CALIBRATION METHOD FOR A PRESSURE LIMITING VALVE.

Abstract

A method for calibrating a valve (1), wherein a valve seat (6) houses a movable element (7), a spring (9), and a sphere (8) carried by the movable element (7) and configured to rest on a support seat or buttress (10) housed in the valve seat (6) and provided with a channel (11) communicating with a valve inlet (22). The method comprises a calibration cycle in which the following steps are performed: axially moving a thrust element (30) to displace the support element (10) along the axis that compresses the spring; supplying pressurized fluid at the valve inlet (22); creating a constriction at the valve outlet; and maintaining the pressure inside a chamber containing the sphere so that said pressure is close to a preset value in order to obtain a controlled opening of the valve. Figure 1.

Description

PRESSURE LIMITING VALVE CALIBRATION METHOD CROSS-REFERENCE WITH RELATED APPLICATIONS This patent application claims priority over Italian patent application no. 102020000004444 filed on 03 / 03 / 2020, which is incorporated herein by reference. FIELD OF INVENTION The present invention relates to a method for calibrating a pressure limiting valve. BACKGROUND OF THE INVENTION Figure 3 illustrates, according to the prior art, a calibration method for a known pressure relief valve (1) (hereafter also referred to as valve (1)). In particular, the main components of valve (1) will be described in order to illustrate the usual calibration method. Specifically, the valve (1) comprises a valve body (2), provided with a central bore (3) extending along a shaft (4). The central bore (3) defines, at a first end, an opening (5) and at a second end, a valve seat (6); furthermore, the valve seat (6) houses a 52 / 1800 / 22 movable element (7), comprising an elongated portion coaxial with the shaft (4) (needle) and provided at an elongated end thereof, opposite the opening (5), with a concavity adapted to contain a sphere or ball (8) (e.g., made of steel). The valve seat (6) also houses a spring (9), arranged coaxially with the shaft (4) and provided with a first end, arranged in contact with a lower wall of the valve seat (6), and a second end, arranged in contact with the elongated portion of the movable element (7). The valve (1) also comprises a cylindrical support seat (10), which is arranged in the central hole (3) and has a central portion that defines a channel (11) coaxial with the shaft (4). In particular, according to known methods, the cylindrical seat (10) is implanted at a predetermined height within the central hole (3), so that the spring (9) acquires a predetermined compression value and pushes the ball or sphere (8) against the cylindrical support seat (10), closing the channel (11) with a thrust force F equal to a calibration value Ft. This operation is carried out by means of a calibration tool (12), which is provided with a punch (13) that penetrates the opening (5) and rests on the cylindrical support seat (10), displacing it axially. 52 / 1800 / 22 In this way, the spring (9) is compressed by the effect of a thrust force Fs, applied by the cylindrical support seat (10) until it reaches a height such that the force F corresponds to the calibration force value Ft set as the target, so that the valve (1) opens. In order to control the value of the calibration force Ft, it has to be measured directly; usually, the measurement is made using a point (14a), mounted coaxially on the punch (13), which exerts pressure on the sphere (8). However, in known control methods, not all boundary conditions are considered; that is, the variables that intervene between the spring's calibration force (Ft) and the actual opening pressure, such as the tolerance in the seal seat angle and the surface finishes of the sealing surfaces. This variability prevents achieving sufficient tolerance in the actual opening pressure, since a percentage of the calibration force (Ft) is reserved for the uncertainty regarding the boundary conditions. Alternatively, the opening pressure can be measured directly by supplying the valve with a pressurized fluid. In that case, the measurement of force is also ML / t / ZUZÓ / UU4y / z 52 / 1800 / 22 is crucial because the valve's dynamics are significantly affected by the flow rate of the fluid passing through it; moreover, the fluid flow rate cannot be determined by a simple fixed orifice, as the flow rate depends on the opening pressure. An orifice designed to generate a flow rate relative to the target opening pressure will produce a much higher flow rate in the initial pressure measurements, before the valve has been calibrated. Flow rates exceeding a certain limit cause uncontrolled dynamics in the valve, making accurate static measurement of the opening pressure impossible and resulting in stress on its components. In fact, uncontrolled opening and closing occur, and the internal sphere begins to bounce and strike the seat, causing damage. In summary, there are no reliable methods in the state of the art to perform valve calibration under stable conditions. SUMMARY OF THE INVENTION The technical problem then is to calibrate the valve using the direct method, that is, by supplying the fluid under pressure and ensuring a stable process that allows the valve to open under equilibrium conditions, in order to 52 / 1800 / 22 guarantee high precision, accuracy and reproducibility when reaching the preset opening pressure and thus preserve the integrity of the valve. According to the present invention, a method for calibrating a valve is provided, as stated in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS In order to better understand the present invention, a preferred embodiment thereof will now be described by means of a non-limiting example, with reference to the