WO2010128952A2

WO2010128952A2 - Fail-safe valve actuator

Info

Publication number: WO2010128952A2
Application number: PCT/SI2010/000023
Authority: WO
Inventors: Peter Sever
Original assignee: Peter Sever
Priority date: 2009-05-04
Filing date: 2010-05-04
Publication date: 2010-11-11
Also published as: SI23058A; WO2010128952A3

Abstract

The fail-safe valve actuator drives an actuator stem (9) between the first and second positions while energizing the spring (5), whereby the holding device prevents backdriving of the nuts (10, 10', 10") after spring (5) has been energized and thus the holding device does not consume electric power in stand-by mode for sustaining the spring (5) in energized state. Hence the fail-safe actuator drives the actuator stem (9) from either of its positions to its other position for reconfiguring a valve between the first and second state without substantially energizing or de-energizing the spring (5). In the case of a power supply failure the device further comprise the release means, which causes the actuator stem (9) to be moved under the influence of de-energization of the spring (5) to one of its extreme positions after power supply fails and thereby to reconfigure the valve to one of its states (closed/open).

Description

PETER SEVER Toneta Pleja 4 9232 Crensovci Slovenia - EU

FAIL-SAFE VALVE ACTUATOR

Field of the Invention

The object of this patent application relates to linear actuators with an integrated safety function. A linear actuator is a device for controlled linear movement where the security feature means that upon failure of such an actuator the valve stem is moved in the predefined position. Such devices are used in industrial plants as well as in heating, ventilation and air-conditioning systems and also as vital components in various industrial applications, where the safety feature is extremely important.

Background of the Invention

Typical fail safe valve actuators which can close or open a valve in an emergency have a drive mechanism for actuating the valve stem in a controlled manner and a preloaded spring for causing the valve actuator to rapidly close or open the valve in case of a failure.

According to applicable standards for fail safe actuators, using traditional energy carriers (e.g. rechargeable battery) is not allowed for safety function execution. For this reason, the main technical problem of such devices is supporting relatively large forces produced by resilient means to execute the security feature, whereby the spring is commonly used as resilient means. However, a problem with these actuators is that although the spring is energized by drive mechanism, the drive mechanism also works against the spring during each complete valve operating cycle causing high power consumption. Therefore the technical problem of prior art fail safe actuators is that all relevant devices comprise a locking means (e.g. electromagnet) which is directly interconnected with release means and furthermore with energized resilient means.

The objective of the present invention is therefore to provide a fail-safe valve actuator for operating a valve in a controlled manner, which can rapidly close or open a valve and which eliminates the lack of a device that also provides: a) energy-efficiency: this means, that the device in standby mode does not consume electricity for maintaining and preserving the energy of energized resilient means, essential for fail-safe execution.

b) autonomous operation: this means, that the device enables the positioning of the valve stem between two extreme positions by manual override means, even in case of a power failure.

The International patent register comprises a greater number of devices with a safety feature. These actuators are powered by various energy sources; while they are primarily driven by a rotational electric motor, there are also hydraulic actuators, pneumatic actuators, devices driven directly by an electromagnet and various combinations thereof.

WO 2004/065832 represents the state of the art fail safe actuator, whereby the device in preferred embodiment is integrated into the valves body. The energy for the fail safe feature execution is stored in the spring, which is energized and locked in a compressed state by an electromagnet. Still, there exist some imperfections of such a device, i.e.:

a) the power of the security feature and the energy for the fail safe execution is directly and completely dependent of the maximum holding force of the electromagnet, that holds the spring in a compressed state;

b) for normal usage with bigger lateral forces, such an actuator would have an extremely large and powerful electromagnet, which would represents a large and permanent consumer of electric energy; and

c) such an actuator does not allow manual override in case of a power failure.

