Machine element or mechanism – Gearing – Directly cooperating gears
Patent
1993-12-27
1996-03-12
Herrmann, Allan D.
Machine element or mechanism
Gearing
Directly cooperating gears
74 2, 185 40R, 251 69, 251 71, F16K 3104, G05G 1700
Patent
active
054976723
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to an actuator for valves, and more particularly for gate valves which may be used to control flow within oil or gas pipelines either above or below sea level.
Known systems used both above and below sea level for controlling the opening and closing of gate valves are either hydraulic, pneumatic or electro-hydraulic actuators, and the most common of these is the hydraulic type. These actuators generally utilize an externally controlled flow of hydraulic fluid, under pressure, to drive a piston within an actuator cylinder. This cylinder compresses a spring stack and moves the valve stem to open or close the valve depending on its configuration. In an emergency situation when the valve must be shut quickly, the spring force can be used to achieve this.
However, hydraulic actuators have a number of operational disadvantages that would make the actuator unsuitable for some subsea applications. For example, as the distance between the hydraulic actuator and the top-side control center increases, the amount of hydraulic fluid needed to fill the lines and operate the valve also increases. Over long distances the fluid can lose pressure and therefore accumulators have to be installed close to the actuator to back up the pressure. Within some existing systems the time between a signal being sent from a control center and the actuator responding to the signal can be a matter of minutes, which in emergency situations can be too long. Furthermore, when the distance between the two sites reaches an optimum length, the hydraulic actuator will not be able to operate at all. An increase in water depth can also affect the actuator performance. The cost and size of the hydraulic lines and umbilicals also greatly increase as the operational depths and distances compound. It has therefore become apparent that a new design of actuator is required that will not be affected by depth/distance and that will have a fast response time, and it has been decided that an all electric valve actuator will meet these requirements.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a valve actuator which operates solely by electricity and which has a simple and cost-effective construction.
Accordingly, the present invention consists in a valve actuator comprising a stem extending through the actuator for coupling to the valve such that axial movement of the stem opens and closes the valve, an outer shaft arranged coaxially around the stem and in threaded engagement therewith, means coupling the shaft to an electric motor to cause rotational and thus axial movement of the shaft relative to the stem against a spring bias, and a solenoid-actuated latching mechanism for releasably retaining the shaft in a predetermined position with the spring held in a compressed state, such that further rotation of the shaft causes reciprocating axial movement of the stem relative to the shaft to actuate the valve, and de-activation of the solenoid-actuated mechanism releases the shaft to allow axial movement of both the shaft and the stem, under action of the spring, in order to close the valve.
In a preferred embodiment, the latching mechanism includes a cap retaining the spring and being connected to one end of the shaft, the cap having one or more recesses formed in a surface thereof, and a wedge member moved by one or more solenoids to push and hold a plurality of retaining members, for example ball bearings, into engagement with the recess or recesses in order to effect the latching action. The wedge member may be formed with an angled surface, the angle of which is dependent on the force of the spring as compared to the holding force of the one or more solenoids. The angle of the wedge member may be arranged so as to provide a sufficient mechanical advantage to enable the one or more solenoids with a relatively low holding force to retain the spring in its compressed state. In a preferred arrangement, wherein the retaining members are ball bearings made of steel,
REFERENCES:
patent: 3512421 (1970-05-01), Anderson
patent: 3518891 (1970-07-01), Denkowski
Appleford David E.
Engerran David
Alpha Thames Engineering Limited
Herrmann Allan D.
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