accompanying drawings, where: - Figure 1 shows a cross-section of a pressure limiting valve subject to the method of the present invention; - Figures 2-1 to 2-III show a flowchart of the present calibration method; - Figure 3 illustrates the prior technique; and Figure 4 illustrates a variant of the method according to the present invention. BEST WAY TO CARRY OUT THE INVENTION Figures 2-1 to 2-III schematically show the present calibration method applied to the valve (1) of Figure 1. In particular, the method has 52 / 1800 / 22 as a basis an iterative and adaptive algorithm, in which it is possible to optimize the number of steps needed to complete the calibration of the valve (1). Specifically, the pressure limiting valve 1, schematically illustrated in Figure 1, comprises a valve body (2) provided with a central cylindrical bore (3) extending along a shaft (4). The central cylindrical bore (3) defines, at a first end, an opening (5) and, at a second end, a valve seat (6). In particular, the valve seat (6) houses a movable element (7) comprising an elongated portion (7a) (needle) coaxial with the shaft (4) and arranged at an elongated end (7b) transverse to the shaft (4) and facing the opening (5), with a concavity adapted to contain a ball or sphere (8) (e.g., made of steel). The valve seat (6) also houses a spring (9), arranged coaxially with the shaft (4) and provided with a first end, arranged in contact with a lower wall of the valve seat (6), and with a second end arranged in contact with the elongated portion (7b) of the moving element (7). The valve (1) also comprises a cylindrical support seat (10), which is disposed in the central bore (3). The cylindrical support seat (10) has MA / t / ZUZÓ / UU4y / z 52 / 1800 / 22 a central portion that defines a channel (11) coaxial with the axis (4) and that communicates at a first end of the same with an inlet (22) of the valve (1). During operation, in the closed position (Figure 1) of the valve, the sphere (8) abuts the seat (10) and closes off a second end of the channel (11). The spring (9) exerts an elastic force that, in the aforementioned closed condition of the valve, keeps the sphere (8) pressed against the cylindrical seat (10), thus closing off the second end of the channel (11). The force exerted by the spring (9) depends on the position of the cylindrical support seat (10) along the axis (4) within the bore (3). As the distance between the seat (10) and the lower wall of the valve seat (6) decreases, the spring is compressed further, and the force increases according to the well-known relationship F = k*x. When the pressure of the fluid supplied from the inlet (22) of the valve to the channel (11) exceeds a limit value, a force is applied to the sphere (8), this force exceeds that exerted by the spring (9) which is compressed; in this way, the sphere (8) moves away from the valve seat (10) and creates an annular space (not represented in Figure 1) for the passage of the pressurized fluid that flows through the valve (1). The sphere (8) separates the channel (11) from a chamber (20) 52 / 1800 / 22 which houses the spring (9), the moving element (7) and the ball (8). The chamber (20) communicates with an outlet (23) of the valve and as illustrated above, the channel (11) communicates with an inlet (22) of the valve. To carry out the calibration operations according to the present invention, the valve outlet (23) is connected to a restrictor device (40) (of the known type) that produces resistance to the discharge of the fluid exiting the outlet (23). Furthermore, a sensor (24) is used to measure the pressure in the chamber (20). A servo-controlled calibration tool (25) is used, i.e., provided with a thrust element (30), movable along the axis (4) by means of motor means (of known type, not represented), which are controlled by an electronic control unit (35) that works according to the instructions in Figures 2-1 to 2-III and that communicates with the sensor (24). At the start of the calibration process (Figure 1 illustrates the initial position of the present valve (1)), the calibration tool (25) is placed above the valve (1) with the pusher element (30) stationary; the cylindrical support seat (10) is housed in the valve seat (6) and is spaced relative to the sphere (8). The elongated portion of the moving element (7) is MA / t / ZUZÓ / UU+y / z 52 / 1800 / 22 placed on the spring (9), which is in the rest position. Alternatively, the cylindrical support seat (10) can be pre-installed at a height such as to load the spring (9) at an intermediate level and lock the sphere (8) between the cylindrical support seat (10) and the moving element (7). With reference to Figures 2-1 to 2-III, which illustrate the operations performed by the electronic control unit (15) operating according to the present method, a calibration cycle is carried out. In this cycle, an initial block (20) is provided that displaces the pusher element (30) from its initial position. Specifically, the pusher element (30) moves axially downwards and advances a predetermined distance (block 30) towards the bottom of the valve seat (6) to reach a predetermined height. The pusher element (30) rests on the cylindrical support seat (10) (block 30) and moves it a predetermined distance until the support seat (10) is adjacent to the sphere (8), which is positioned in the valve closing position, closing the second end of the channel (11).In Figure 1, the thrust element (30) is a T-shaped element provided with a channel for supplying pressurized fluid through the valve inlet (22). 