Summary of the Invention

According to aspect of the present invention there is provided a failsafe valve actuator, characterized by:

• an actuating member movable between first and second positions to reconfigure a valve between the first and second state;

• drive means adapted to operatively engage the actuating member and arranged to drive the valve between its first and second state;

• resilient means energizable by the drive means;

• framework means as an assembly of structural elements essential for device construction;

• locking means for locking the resilient means in an energized state, the locking means permitting the drive means to drive the actuating member from either of its positions to its other position without substantially energizing or de-energizing the resilient means when the resilient means is locked by the locking means;

• release means for releasing the resilient means from the locking means, to cause the actuating member to be moved under the influence of de-energization of the resilient means to one of its positions and thereby reconfigure the valve from one to the other of its states; and

• load transformation means for transforming the actuating force of resilient means and reducing the power needed to withhold the force produced by resilient means in the energized state. It is essential to notice that the power provided by the holding device is evidently smaller than the power provided by the energized resilient means (e.g. conversion of thrust loads into torque loads by backdriving of a non self-locking threaded engagement means).

The valve actuator may include containment means for substantially containing the drive means, the resilient means, the framework means, the locking means, the release means and the load transformation means, whereby the actuating member is being partly contained within the containment means and is movable relative to the containment means. The containment means may comprise a waterproof housing. The fail-safe valve actuator may further include additional load transfer means which may be mounted on and/or connected to framework means for providing a strong and rigid construction.

Conveniently, the drive means operably engages the actuating member by threaded engagement means. The actuating member may have a screw shaft and the drive means may have threaded means for engaging the screw shaft or vice versa. Drive means may further comprise manual override means, which may include gears and additional rotating shaft, whereby manual override is possible even after fail-safe action has been triggered. Power drive is preferably provided by a positionable BLDC electric motor, whereby other sources and types of power are possible (e.g. DC motor, reversible synchronous motor or stepper motor).

The resilient means are used to close or open the valve in an emergency. The resilient means may comprise at least one spring which is adapted to be energized and locked in place by the locking means, allowing the valve to be subsequently operated without working against the or each spring. This results in a fail-safe valve actuator having a zero power consumption of a holding device in a stand-by mode, after resilient means being locked in place.

An actuating member is an element of the device that interconnects the fail-safe actuator with the valve stem and transfers the linear loads from one to another between two extreme positions.

The locking means and the release means of the fail-safe actuator may be designed as a trigger mechanism which may include a subsidiary drive. Such trigger mechanism may further comprise linear and/or rotational brake.

According to another aspect of the present invention a method is provided to operate a fail-safe valve actuator with zero power consumption of a holding device in stand-by mode, characterized by the following steps:

driving an actuating member movable between the first and second positions and energizing the resilient means;

locking the resilient means in an energized state, whereby the holding device in stand-by mode does not consume power;

driving the actuating member from either of its positions to its other position for reconfiguring a valve between the first and second state without substantially energizing or de-energizing the resilient means; and releasing the resilient means from being locked after power supply fails, causing the actuating member to be moved under the influence of de-energization of the resilient means to one of its positions and thereby reconfigure the valve to one of its extreme states (e.g. closed or open).

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, whereby for clarity of figures the housing of the device and valve with its valve stem are not shown.

Brief description of the drawings

Figure 1 is an isometric view of the fail-safe valve actuator according to a preferred embodiment of the invention with a view from the top.

Figure 2 is an isometric view of a fail-safe valve actuator with a view from the bottom.

Figure 3 is an isometric view of a fail-safe valve actuator with a view from the top, whereby for clarity of the figure the spring (5) is not shown.

Figure 4 is a top view of a fail-safe valve actuator, whereby the line A-A for further cross-sectional figures is defined.

Figure 5 is a transverse cross-section taken along line A-A of Figure 4, whereby the device is shown in a stand-by mode with the spring (5) in energized state and the actuator stem (9) in its upper extreme position.

Figure 6 is a transverse cross-section taken along line A-A of Figure 4, whereby the device is shown in stand-by mode with the spring (5) in energized state and the actuator stem (9) in its lower extreme position.

Figure 7 is a transverse cross-section taken along line A-A of Figure 4, whereby the device is shown in a state after fail-safe action was executed whereby the spring (5) was de-energized.

