WO1993015344A1

WO1993015344A1 - Valve switch box assembly

Info

Publication number: WO1993015344A1
Application number: PCT/GB1993/000182
Authority: WO
Inventors: Brian Edward Prince
Original assignee: Saunders Valve Company Limited
Priority date: 1992-01-28
Filing date: 1993-01-28
Publication date: 1993-08-05
Also published as: GB2263754A; GB9201733D0; AU3365193A

Abstract

A valve switch box assembly comprises a spindle (25) movable linearly between a first position and a second position in response to movement of an associated valve stem (38); at least one cam (4) mounted in the switch box and mechanically coupled to the spindle for rotation by the spindle in response to linear movement of the spindle; and at least one micro-switch (14) operable by the cam.

Description

VALVE SWITCH BOX ASSEMBLY

The present invention relates to a valve switch box assembly for use with a valve actuator, and more particularly for use with a linear valve actuator.

Linear valve actuators are used to effect the opening and closing of a number of types of valve such as globe valves, gate valves, needle valves and diaphragm valves, by the linear movement of a valve stem.

Typically, a switch box may be provided to house one or more switches for sensing and/or controlling the position of the valve stem. Typically, such a switch box may house a pair of micro-switches which are operated by contact with the valve stem or an extension of the valve stem. The switches may be used to drive remote indicators or control an actuator. For example, if the valve is open and a closing signal is sent to an electrically operated actuator, the actuator will typically drive the valve stem in the closing direction until a micro-switch in the switch box is actuated whereupon power to the actuator is disconnected.

The use of micro-switches driven by direct contact with the valve stem or an extension of the valve stem presents a number of difficulties. Firstly, adjustment of the position of the micro-switches is critical to ensure reliable indication of the valve position. Because of manufacturing tolerances within the components it may be necessary to adjust each micro-switch individually after the valve has been assembled, and to re¬ adjust the position of the micro-switches in response to long term deformation of, e.g., the closure diaphragm. Also, if the valve stem travel is excessive in one direction, e.g. , as a result of failure of some component, the micro-switches themselves may be engaged forcibly by the valve stem or an element secured to the valve stem resulting in damage to the micro-switches.

According to one aspect of the present invention there is provided a valve switch box assembly comprising a spindle movable linearly between a first position and a second position in response to movement of an associated valve stem; at least one cam mounted in the switch box and mechanically coupled to the spindle for rotation by the spindle in response to linear movement of the spindle; and at least one micro-switch operable by the cam.

With the switch box according to the present invention the cam arrangement will act to amplify the movement of the spindle thereby rendering accurate positioning of the micro-switches relatively simple. Further, in the event of over travel of the spindle the cam will not impose excessive forces on the micro-switches and accordingly damage to the micro-switches will be prevented.

An embodiment of the invention will now be described in more detail by way of example only to the accompanying drawings, in which:

Figure 1 is a cross-sectional side view of a valve switch box assembly according to the present invention;

Figure 2 shows an axial cross-sectional view of the switch box assembly of Figure 1;

Figure 3 shows a view taken on line III-III in Figure 2;

Figure 4 shows detail of an alternative mounting adapter for the assembly to that shown in Figures 1 to 3; and

Figure 5 is a partially cut away side view of the switch box assembly of Figure 1 with some additional features.

Referring first to Figure 1, a valve switch box assembly comprises a housing which is formed in two parts as an upper section 11 and a lower section 13. The housing sections are preferably formed as castings. A central spindle 25 passes through the housing and is supported in a main spindle bearing 27. Mounted inside the switch box is a two-part primary support bracket 3. The bracket is formed from two identical halves which come together to retain the main spindle bearing 27 and to support a drive spindle 1. The axis of the drive spindle 1 lies perpendicular to the axis of the central spindle 25. the drive spindle carries a pinion gear 2 between two cam assemblies 4, as shown in Figure 2. The central spindle has a gear rack profile 36 (see Figures 1 and 3) over part of its length, the rack engaging with the pinion gear 2. The lower end 37 of the central spindle is connected or fixed to a valve actuator shaft 38 by any suitable means, such as the connector 31 shown in Figure 1, so that linear axial movement of the central spindle results in linear axial movement of the valve actuator shaft. Furthermore, axial movement of the central spindle rotates the pinion, gear 2, and thus rotates the drive spindle 1 and cam assemblies 4.

Each cam assembly comprises a cam 39, a support hub 40 with a locking screw 41, a bellville disc spring or washer 42 and a circlip 43. The bellville washer 42 is pre-loaded by the circlip 43 to achieve a friction force between the cam 39 and the hub 40. This friction force should be sufficient to ensure that the cam will rotate with the hub and the drive spindle when in operation, but may still allow the cam to be rotated on the spindle to be set to the desired position for adjustment of the switching point. This arrangement for cam retention permits the user to set the cam positions without having to loosen and risk losing the fasteners in service or at the commissioning stage of the switch box.

The switch box of the present invention employs the rack and pinion principle to convert the linear action of the central spindle 25 and valve actuator 38 into rotary motion of the two independent switch-actuating cams 4. Each cam operates a limit switch 14, which may be either a mechanical switch or a proximity sensor which is activated as the rise of the cam presents metal to the sensing field, in order to provide an indication of the actuator and valve position. Normally, the open and closed positions of the valve require to be indicated; these positions generally occur at the two extremes of travel of the valve actuator, and hence of the central spindle.