52 / 1800 / 22 supply a gas or a liquid. The pusher element (30) thus has the function of moving the seat (10) and supplying pressurized fluid to the inlet (22) of the valve. The movement of the pusher element (30) ends. In this position, it is necessary to verify that the cylindrical support seat (10) has sufficient interference with the orifice (5) to ensure that, upon removal of the thrust exerted by the T-shaped element, it remains locked in position. For this purpose, it is verified that the force applied by the pusher element (30) is above a preset limit (Minimum Contact Force Check block, block 35). When the check of block (35) produces a negative result, an error is indicated (block 37) and the procedure ends. After the operations described in blocks (30) and (35), the pressurized fluid supply is activated (block 50) with a preset opening value of a valve V6 (Figure 1) that supplies pressurized fluid to the inlet (22) of the valve (1) in order to obtain the separation of the sphere (8) from the seat (10) with respect to the closed position, the displacement of the moving element (7) against the action of the spring (9) and thus the opening of the valve (1). Generally, the fluid pressure has a ramp-up (block 70). ML / t / ZUZÓ / UU4y / z 52 / 1800 / 22 Thus, the sphere (8) begins to move and the pressurized fluid is supplied to the chamber (20). As soon as the generation of a back pressure in the chamber (20) (block 80) is detected, caused by the fluid supplied to the inlet of the valve under calibration (the back pressure is obtained by narrowing the outlet (23) of the valve by means of the constriction (40), thus limiting the fluid outlet), a first adjustment step is activated. In the first adjustment step (blocks 90 and 95) a control cycle is performed on the back pressure detected by the transducer (24), which acts on the degree of opening of the V6 valve to maintain the pressure in the chamber equal to a target value Pquti (for example, 1 bar). During the adjustment step, the valve's supply pressure Pmeasured (block 100) is acquired. This pressure is compared to a set target pressure for the valve Ptarget, calculating the pressure difference ΔP (block 110). Subsequently, the displacement ΔX to be applied to the seat (10) is calculated to reduce the pressure difference ΔP (block 120) to a minimum value. With this calculation, the first adjustment step (block 130) is completed, and the displacement of the thrust element (30) is carried out to physically perform the ΔX movement of the seat (10) (block 140). This concludes the first phase of open-loop calibration. 52 / 1800 / 22 Then, (second phase of closed-loop calibration) the pressurized fluid is supplied again to the valve inlet (block 200 valve opening V6) until (block 210) in the chamber (20) there is a pressure caused by the fluid supplied to the inlet of the valve subject to calibration and which is not completely discharged into the chamber (20) thanks to the narrowing device (40). After a positive check in block (210), another control cycle (blocks 220 and 230) is executed with feedback from valve V6 in order to maintain the pressure in chamber (20) equal to the target value Pquti (e.g., 1 bar). Thus, another adjustment step begins. In this new adjustment step: The supply pressure Pmeasured from the valve (block 240) is acquired, the pusher (30) moves continuously displacing the support seat (10); The measured pressure Pmeasured is compared (block 250) with the target pressure set for the valve Ptarget and when the measured pressure is equal to or greater than the target, the calibration phase ends (block 260 controls the stop of the pusher (30) and block (270) controls the arrangement of the pusher (30) in a rest position). Conversely, when the measured pressure (Pmeasured) is below the target or preset value, the phase of 52 / 1800 / 22 calibration continues (block 280) with the pusher advancing continuously at low speed until the block (250) condition is satisfied. The advantages of the present invention are those inherent in direct calibration, namely, the ability to calibrate the valve during the process by progressively displacing the support seat (10), which causes the reaction spring (9) to be loaded, and to directly read the valve's opening pressure, i.e., the pressure characteristic of the valve. The ability of this method to produce and maintain a stable equilibrium condition with the valve open allows the opening pressure to be measured in equilibrium. In this way, it is possible to calibrate the valve continuously and not by subsequent approximations. Another advantage is the elimination of the violent knocking that occurs between the sphere and the support seat when the valve is opened, since it is possible to prevent the instability of the sphere, typical in this type of valve, thanks to the pressure present in the chamber (20). The method described above allows direct calibration (by controlling the opening pressure and not the spring force) of the valve that is being opened. The method of the present invention is also applicable in the alternative configuration of the MA / t / ZUZÓ / UU4y ! ¿ 52 / 1800 / 22 Figure 4 where the channel (11) is made in the valve body (2) with the sphere (8) arranged adjacent to an end portion of the channel (11), the support seat (10) is devoid of the channel (11) and is arranged on the opposite side of the moving element (7) with respect to what is represented in Figure 1, i.e., adjacent to an end portion of the spring (9). The channel inlet (11) also constitutes the valve inlet. In this case, the thrust element (30) presses on the support seat (10), implanting it within the valve seat (6) and compressing the spring on an opposite side with respect to that illustrated in Figure 1. The outlet of the chamber (20) consists of a channel (50) that extends radially from the chamber (20) and communicates with the narrowing (40). This type of valve configuration cannot be calibrated using the indirect method of calibrating spring preload force, as it is not accessible.