Figure 8 is a scheme of release means electronics, which enables the activation and positioning of the release means after power supply fails. Detailed description of a preferential embodiment

Referring to Figure 1 of the accompanying drawings, the fail-safe valve actuator comprises the drive (6) whose rotating movement is converted to the rectilinear movement by threaded engagement means (15), which preferably comprise a threaded spindle and an appurtenant nut on the actuator stem (9). The drive (6) (preferably electric planetary gear motor) is mounted on a flange (2B) within the seat (2C) of the main plate (2). The gear shaft of the drive (6), whose rotation axis is identical with a longitudinal axis (S), is connected to the threaded engagement means (15) with integrated driven gear (14), which is furthermore mounted to the main plate (2) via an apparatus (preferably thrust bearing (16), (17)) for bearing the axial loads. Therefore the motion in a preferred embodiment is transmitted to the actuator stem (9) by the planetary gear motor and threaded engagement means (15), preferably a ball screw with an appurtenant ball nut being in an anti-rotational engagement.

Resilient means of a fail-safe actuator are mounted between two elements of the framework means, whereby it is important to notice, that it is possible to change the direction of an actuating force by changing the type of the spring (5) or by changing the installation position of the spring (5) within the framework means. Referring to Figure 1-7 the spring (5) is a helical compression spring, mounted between the main plate (2) and the top plate (1), whereby the spring (5) is acting in the movement direction of the actuator stem (9), causing displacement of the actuator stem (9) from the upper extreme position (IR-1) to the lower extreme position (IR-2) by de-energizing the spring (5).

To provide the fail-safe actuator with zero power consumption of a holding device in stand-by mode, the actuator further comprises the load transformation means for transforming the actuating force of an energized spring (5) and reducing the power needed to withhold the force produced by resilient means in the energized state. The transformation means may comprise non self-locking threaded means (preferably non self-locking screw shafts (4, 4', 4") and a belt (11) for providing the synchronous rotation of appurtenant nuts (10, 10', 10")). The nuts (10, 10', 10") are designed as a belt (11) pulley mounted between the main plate (2) and the flange (2B) while they are installed on appurtenant non self-locking screw shafts (4, 4', 4") for backdriving under the load of the energized spring (5).

The locking means may further comprise the holding device, assembled from a subsidiary drive (preferably controllable PWM servo motor (8) mounted within an adapter (2D)) with an eccentric element mounted on the shaft therefore, and a clamping mechanism, comprising the free block member (8A) and fixed block member (8B). Because the element is being mounted eccentrically on the subsidiary drive shaft, the rotational movement is converted into the rectilinear movement of the free block member (8A) relative to the fixed block member (8B) and subsequently clamping the belt (11 ) and blocking or unblocking rotation of the nuts (10, 10', 10"). To sustain loads with minimum power required after the spring (5) has been energized and positioned, the disc spring washers are inserted between the nuts (10, 10', 10") and framework means to minimize the holding torque required for blocking the rotation of the nuts (10, 10', 10"), whereby the disc spring washers are acting as a rotational mechanical brake. The same result can be obtained if a belt tensioner or other mechanical brake is applied to the belt (11).

Some of the release means of the fail-safe actuator may be technically the same as the locking means, whereby the energy for triggering the clamping mechanism and subsequently releasing the energized spring (5) is provided by the electronics, which may further comprise the capacitors with stored electric energy, that powers the subsidiary drive to unlock the clamping mechanism, which releases the belt (11) and therefore the nuts (10, 10', 10") are free to rotate by backdriving. It can be understood, that with the rotation of the nuts (10, 10', 10") along the non self-locking screw shafts (4, 4', 4"), the main plate (2) is moved from one extreme position to another where subsequently the actuator stem (9) is moved from the coincidental like upper extreme position (IR-1) to the lower extreme position (IR-2), causing the valve being rapidly closed in a controlled manner by the fail-safe valve actuator.

The drive means may further comprise manual override means, where manual override means comprise drive gear (12) and appurtenant hexagonal rotating shaft (7) upon toque may be applied by a hex wrench. To provide the rotational engagement between drive gear (12) and driven gear (14) in any coincidental position along the longitudinal axis (S), the manual override means may further comprise a bushing (13) for positioning the drive gear (12) together with main plate (2). If adequate length of actuator stem (9) and threaded engagement means (15) is provided the manual override feature is possible even after power supply fails, where additional mechanical block member may be added to securely prevent the rotation of nuts (10, 10', 10").

