Actuator for Valve

Valves are generally disposed in the course of passages of gas or a liquid for adjusting the flow rate thereof or controlling the opening and closing of the passages. There are instances where a disaster such as an earthquake or a fire may provoke an unforseen severe accident due to leak of combustible gas unless the gas passages are immediately closed. In such case, it is required to emergently close the valves simultaneously with the occurrence of a disaster. However, it is not actually possible to manually operate a plurality of valves simultaneously, specially in a state of disorder at the time of the occurrence of a disaster. Some measures to be taken have therefore been required.

In this connection, there has been proposed an actuator adapted to automatically close a valve by switching an electromagnetic clutch, using the retaining strength of a power spring which has been manually wound in advance. In such actuator, the power spring has to be manually wound in advance, taking much labor, and there is a risk of failure to wind the power spring. Further, the use of expensive electromagnetic clutch disadvantageously increases the manufacturing cost. In view of the foregoing, such actuator has not been put to practical use until now.

It is a first object of the invention to provide an actuator which overcomes these defects of the conventional actuator and which can be easily operated requiring no manual operation.

It is a second object of the invention to provide an actuator which can automatically close a valve with the use of the retaining strength of a power spring without a clutch operation, if power is shut off at the time of power failure or the like.

It is a third object of the invention to provide an actuator in which the driving force of a motor for rotating the body of a valve in the opening direction is utilized for winding a power spring.

It is a fourth object of the invention to provide an actuator adapted to close a valve by unwinding a power spring by the operation of an electromagnetic device such as an electromagnetic brake, if power is shut off at the time of power failure or the like, thus preventing an unforseen accident from happening.

The present invention is proposed in order to achieve these objects. The concrete arrangement of the invention will be understood from the following detailed description with reference to the attached drawings.

FIG. 1 is a side view of an actuator in accordance with the present invention mounted on a valve.

FIG. 2 is a perspective view of the actuator in FIG. 1 with the valve closed.

FIG. 3 is a perspective view of the actuator in FIG. 1 with the valve opened.

FIG. 4 is a longitudinal side view of an electromagnetic device.

The present invention comprises a casing 1, an output shaft 2 to be connected directly to a rotary shaft of the body of a valve A, the shaft 2 being pivotally supported in the casing 1, a gear 4 to be rotated in one direction only by a motor 3, an internal gear 5 having outer peripheral teeth 5.sub.1 meshed with the gear 4, the internal gear 5 being pivotally supported by the output shaft 2 and rotatable independently therefrom, a gear 7 meshed with inner peripheral teeth 5.sub.2 of the internal gear 5 and with a gear 6 secured to the output shaft 2, and gear 8 for pivotally supporting the gear 7 at a shaft 7.sub.1, the gear 8 being pivotally supported by the output shaft 2 such that the gear 8 is rotatable independently therefrom, a power spring 9 wound by the rotation of the output shaft 2 in the valve opening direction, and an electromagnetic device 10 for preventing the gear 8 from being rotated while power is supplied, and for permitting the gear 8 to be rotated when the power is shut OFF.

The motor 3 is arranged such that the rotary shaft is fixed by an internal brake mechanism while the motor is stopped operating, and such that the rotating force of the motor is transmitted to the gear 4 through reduction gears 3.sub.1 and 3.sub.2 and a shaft 3.sub.3. The gear 7 includes a larger diameter portion meshed with the inner peripheral teeth 5.sub.2 of the internal gear 5, and a smaller diameter portion meshed with the gear 6. The power spring 9 has an inner end secured to a shaft 12.sub.1 integral with a gear 12 meshed with a gear 11 secured to the output shaft 2, and an outer end suitably secured to the casing 1. The power spring 9 is adapted to be wound by the rotation of the output shaft 2 in the valve opening direction. The electromagnetic device 10 includes a rotary shaft 10.sub.1, a thin plate 10.sub.2 secured to the upper end of this rotary shaft, a ring-shape absorbing plate 10.sub.3 secured to this thin plate 10.sub.2, and an electromagnet 10.sub.4 for magnetically absorbing the absorbing plate 10.sub.3. By the excitation of the electromagnet 10.sub.4, the abosorbing plate 10.sub.3 is magnetically absorbed to the electromagnet 10.sub.4 to prevent the rotary shaft 10.sub.1 from being rotated. Together with a reduction gear, the electromagnetic device 10 is housed in the casing 1. A gear 10.sub.1c is mounted on a rotary shaft 10.sub.1a through a one-way clutch 10.sub.1b, the rotary shaft 10.sub.1a being connected to the rotary shaft 10.sub.1 through a reduction gear. The gear 10.sub.1c is meshed with the gear 8.