Claims

1. A method for calibrating a valve (1), wherein a valve seat (6) houses a movable element (7) extending along a shaft (4), a spring (9) associated with the movable element (7), and a ball or sphere (8) carried by the movable element (7) and disposed during use, in a closed position, adjacent to a support seat (10) housed in the valve seat (6) and provided with a channel (11) having a first end configured to be closed by the ball or sphere and a second end communicating with an inlet (22) of the valve; the sphere (8) separates the channel from a chamber (20) housing the spring (9), the movable element (7), and the sphere and communicating with an outlet (23) of the valve;The method uses a calibration tool (12) provided with a movable thrust element (30) along said axis (4). The method comprises a calibration phase in which the following steps are carried out: - axially moving the thrust element (30) so that the thrust element (30) rests on the support seat (10) and displaces it with respect to the valve seat (6) and subsequently stops the movement of the thrust element (30); - supplying pressurized fluid to the inlet (22) of the valve being calibrated; - creating a constriction (40) at the outlet (23) of the valve and measuring the pressure inside the chamber (20) by detecting a pressure caused by the fluid supplied to the inlet of the valve being calibrated;Perform an adjustment step for the flow of fluid entering the valve, where the pressure inside said chamber (20) is controlled so that it is close to a set value; acquire the supply pressure (Pmís) of the valve (100) during the adjustment step; compare the pressure (PmiS) with a set target pressure for the valve (Ptarget) by calculating the pressure difference ΔP (110); and calculate the displacement (ΔX) to be applied to the seat (10) in order to reduce the pressure difference (ΔP) to a minimum value (120); control the displacement of the thrust element (30) to physically perform the displacement (ΔX) of the seat (10) ending the adjustment step (140).