It can be understood, that the torque actuated by the rotation of the drives (6) shaft is transferred to the framework means by anti-rotational engagement of threaded engagement means (15). For additional anti-rotational support the main plate (2) and the base plate (3) may be designed in such manner, that the torque is transferred to the framework also by other individual elements of the framework means. For example, the engagement between the actuator stem (9) and the base plate (3) can be designed as a spline shaft (2A) connection with straight flanks in various ways. If it is acceptable, the fail-safe valve actuator should rather comprise an additional linear slide shaft with appurtenant linear bearings, which provides a rigid and reliable construction of such a device.

In a preferred embodiment of a fail-safe valve actuator the base plate (3) has a central aperture through which the actuator stem (9) is displaceable. The base plate (3) may be designed as a form-fit attachment adapter for installing the fail-safe actuator to various valve series. Therefore the base plate (3) in a preferred embodiment may comprise an adapter (3B) with three connecting plates (3A) and a central orifice (3C) for providing the valve stem passage and an aperture (3D) for the installation of the device on the valve. The valve adapter (3B) in a preferred embodiment has a three-point connection with a valve neck, provided by means of three fasteners equally distributed around the longitudinal axis (S); a similar connection is provided for a stem connection, where the valve stem is connected to the actuator stem (9). Each of the connecting plates (3A) may further comprise a travel indicator scale.

Referring to figures 1-7 for an optimal load distribution of the energized spring (5) three non self- locking screw shafts (4, 4', 4") are rigidly connected to the top plate (1) and the base plate (3); furthermore referring to Figure 4 non self-locking screw shafts (4, 4', 4") are equally distributed around the longitudinal axis (S), whereby the main plate (2) is movable along the longitudinal axis (S) between two extreme positions by principle of backdriving the nuts (10, 10', 10").

Referring to Figure 8 a release means, more exactly a subsidiary drive (M) is connected to the electronics, where electrical circuits furthermore comprise a DPDT relay (E), a capacitor (C), a diode of the primary circuit (D1), a diode of the secondary circuit (D2), a resistor of the primary circuit (R1) and a resistor of the secondary circuit (R2). In a normal mode situation, when the fail-safe actuator is connected with the power supply and after the release means has been energized by drive means manipulated by electronic logic, the subsidiary drive (M) is preferably manipulated with pulse width modulation by a microcontroller of electronic logic. In such manner the resilient means can be locked in an energized state by locking means, more exactly by a clamping device, as described before. For triggering the resilient means, the subsidiary drive (M) is via the DPTD relay (E) connected to the second electric circuit, where the subsidiary drive (M) is powered by the capacitor (C). To provide the energy for the subsidiary drive (M) after power supply fails, the electronics comprise the primary diode (D1) for preventing energizing the relay after power supply fails; and the resistor (R1) for current inrush elimination. Furthermore the electronics comprise the secondary circuit diode (D2) and the secondary circuit resistor (R2) to minimize the switch-off time of the DPDT relay (E).

Referring to Figures 1-8, now the operation of the fail-safe valve actuator will be described.

The fail-safe valve actuator is initially in its neutral position with the spring (5) de-energized in its initial, pre-stressed state as shown in Figure 7, where the actuator stem (9) is in its lower extreme position (IR-2) and the valve is closed.

The first step is to energize the spring (5) by compressing it. The drive (6) is activated by the electronic drive controller, which causes the drive (6) and accompanying threaded engagement means (15) to rotate in the first direction. It is important to notice, that the drive (6) is manipulated by the electronics and may be activated manually or by a control signal being sent to the electronic drive controller. Thus, the spring (5) transfers a load to the top plate (1) and to the main plate (2), the resulting axial load is born by the thrust bearing (16). Referring to Figure 7 the actuator stem (9) abuts the base plate (3) and the rotation of the threaded engagement means (15) causes the main plate (2), to which the threaded screw shaft is attached via the driven gear (14), to be moved in an upward direction relative to both the actuator stem (9) and the base plate (3), to the position shown in Figure 6. Furthermore, when the position shown in Figure 6 is established and the electronic drive controller determines that the spring (5) is energized and the main plate (2) is in its upper extreme position, the drive (6) stops to rotate.