A rotation restricting cam 13 is secured to a portion of the output shaft 2 adjacent the lower end thereof. This cam 13 is arranged so as to be rotated forwardly and reversely within an angle of 90.degree. by a stopper 14 facing to the inside from the outside of the lower end of the casing 1.

A limit switch 15 is adapted to be turned OFF when the contact thereof is opened by a cam secured to the output shaft 2 when the output shaft 2 is rotated up to the valve opening position. The limit switch 15 is disposed for controlling the supply of power to the motor 3. A limit switch 16 is adapted to be turned ON when the contact is closed by a cam secured to the shaft 12.sub.1 for winding the power spring 9 when the shaft 12.sub.1 is rotated up to a position where the power spring 9 is sufficiently wound. The limit switch 16 is disposed for making sure that the spring 9 is sufficiently wound.

The following description will discuss how to use and operate the actuator in accordance with the present invention shown in the embodiment above-mentioned.

With the lower end of the output shaft 2 fitted in a fitting hole haviing a key groove in the upper end of the rotary shaft of the body of the valve A, the actuator in accordance with the present invention is attached to the valve A such that the rotary shaft of the valve and the output shaft 2 are integrally rotated.

When the main switch of a power supply if turned ON to supply power to the motor 3 with the body of the valve closed, the motor 3 is driven to rotate the gear 4. The internal gear 5 of which the outer peripheral teeth 5.sub.1 are meshed with the gear 4, is then rotated in the direction shown by an arrow. The gear 7 meshed with the inner peripheral teeth 5.sub.2 is also rotated. When the main switch is turned ON, power is also supplied to the electromagnet 10.sub.4 of the electromagnetic device 10. The excitation of the electromagnet 10.sub.4 prevents the gear 8 which pivotally supports the gear 7 at the shaft 7.sub.1, from being rotated. Therefore, the gear 7 is rotated as it is. The gear 6 meshed with the smaller diameter portion of the gear 7 and the output shaft 2 integral with the gear 6 are rotated in the valve opening direction. At this time, when the power spring 9 is wound and the output shaft 2 is rotated up to a position where the valve body is fully opened, power to the motor 3 is shut off by the operation of the limit 15. The motor 3 is then stopped operating and the rotary shaft is fixed by the internal brake mechanism to prevent the internal gear 5 from being rotated. Therefore, the output shaft 2 cannot be reversely rotated even though the output shaft 2 tends to be reversely rotated by the retaining strength of the power spring 9, and the power spring 9 is held as pressure-accumulated.

When the main switch is turned OFF or power to the electromagnet 10.sub.4 of the electromagnetic device 10 is shut off due to power failure, the absorbing plate 10.sub.3 magnetically absorbed by the electromagnet 10.sub.4 is separated therefrom. Therefore, the rotary shaft 10.sub.1a and the gear 10.sub.1c become free and the gear 8 becomes rotatable. Therefore, the gear 7 meshed with the gear 6 is meshed with the inner peripheral teeth 5.sub.2 of the internal gear 5, thus permitting the gear 7 to perform a so-called planetary motion, i.e. turning together with the gear 8 while turning on its axis. The output shaft 2 is rotated in the direction shown by a dotted line or in the valve A closing direction by the retaining strength of the power spring 9, so that the valve is closed. At this time, the absorbing plate 10.sub.3 integral with the rotary shaft 10.sub.1 is rotated at a high speed. However, when the output shaft 2 is rotated by 90.degree. and the cam 13 comes in contact with the stopper 14 to suddenly stop the rotation of the absorbing plate 10.sub.3, an unreasonable force is applied to the reduction gear by the force of inertia of the absorbing plate 10.sub.3. There is a risk of the reduction gear being damaged. However, the one-way clutch 10.sub.1b is disposed between the rotary shaft 10.sub.1a and the gear 10.sub.1c. Even though the gear 8 is stopped rotating in the course of rotation to stop the gear 10.sub.1c, the rotary shaft 10.sub.1a or the rotary shaft 10.sub.1 and the absorbing plate 10.sub.3 are run idle by the force of inertia under the action of this one-way clutch 10.sub.1b. No force is therefore applied to the reduction gear.

Thereafter, the operations above-mentioned are repeated for each opening/closing of the valve.

According to the actuator for a valve in accordance with the present invention as discussed hereinbefore, the valve is automatically closed when the main switch is turned OFF or the electricity is cut off while the valve body is opened. Therefore, if a disaster such as an earthquake, a fire or the like happens, the valve body is instantaneously closed to prevent a secondary accident from happening. When the actuators of the present invention are respectively attached to a plurality of valves, the opening/closing of the valves can be controlled at one place. Not only in case of emergency of a disaster, but also in a general use, the opening/closing of valves can be easily controlled. Thus, the present invention represents very practical advantages.