2. The method according to claim 1, wherein the step of supplying pressurized fluid to the inlet (22) of the valve subject to calibration comprises step 52 / 1800 / 22 of opening a fluid supply valve (V6) communicating with said inlet (22) such that said fluid supply valve (V6) has a preset opening value; said pressure adjustment step within the chamber comprises the step of acting on the degree of opening of the fluid supply valve (V6) in order to maintain the pressure in the chamber equal to the preset value.

3. The method according to claim 1 or 2, wherein, after said open-loop calibration phase, another closed-loop calibration phase is carried out.

4. The method according to claim 3, wherein in the other closed-loop calibration phase, pressurized fluid is again supplied to the valve inlet (200) until the pressure present in the chamber (20) reaches the preset value; this other adjustment step comprises: acquiring the supply pressure (Pmeasured) of the valve (240); continuously controlling the movement of the pusher (30) to modify the position of the support seat (10) relative to the valve seat (6); comparing (250) the pressure (Pmeasured) with the target pressure set for the valve (Ptarget) and terminating the valve calibration when the measured pressure is equal to or greater than the target; continuing the calibration phase when the measured pressure (Pmeasured) is below the target by continuously advancing the pusher at low speed until the comparison yields a positive result.

5. A method for calibrating a valve (1), wherein a valve seat (6) houses a movable element (7) extending along a shaft (4), a spring (9) associated with the movable element (7), and a ball or sphere (8) carried by the movable element (7) and disposed, in use, in a closed position, adjacent to a first end of a channel having a second end communicating with an inlet (22) of the valve; the sphere (8) separates the channel from a chamber (20) housing the spring (9), the movable element (7), and the sphere and communicating with an outlet (23) of the valve;The method uses a calibration tool (12) provided with a movable thrust element (30) along said axis (4). The method comprises a calibration phase in which the following steps are carried out: - axially moving the thrust element (30) so that the thrust element (30) rests on the support seat (10) housed in the valve seat (6) and displacing it with respect to the valve seat (6) by compressing the spring (9) and subsequently stopping the movement of the thrust element (30); - supplying pressurized fluid to the inlet (22) of the valve being calibrated; - generating a constriction (40) at the outlet (23) of the valve and measuring the pressure inside the chamber (20) by detecting a pressure caused by the fluid supplied to the inlet of the valve being calibrated;To carry out an adjustment step for the flow of fluid entering the valve, where the pressure inside the chamber (20) is controlled to close at a preset value; to acquire the supply pressure (Pmis) of the valve (100) during the adjustment step; to compare (110) the pressure (Pmis) with a set target pressure for the valve (Ptarget) by calculating the pressure difference (ΔP); and to calculate the displacement (ΔX) to be applied to the seat (10) in order to reduce the pressure difference (ΔP) to a minimum value (120); to control the displacement of the thrust element (30) to physically perform the displacement (ΔX) of the seat (10) (140) thus ending the adjustment step. ML / t / ZUZÓ / UU4y ! ¿ 52 / 1800 / 22; 6. The method according to claim 5, wherein the step of supplying pressurized fluid to the inlet (22) of the valve subject to calibration comprises the step of opening a fluid supply valve (V6) communicating with said inlet (22) such that said fluid supply valve (V6) has a preset opening value; said step of adjusting the pressure inside the chamber comprises the step of acting on the degree of opening of the fluid supply valve (V6) in order to maintain the pressure in the chamber equal to a preset value.

7. The method according to claim 5 or 6, wherein after said open-loop calibration phase, another closed-loop calibration phase is carried out. 8.- The method according to claim 7, wherein in the other closed-loop calibration phase, pressurized fluid is again supplied to the valve inlet (200) until the pressure present in the chamber (20) reaches the preset value; this other adjustment step comprises: acquiring the supply pressure (Pmeasured) of the valve (240); continuously controlling the movement of the pusher (30) to modify the position of the support seat (10) relative to the valve seat (6); Compare (250) the pressure (Pmeasured) with the target pressure set for the valve (Ptarge-J) and end the 5 valve calibration when the measured pressure is equal to or greater than the target; - continue the calibration phase when the measured pressure (Pmeasured) is below the target by actuating the continuous advance at low speed of the pusher until 10 said comparison gives a positive result.

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