematic mechanism 11' of the actuator 11. As in normal operating conditions the valve is completely open, the three-way mechanical pilot valve 9 is therefore de-energized. In such conditions, the only difference in order to create the by-pass between the chambers 12 and 13 and to perform the partial stroke test, is the state of the three-way manual pilot valve 7. If necessary, an operator can therefore energize such three-way valve 7, by starting the partial stroke operation. In fact :

- by energizing the three-way valve manual pilot valve 7 the chambers 12 and 13 of the actuator 11 are put in communication, with a consequent increase of pressure in the upper chamber 13 and the beginning of the valve closing phase. Once the predetermined stroke percentage has been reached, the three-way valve mechanical pilot valve 9 is energized, being driven by the mechanical connection set on the kinematic mechanism 11 ' of the actuator 11. In such conditions the rapid discharge valve 10 is de-energized, making a direct connection of the upper chamber 13 with the external environment or dedicated conveying circuit. The resulting pressure decrease of the upper chamber 13 therefore involves a trend by the single-acting actuator 11 by opening the process valve once again, thanks also to the pushing given by an elastic means, typically a spring 14. In such circumstances the mechanical connection set on the kinematic mechanism 11 ' of the actuator 11 causes a further change of state of the three-way mechanical pilot valve 9, by bringing it back to the de-energized state. The final effect is therefore the modulation of the pressure in the chambers 12 and 13 by means of the three-way mechanical pilot valve 9, by consequently keeping the process valve in the position associated with the intermediate position defined by the kinematic mechanism 11 ' of the actuator 11. Such position relates to the partial stroke operation;

- by subsequently de-energizing the three-way manual pilot valve 7 the supply to the upper chamber 13 is totally excluded, therefore leaving the partial stroke operation. Under normal operating conditions, the circuit A will then supply the lower chamber 12 by bringing the valve back to its fully open state.

From the example described, according to the known art, it is clear that:

- the emergency closing of the process valve (hence the fulfillment of its safety function) is carried out by an actuator and by the respective control circuit (circuit A, in the example illustrated), - however, such circuit is not involved during the partial stroke test as such function is performed by a dedicated test circuit (circuit B) , which can exclusively check the correct operation of the actuator-valve system only.

I n such way the diagnostic coverage of the test is negligible, as it excludes the control circuit of the actuator which is useful for carrying out the em ergency operation.

There is therefore the need to define a new control and safety system which is suitable for conveying circuits of fluids under pressure, which overcom es the described drawbacks.

Sum mary of the I nvention

Main purpose of the present invention is obtained through the definition of a circuit system apt to perform both the partial stroke operation and the em ergency operation. I n this way, the present invention overcom es the lim itations of the prior art, as during the partial stroke operation it perm its to check the entire system made of actuator-valve-circuit process, thus ensuring a total diagnostic coverage which involves all com ponents useful to perform the safety function, in emergency conditions. Furthermore, the control circuit is designed so as to perform the partial stroke operation in less time than that used by the systems according to the prior art, at the same time with tim es analogous to the actual operation, by taking advantage at the same time of the components already used for the actuator em ergency operation and without im plementing dedicated circuits .

These and other obj ects and advantages are achieved, according to the invention, by a control and safety system suitable for pressurized fluid conveying circuits, with the characteristics set forth in the appended independent claim . Further preferred and/or particularly advantageous embodiments of the invention are described according to the characteristics set forth in the appended dependent claims.

Brief Description of the Drawings

The invention will now be described with reference to the annexed drawings, which illustrate a non-limiting embodiment of the same, in which: figure 1 is a circuit diagram of a control and safety system for a pressurized fluid conveying circuit, according to the prior art,

figure 2 is a circuit diagram of a control and safety system for a pressurized fluid conveying circuit, according to an embodiment of the present invention , and

figure 3 is a circuit diagram of a control and safety system for a pressurized fluid conveying circuit, according to an alternative embodiment, without electric control, of the present invention .