Secondly, to preserve the spring (5) in an energized state, the electronics activates the subsidiary drive (M) which clamps the belt (11) with the clamping device and subsequently prevents the nuts (10, 10', 10") to rotate, more exactly to backdrive. After the spring (5) has been energized and the belt (11) is being blocked in place, the fail-safe actuator is in ready or stand-by mode, where the fail-safe actuator may retract or extend the actuator stem (9) regarding to the direction of the drive (6) shaft rotation. Referring to the Figures 5 and 6 the valve can be opened or closed in a controlled manner by control signals being sent to the electronics, where the actuator stem (9) moves the valve stem between the first and second state without substantially energizing or de-energizing the spring (5).

Furthermore, referring to Figure 8 the subsidiary drive (M) is via the DPTD relay (E) connected to the second electric circuit, where the subsidiary drive (M) is powered by the capacitor (C) after power supply fails. The servo motor (8) will afterwards release the belt (11) from the clamping device thus enable the nuts (10, 10', 10") to backdrive, while the spring (5) is acting in the direction of the actuator stem (9) movement, causing displacement of the actuator stem (9) from the upper extreme position (IR-1) to the lower extreme position (IR-2) by de-energizing the spring (5), whereby the valve being consequently repositioned to the predefined state.

Whilst a particular embodiment has been described, it will be understood that various modifications may be made without departing from the scope of the invention. For example, the valve actuator may be configured to open a valve in an emergency instead of closing the valve, whereby the state of the valve depends also on the type of the valve. Furthermore, the drive (6) may be installed on any other element of framework means, instead on the main plate (2), whereby the transmission of power may be provided by additional gears, belt, chain or any other drive transmission means. The resilient means may comprise instead of the compression spring extension spring, which would hence change the direction of actuation force. Furthermore the threaded engagement means (15) may be instead of a ball-screw type and appurtenant nut provided by an acme lead screw and appurtenant nut, a trapezoidal lead screw and appurtenant nut or a roller screw and appurtenant nut. Furthermore, non self-locking threaded engagement means, more exactly non self-locking screw shafts (4, 4', 4") and an appurtenant nuts (10, 10', 10"), may be used instead of a lead-screw type, a ball-screw or a roller- screw type. Furthermore, the holding device may be instead of the servo motor (8) provided by an electric linear or rotational brake on a basis of an electromagnet.

Claims

1. Fail-safe valve actuator comprising an actuating member movable between first and second positions to reconfigure a valve between the first and second state, controlled by drive means adapted to operatively engage the actuating member and arranged to drive the valve between its first and second state, thus the resilient means are energizable by the drive means while said resilient means being mounted within the framework means comprising an assembly of structural elements essential for solid device construction, in which the locking means locks the resilient means in an energized state while permitting the drive means to drive the actuating member from either of its positions to its other position without substantially energizing or de-energizing the resilient means, where the release means for releasing the resilient means from the locking means in a case of a power supply failure subsequently causes the actuating member to be moved under the influence of de-energization of the resilient means to one of its extreme positions and thereby reconfigure the valve from one to the other of its states characterized in that the fail-safe actuator further comprise a load transformation means for transforming the actuating force of resilient means and reducing the power needed to withhold the force produced by resilient means in the energized state, where it is essential to notice that the actuating force of resilient means is converted into torque loads by backdriving of a non self-locking threaded engagement means and thus the power provided by the holding device for locking the resilient means in energized state is evidently smaller than the power provided by the energized resilient means.

2. Fail-safe valve actuator as in Claim 1 , characterized in that the rotating movement of drive (6) is converted to the rectilinear movement of the actuator stem (9) by threaded engagement means (15), being displaceable in the movement direction of the actuator stem (9).

3. Fail-safe valve actuator as in Claim 2, characterized in that said threaded engagement means (15) are ball-screw type, comprising a ball-screw shaft and an appurtenant ball-screw nut.

4. Fail-safe valve actuator as in Claim 2, characterized in that said threaded engagement means (15) are roller-screw type, comprising a roller-screw shaft and an appurtenant roller- screw nut.

