Fluid pressure actuator having position setting means

Details Fluid pressure actuator having position setting means Fluid pressure actuator having position setting means

1984-09-19

1986-01-28

Yeung, James C.

Valves and valve actuation

Fluid actuated or retarded

With mechanical movement between actuator and valve

251288, F16K 2104

Patent

active

045666709

DESCRIPTION:

BRIEF SUMMARY
FIELD OF INVENTION

The present invention relates to a fluid pressure actuator, e.g. for regulating valves, of the kind which includes a cylinder which is defined by end-walls and in which two pistons are arranged for movement towards and away from one another, said pistons having arranged thereon axially extending toothed rack portions the teeth of which mesh with a toothed wheel mounted on an actuating member which is journalled for rotation in and passes sealingly through at least one cylinder wall, so as to extend transversely to the longitudinal axes of said cylinders, and which further includes at least one passage for supplying pressure fluid to the cylinder space between the pistons.


BACKGROUND ART

Actuators of this kind are known through for instance EP A1 0 040 976 (Warnett) and U.S. Pat. No. 4,087,074 (Massey et al).
An actuator of this kind forms a compact and reliable unit for controlling various industrial processes and different kinds of apparatus.
Such an actuator is normally used to regulate valves, e.g. ball valves. In its simplest form, the actuator can, for example, rotate the actuating member through 90.degree., said member being connected to the valve slide, either directly or indirectly.
The actuating member can be rotated against the action of a spring, whereupon, if the fluid pressure is relieved, the pistons are returned to their zero-position by means of springs arranged in the rack portions.
The pistons, however, can also be returned to their zero-position under the influence of fluid pressure, either in addition to the springs or in place of said springs, whereupon the cylinder space between the end-walls of the actuator and respective pistons is placed under pressure via passages arranged in the cylinder wall and the end-walls, while de-pressurizing the space between the pistons.
It is often found subsequent to mounting the actuator, that the terminal positions of the pistons need adjusting, particularly when the actuator is to be used for regulating valves.
Hitherto, it has only been possible to adjust the outer terminal positions of the pistons, i.e. the positions in which the space between the pistons is under pressure and the pistons are located in the vicinity of their respective adjacent end-walls.
In this respect, it is possible to make such adjustments with known actuators by arranging in one of the end-walls of the actuator, preferably centrally of said wall, an adjusting means in the form of a screw, which projects away from said end-wall, into the cylinder chamber.
Thus, if the surface of the piston is located at a distance from the inner surface of the end-wall when said piston strikes against the screw, it is possible to adjust the stroke of the piston by turning the screw once or twice in one or the other direction. In practice, this normally corresponds to a 2.degree.-3.degree. rotation of the actuating member.
At present there is no possibility of making a similar adjustment when the pistons are located in their fully retracted position, corresponding to the zero-position of the actuating member.


OBJECT OF INVENTION

The possibility of making adjustments when the actuating member is in its zero-position, subsequent to mounting the actuator, is often desirable, particularly when regulating ball valves. The least little clearance in this position unavoidably results in the undesirable leakage of fluid, which can have extremely difficult consequences.


BRIEF DISCLOSURE OF THE INVENTION

The present invention affords a simple and reliable solution to the aforementioned problem. Accordingly, in its widest aspect the invention is mainly characterized in that one of the pistons is provided with means, e.g. a screw, which is arranged to engage the toothed rack portion of the other piston, so as to enable the pistons to be adjusted relative to one another in their fully retracted position. In this respect, the length of the rack portion on respective pistons is adjusted so that in the zero-position of the actuating member there is a clearance between the outer end

REFERENCES:
patent: 1037228 (1912-09-01), Fitts
patent: 3104862 (1963-09-01), Pearson et al.
patent: 3107080 (1963-10-01), Priese
patent: 4423752 (1984-01-01), Psarouthakis

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