Detailed Description

Referring now to figure 2, the control and safety system for a pressurized fluid conveying circuit, according to an implementation of the present invention, is used for performing the partial stroke operation on on- off single-acting actuators. This system 100 comprises :

- a pressure reducer 16 ,

- a control valve 17,

- a secondary valve 18,

- a pressure switch 19,

- a shuttle valve 20 ,

- a flow amplifier valve 21 , and

- a single-acting actuator 22. The system 100 by means of the circuit which will now be described is suitable both to perform the partial stroke operation, and for moving the single-acting actuator 22 under normal operating conditions and in emergency situations (rapid closing of the process valve. Such circuit therefore includes both the functions performed by the circuit A and the circuit B of figure 1, by using the same circuit means for performing both the partial stroke operation and the emergency operation, with superimposed response characteristics. During the partial stroke operation therefore the entire control circuit is involved, so ensuring a complete diagnostic coverage of the system made of actuator-circuit-valve.

The working fluid line is directly connected to the flow amplifier valve 21, to the control solenoid valve 17 and to the pressure reducer 16. Downstream of the latter the secondary solenoid valve 18 is connected. The control solenoid valve 17 and the secondary solenoid valve 18 are both connected to the shuttle valve 20, which manages the delivery of the working fluid to the pilot means of the flow amplifier valve 21. The pressure switch reads the pressure downstream of the secondary solenoid valve 18 and upstream of the shuttle valve 20. The flow amplifier valve 21 is directly connected to the single-acting actuator 22 and has the function of loading or unloading the actuator 22 on the basis of the pressure signal which reaches the pilot.

Let us now consider both the solenoid valves 17 and 18 in their de energized state. In the case where only the control solenoid valve 17 is energized, the supply fluid will drive the flow amplifier valve 21, by going through the shuttle valve 20. As a consequence, the amplified supply of the lower chamber 23 of the single-acting actuator 22, is allowed by the direct connection of the flow amplifier valve 21 to the working fluid line. In such conditions the valve normally operates, with the lower chamber pressurized 23 and the valve totally open. By acting on the secondary solenoid valve 18 it is then possible to perform the partial stroke operation, in particular:

by energizing the secondary solenoid valve 18, the supply fluid reaches the shuttle valve 20 with a pressure equal to the value set by the pressure reducer 16. The pressure switch 19 therefore reads the pressure increase along the line and changes the state of the control solenoid valve 17, which closes the supply to the shuttle valve 20 and starts discharging the residual fluid in the line communicating with such valve 20. The simultaneous effect of pressurizing the line downstream of the secondary solenoid valve 18 and discharging the line downstream of the solenoid control valve 17, is translated into a reduction of the pilot pressure of the flow amplifier valve 21 (and, consequently, in an amplified discharge of the lower chamber 23 of the single- acting actuator 22). This behavior continues until a certain pressure value in the lower chamber 23 of the single-acting actuator 22, as a function of the pressure formed at the pilot of the flow amplifier valve 21, such pressure value being equal to the pressure value set at the pressure reducer 16. This means that for different setting values of the pressure reducer 16 it is possible to define different pressures in the lower chamber 23 of the single- acting actuator 22, and therefore a different location of the same actuator 22 and a different degree of opening of the process valve on which the actuator is mounted . The value of the partial stroke is therefore imposed by setting the pressure reducer 16 ;

by subsequently de-energizing the secondary solenoid valve 18, it closes the supply to the shuttle valve 20 and discharges the residual fluid in the line communicating with such valve 20. The pressure drop along such line therefore involves the change of state of the control solenoid valve 17 through the impulse given by the pressure switch 19. The supply fluid therefore reaches the shuttle valve 20 exclusively from the line related to the control solenoid valve 17, allowing it to pass towards the pilot of the flow amplifier valve 21. As a consequence, the supply of lower chamber 23 of the single- acting actuator 22 is amplified through the flow amplifier valve 21, therefore with the complete opening of the valve.

With reference to figure 3, an alternative embodiment of the control and safety system is now described for a pressurized fluid conveying circuit, according to the present invention.

This system 200 is similar to the system previously described in figure 2, with the difference that in this latter configuration there is no component electrically driven. Such alternative may be of particular interest if there is no possibility to activate the partial stroke test and/or the emergency operation by means of an electrical signal. System 200 includes:

a pressure reducer 16,

a three-way pilot valve 24,

a three-way control valve 25,

a three-way secondary manual pilot valve 26,

a shuttle valve 20,

a flow amplifier valve 21 , and

a single-acting actuator 22.