5. Fail-safe valve actuator as in Claim 2, characterized in that said threaded engagement means (15) are lead-screw type, comprising a lead-screw shaft and an appurtenant lead- screw nut.

6. Fail-safe valve actuator as in Claim 1 , characterized in that said framework means comprise a top plate (1), a main plate (2) and a base plate (3), wherein said main plate (2) being movable between first and second positions to reconfigure a valve between the first and second state; furthermore the base plate (3) has a central aperture through which the actuator stem (9) is displaceable, whereby the base plate (3) is designed as a form-fit attachment adapter for installing the fail-safe actuator to various valve series and therefore the base plate (3) comprise an adapter (3B) with three connecting plates (3A) and a central orifice (3C) for providing the valve stem passage and an aperture (3D) for the installation of the device on the valve, whereby the valve adapter (3B) has a three-point connection with a valve neck, provided by means of three fasteners equally distributed around the longitudinal axis (S); hence a similar connection is provided for a stem connection, where the valve stem is connected to the actuator stem (9) also by means of three fasteners equally distributed around the longitudinal axis (S); furthermore each of the connecting plates (3A) comprise a travel indicator scale; and furthermore the fail-safe valve actuator comprise the linear slide shaft with appurtenant linear bearings for moving the main plate (2) along the longitudinal axis (S)₁ while providing a rigid and solid construction of the framework means.

7. Fail-safe valve actuator as in Claim 6, characterized in that the drive (6) is installed on the main plate (2) with the flange (2B).

8. Fail-safe valve actuator as in Claim 7, characterized in that said drive (6) is the BLDC electric gear-motor, whereby the gear shaft of the drive (6), whose rotation axis is identical with a longitudinal axis (S), is via torque transmission means coupled to the threaded engagement means (15) with integrated driven gear (14), which is furthermore mounted to the main plate (2) via an apparatus for bearing the axial loads, thus the power is transmitted to the actuator stem (9) by the planetary gear motor and threaded engagement means (15) being in an anti-rotational engagement with framework means.

9. Fail-safe valve actuator as in Claim 6, characterized in that the resilient means are installed between top plate (1) and main plate (2).

10. Fail-safe valve actuator as in Claim 6, characterized in that the resilient means are installed between base plate (3) and main plate (2).

11. Fail-safe valve actuator as in Claim 1 , characterized in that said resilient means comprise at least one spring (5).

12. Fail-safe valve actuator as in Claim 11 , characterized in that said spring (5) is a compression spring.

13. Fail-safe valve actuator as in Claim 11 , characterized in that said spring (5) is an extension spring.

14. Fail-safe valve actuator as in Claim 1 , characterized in that said load transformation means comprise a least one non self-locking screw shaft (4, 4', 4") and appurtenant nut (10, 10', 10").

15. Fail-safe valve actuator as in Claim 14, characterized in that said load transformation means comprise three non self-locking screw shafts (4, 4', 4") and appurtenant nuts (10, 10', 10"), which are connected with belt (11) for synchronous rotational movement of nuts (10, 10', 10") by backdriving, wherefore the nuts (10, 10', 10") are designed as a belt (11) pulleys; furthermore said nuts (10, 10', 10") are installed on appurtenant non self-locking screw shafts (4, 4', 4") between the main plate (2) and the flange (2B), where the disc spring washers are inserted between individual nut (10, 10', 10") and between framework means, to minimize the holding torque required for blocking the nuts (10, 10', 10") while the disk spring washers are acting as mechanical rotational brake, hence to prevent the nuts (10, 10', 10") to rotate by backdriving; and furthermore for an optimal load distribution of the energized spring (5) three non self-locking screw shafts (4, 4', 4") are rigidly connected to the top plate (1) and the base plate (3), whereby non self-locking screw shafts (4, 4', 4") are equally distributed around the longitudinal axis (S), thus the main plate (2) is movable along the longitudinal axis (S) between two extreme positions by principle of backdriving the nuts (10, 10', 10").

16. Fail-safe valve actuator as in Claim 15, characterized in that said non self-locking screw shafts (4, 4', 4") and appurtenant nuts (10, 10', 10") are lead-screw type.