The conversion of linear to rotary motion, and the actuation of limit switches or sensors 14 by means of rotating cams ensures that, regardless of the distance moved by the actuator or the setting of the switch, over- travel of the actuator shaft 38, central spindle 25 and drive spindle 1 will at no time result in excessive force being applied to the switch, which may cause premature failure of the assembly.

The switch box may be fitted to any one of a range of actuators with different stroke lengths. Maximum travel of the central and drive spindles and of the actuator shaft is limited by the length of the rack 36 on the central spindle. Within the housing terminal strips 19 and 24 an limit switches 14 are mounted on two plates 20 and 23 respectively, each plate being secured to the primary support bracket 3. Accordingly, this arrangement allows the manufacturer or user to fit any of a wide range of switch options within the housing, in order to cater for different application and market requirements. The suppo bracket 3 and plates 20 and 23 should be designed to ensu that, when fitted, the limit switch 14 is located in the optimum position for avoiding the possibility of incorrec assembly by the user.

The upper and lower housing sections 11 and 13 together provide a high degree of mechanical and environmental protection to the components housed therein An 0-ring seal 12 is located between the upper and lower housing sections 11 and 13 to provide a seal therebetween a further 0-ring seal 26 is positioned between the centra spindle 25 and the upper housing section 11, and another ring seal 28 is positioned between the central spindle an the lower housing section 13.

The lower section 13 has an aperture 42 over which a cover plate 22 is normally fitted, the plate containing apertures, such as threaded entries (not shown for the attachment of cable glands or conduits to the switch box. A sealing gasket 21 is located between the housing and the cover plate 22.

Two smaller bosses 43 with access holes may be formed in the lower section, one on either side. Such bosses may be provided with a cover 7 comprising either a blanking plate or a threaded conduit plate, which would facilitate the entry and glanding of electrical cables. sealing gasket 6 is fitted between each boss 43 and its cover 7. Since different covers may be fitted providing variety of thread options, this arrangement allows for considerable flexibility to meet different customers and market needs.

The lower housing section is provided with a downwardly extending skirt 44 which enables the switch box to be fitted, by fixing means 16 for example, to a mounting adapter 29. The skirt is formed with a circumferential groove 45, and fixing means 16 which may comprise one or more socket set screws are fitted through the wall of the adapter 29 to engage in the groove 45. The adapter 29 is inwardly flanged to be mounted on a valve bonnet by means of a screw fixing 18 the top 46 of the valve bonnet being shown schematically in Figure 1. The switch box, once located on the adapter may be rotated to its desired orientation relative to the actuator, the set screws 16 then being tightened to lock the assembly in place. This allows the user to position the switch box such that access to the cable entries may be made at any point through 360 degrees around the axis of the assembly. A sealing ring 17 is provided between, the skirt 44 and the adapter 29.

Different types of adapter may be used where the switch box is to be mounted on a different type of valve bonnet. One alternative adapter 32 is shown in Figure 4, where the adapter is flanged outwards and held on the valve bonnet 46 by fixing means 33.

In a preferred embodiment, the switch box of the present invention is intended to be used in conjunction with linear pneumatic valve actuators. Such devices are operated by means of a pneumatic signal normally controlled by a solenoid-operated pneumatic valve, either mounted on or remote from the actuator. For ease of installation and enhanced environmental protection, mounting of the solenoid control valve inside the switch box is advantageous. Figure 5 shows a pneumatic valve assembly with integral solenoid pilot control being provided as a sub-assembly 35 mounted in place of the cover plate 22 of Figures 1 and 2, the solenoids passing through the aperture 42 in the switch box housing. Additional terminals must then be provided on the terminal strips 19 and 24 into which the solenoid and the associated wiring is terminated. With the pneumatic valve assembly installed, one at least of the covers 7 on side bosses 43 must comprise a threaded conduit plate.

In addition to solenoid control, further ancillaries such as modulating control elements and digital communication devices may be fitted to the switch box in a similar way.

Claims

1. A valve switch box assembly comprising a valve spindle movable linearly between a first position and a second position in response to movement of an associated valve stem; at least one cam mounted in the switch box and mechanically coupled to the spindle for rotation by the spindle in response to linear movement of the spindle; and at least one micro-switch operable by the cam.

2. A valve switch box assembly according to claim 1 , wherein said at least one cam is mounted on a drive spindle, said drive spindle being oriented perpendicular to said valve spindle.

3. A valve switch box assembly according to claim 2, wherein a rack is provided on said valve spindle, said rack engaging with a pinion gear on said drive spindle.

4. A valve switch box assembly according to claim 2 or claim 3, wherein said at least one cam is mounted on said drive spindle so as to be rotatable with said drive spindle in operation of said valve switch box assembly, the position of said at least one cam on said drive spindle being rotatably adjustable.

5. A valve switch box assembly according to claim 4, wherein said at least one cam is mounted to rotate with said drive spindle in operation of said valve switch box assembly by means of friction between said at least one cam and said drive spindle.

6. A valve switch box assembly according to any preceding claim, further comprising a switch box housing and an adapter, said housing being mountable on said adapter and being rotatably adjustable with respect to said adapter.

7. A valve switch box assembly according to any preceding claim, further comprising a solenoid control valve.

R. A valve switch box assembly substantially as hereinbefore described with reference to the accompanying drawings.