In particular, with respect to system 100 of figure 2, in system 200: the control solenoid valve 17 is replaced by the three-way control valve

25 ,

the secondary solenoid valve 18 is replaced by the secondary three-way manual pilot valve 26, the pressure switch 19 is replaced by the three-way pilot valve 2 4.

The working fluid line is directly connected to the pressure reducer 16, to the flow amplifier valve 21, to the three-way control valve 25 and to the three-way pilot valve 24. Downstream of the pressure reducer 16 the three- way secondary manual pilot valve 26 is connected. Downstream of the three- way pilot valve 24 the three-way control valve 25 is connected. Both the three-way secondary manual pilot valve 26 and the three-way control valve 25 are connected to the shuttle valve 20, which manages the delivery of working fluid to the pilot of the flow amplifier valve 21. The pilot of the three- way pilot valve 24 is further connected downstream of the three-way secondary manual pilot valve 26 and upstream of the shuttle valve 20. The flow amplifier valve 21 is directly connected to the single-acting actuator 22 and has the function of loading or unloading the actuator 22 according to the pressure signal that reaches the pilot.

The operation of system 200 is described below. Let us consider the three-way secondary manual pilot valve 26 in its de-energized state. In such conditions the three-way pilot valve 24 is de-energized and therefore allows the passage of the working fluid towards the pilot of the three-way control valve 25. The supply fluid will drive the flow-amplifier valve 21, by going from the three-way control valve 25 and the shuttle valve 20. As a consequence, the supply of the lower chamber 23 of the single-acting actuator 22 is increased, which is permitted by the direct connection of the flow amplifier valve 21 with the working fluid line. In such conditions the valve normally operates, with the lower chamber pressurized 23 and the valve totally open. Such condition is similar to the operation described for the circuit of figure 2, when only the control solenoid valve 17 is energized. By acting instead on the three-way secondary manual pilot valve 26, it is possible to perform the partial stroke operation. In particular:

by energizing the three-way secondary manual pilot valve 26 the supply fluid will drive the three-way pilot valve 24, which discharges the residual fluid to the pilot of the three-way control valve 25. The three-way control valve 25 is thus de-energized, thus releasing the residual fluid between the three-way control valve 25 and the pilot of the shuttle valve 20. As previously described regarding system 100 of fig. 2, the simultaneous effect of the three-way secondary manual pilot valve 26 and the three-way control valve 25 results in an amplified discharge of the lower chamber 23 of the single-acting actuator 22. In particular, for different setting values of the pressure reducer 16 it is possible to define different pressures in the lower chamber 23 of the single- acting actuator 22, therefore a different position of the same actuator 22 and a different degree of opening of the valve on which the single-acting actuator 22 is mounted. The value of the partial stroke, as well as for the implementation of figure 2, is therefore imposed by setting the reducer 16;

by subsequently de-energizing the three-way secondary manual pilot valve 26, it closes the supply to the shuttle valve 20 and starts discharging the residual fluid in the line communicating with the same shuttle valve 20. The three-way pilot valve 24 changes its state and allows again the passage of the working fluid towards the pilot of the three-way control valve 25. The supply fluid therefore reaches the shuttle valve 20 exclusively from the line related to the three-way control valve 25, by allowing its passage towards the pilot of the flow amplifier valve 21. As a consequence, the supply of the lower chamber 23 of the single-acting actuator 22 is increased through the flow amplifier 21 , thus with the complete opening of the valve. In addition to the embodiments of the invention, as described above, it is to be understood that numerous further variants exist. It must also be understood that these implementation modes are only exemplary and do not limit neither the subject of the invention, nor its applications, nor its possible configurations. On the contrary, although the above description makes it possible for the professional man to carry out the present invention at least according to one of its exemplary configurations, it is to be understood that many variations of the described components are conceivable, without thereby departing from the subject of the invention, as defined in the attached claims, literally interpreted and/or according to their legal equivalents.