17. Fail-safe valve actuator as in Claim 1 , characterized in that said locking means comprise a holding device with subsidiary drive (M), which blocks the rotation of nuts (10, 10', 10") after spring (5) has been energized by drive means.

18. Fail-safe valve actuator as in Claim 17, characterized in that said holding device comprise a controllable electric servo motor (8) with an eccentric element mounted on the shaft therefore, where said clamping mechanism further comprise a free block member (8A) and fixed block member (8B), wherein the rotational movement of servo motor (8) is converted into rectilinear movement of the free block member (8A) relative to the fixed block member (8B) and relative to the belt (11), wherein such clamping mechanism is blocking the rotation of nuts (10, 10', 10") by fastening the belt (11 ) in place, hence preserving the spring (5) in energized state.

19. Fail-safe valve actuator as in Claim 1 , characterized in that the device further comprise the electronics logic for controlling the drive means and subsidiary drive (M) of the release means, whereby said electronic comprise a microcontroller, a drive (6), a subsidiary drive (M)₁ a DPDT relay (E), a capacitor (C), a diode of the primary circuit (D1), a diode of the secondary circuit (D2), a resistor of the primary circuit (R1) and a resistor of the secondary circuit (R2), whereby in a normal mode situation, when the fail-safe actuator is connected with the power supply and after the release means has been energized by drive means, the subsidiary drive (M) locks the resilient means in an energized state with locking means, more exactly by a clamping device, whereby for triggering the resilient means, the subsidiary drive (M) is via the DPTD relay (E) connected to the second electric circuit, where the subsidiary drive (M) is powered by the capacitor (C) to provide the energy for the subsidiary drive (M) after power supply fails; furthermore, the electronics comprise the primary diode (D1) for preventing energizing the relay after power supply fails; and the resistor (R1) for current inrush elimination, whereby the electronics comprise the secondary circuit diode (D2) and the secondary circuit resistor (R2) to minimize the switch-off time of the DPDT relay (E).

20. Fail-safe valve actuator as in Claim 22, characterized in that said subsidiary drive (M) is the servo motor (8), controllable by a microcontroller of electronics logic with pulse width modulation.

21. Fail-safe valve actuator as in Claim 1 , characterized in that said holding device is the electromagnetic brake, which prevents the nuts (10, 10', 10") to rotate by backdriving, after spring (5) has been energized, whereby the backdriving of nuts (10, 10', 10") is manipulated by supply engagement of electromagnetic brake, controlled by electronics.

22. Fail-safe valve actuator as in Claim 1 , characterized in that said drive means further comprise manual override means, in which the manual override means comprise the drive gear (12) and appurtenant hexagonal rotating shaft (7) upon toque may be applied by a hex wrench, whereby the torque is transferred from drive gear (12) to driven gear (14) by rotational engagement, while the manual override means further comprise a bushing (13) for positioning the drive gear (12) together with the driven gear (14) and main plate (2) in any coincidental position along the longitudinal axis (S); furthermore the adequate length of actuator stem (9) and threaded engagement means (15) is provided to drive the actuator stem (9) between two extreme positions without electric power supply, where the manual override means further comprise additional mechanical block member to securely prevent the backdriving, more exactly the rotation of nuts (10, 10', 10").

23. Fail-safe valve actuator as in Claim 1 , characterized in that the device further comprise the containment means for substantially containing the drive means, the resilient means, the framework means, the locking means, the release means and the load transformation means, whereby the actuating member is being partly contained within the containment means and is movable relative to the containment means; hence the containment means comprise a waterproof housing.

24. A method of operating a fail-safe valve actuator, characterized by steps of: driving an actuating member movable between the first and second positions and energizing the resilient means; locking the resilient means in an energized state, whereby the holding device in standby mode does not consume power; driving the actuating member from either of its positions to its other position for reconfiguring a valve between the first and second state without substantially energizing or de-energizing the resilient means; and releasing the resilient means from being locked after power supply fails, causing the actuating member to be moved under the influence of de-energization of the resilient means to one of its positions and thereby reconfigure the valve to one of its states.