AU617512B2 - Valve Device - Google Patents

Description

AUSTRALIA

Patents Act 6 g COMPLETE SPECIFICATION

(ORIGINAL)

Class Application Number: Lodged: Int. Class Complete Specification Lodged: Accepted: Published: Priority Related Art: 41 4 1 i 44 4 4 i 4 4 1 Name(s) of Applicant(s): Address(es) of Applicant(s): Actual Inventor(s): APPLICANT'S REF.: VALVE DEVICE JOHN STANLEY MELBOURNE 10 Dellas Avenue Templestowe, Victoria 3106

AUSTRALIA

JOHN STANLEY MELBOURNE Address for Service is: PHILLIPS, ORMONDE AND FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne, Australia, 3000 o 2827 240869 Complete Specification for the invention entitled: VALVE DEVICE The following statement is a full description of this invention, including the best method of performing it known to applicant(s): P19/3/4 i This invention relates to an improved valve stem for a soft-seated spool valve, and to an improved fluid control device comprising a soft-seated spool valve having such valve stem.

One form of fluid control soft-seated spool valve device in wide use has an elongate housing in which an elongate valve stem is movable longitudinally to control fluid flow between two or more ports in the body. The stem may be movable in a number of ways, such as manually, mechanically, pneumatically or the like. In such devices, the valve stem has at least one undercut portion of reduced diameter, with such portion being positionable relative to valve sealing members mounted within the housing, by movement of the stem, to provide communication between selected ports. The sealing members are provided with sealing bushes, such as of Teflon, which seal against the main surface of the stem, to either side of the undercut portion.

In the devices of the above type, the transitions from the main surface of the stem to the lesser diameter of the undercut portion is relatively sharp. Thus, while shoulders between the main surface and the undercut portion may be slightly rounded adjacent the main surface, the shoulders extend substantially radially or at a relatively small angle to a radial plane.

The present invention provides a valve stem for a fluid control, soft-seated spool valve, said valve stem comprising a main peripheral surface and at least one undercut portion, the undercut portion at each end thereof being axially spaced from, and merging with, the main surface of the stem by means of respective shoulder which provides a smooth transition from the main surface to the undercut portion; wherein each shoulder curves smoothly from the main surface such that, viewed in an axial section of the stem, the shoulder has a convex radially outer portion; and wherein each shoulder has an extent axially of the stem, from the main surface to the undercut portion, along which its radius decreases smoothly and without a step-wise reduction in radius.

-2- Each shoulder preferably is such that, viewed in the axial section, the shoulder has a concave, radially inner portion. The radially outer portion preferably has a radius of curvature Rc which is large relative to the transverse cross-sectional radius R of the main surface.

The ratio of Rc to R preferably is in the range of from 0.75:1 to 3:1, such as from about 1:1 to 2:1.

The shoulder may curve smoothly from the radially outer to the radially inner portions thereof such that, when viewed in section, there is a point of inflection between those portions. However, the shoulders of course are of annular form 3A -2a- 1054L when viewed axially and the change in curvature occurs around a circumferential line of inflection.

The line of inflection preferably is on a circle having a radius approximately equal to the average of the transverse cross-sectional radii of the main surface and the undercut portion. However, the radius of the circle may exceed such average by up to about 10% of the difference in radius between the main surface and the undercut portion. Such variation most preferably is not more than 5% of that difference. However, the line of inflection may have a radius substantially less than the average of the radii of the main surface and Lhe undercut portion; the line of inflection having a radius of, for example, up to 30% less than such difference.

It is found that a valve device having a valve stem according to the invention can achieve significant improvement over prior devices. Thus, rather than necessitating use of relatively soft Teflon bushes, the stem of the invention can use bushes of harder materials such as carbon or molybdenum disulphide filled PTFE or Delrin. With such harder bushes, the rating of the valve device can be increased from a level of about 2000 KPa for a conventional device with Teflon bushes, to a rating of about 20,000 KPa. Alternatively, a device according to the invention can be used at a lower rating to achieve a significantly enhanced operating life.

0 In order that the invention may more readily be understood, reference now is directed to the accompanying drawings in which: Figure 1 shows fluid control components of a valve device according to the invention; and Figure 2 shows detail of the valve stem of Figure 1.

In the drawings, device 10 is a three-way valve. Device has a hollow, elongate body 12 in which a valve stem 14 is longitudinally slidable to control fluid flow between a selected one of ports 16,17 and port 18. Stem 14 is movable either manually, or by conventional mechanical, pneumatic, or other means against the bias of spring 19 which normally biases stem 14 to the left. Within bore 20 of housing 12, a respective one of valve members 22,24 is mounted across each of 39 respective passageways 26,27 of ports 16,17 such that, with JW -3i: Imovement of stem 14, one of passageways 26,27 communicates with passageway 28 of port 18. Each of members 22,24 comprises a cage 30, such as of brass, stainless steel or plastics, and a pair of bushes 32 which sealingly engage stem 14 and have encircling, resilient O-rings 34 which seal against bore Stem 14 is of circular cross-section and has a main external surface 36 of radius R in which is formed an undercut portion 38 of lesser radius At each end of portion 38, surface 36 merges therewith via a smooth shoulder 40. Extending from surface 36, each shoulder has a radially outer convex portion 42 which merges smoothly with a radially inner concave portion 44. The latter portion merges smoothly with the reduced diameter surface of portion 38; the latter being of circular section.

Shoulder portion 42 has a relatively large radius of curvature Rc; that radius being slightly greater than the radius R of stem 14 at surface 36. The ratio of Rc to R can range from 0.75:1 to 3:1, such as from 1:1 to 2:1. Portion 42 merges with portion 44 at a circular line of inflection, at which the direction of curvature changes. That circle has a radius approximately equal to the average of the radii of stem 14 at surface 36 and at portion 38, i.e. the average of R and although the radius of circle C can range from slightly greater than to substantially less than that average as detailed herein.

Stem 14 is movable axially within housing 12 to provide communication between a selected one of ports 16,17 and port 18. Cages 30 are open such that fluid flow between the selected one of ports 16,17 and port 18 passes therethrough; with a seal against stem 14 being provided by the respective bushes 32. In the arrangement shown, stem 14 is shown almost at its left hand extreme position to enable flow between ports 16,18 via passageways 26,27, with flow via passageways 28,29 being blocked by surface 36 of stem 14.

Stem 14 enables attainment of advantages as previously detailed herein. It also is able to move smoothly in housing 12, due to shoulders 40 providing a positive centering action on bushes 32, thereby accommodating variations in manufacturing -12- tolerances for bushes 32 or their wear in use.

-4- Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.

t it 1 1 I t 14 39 JW

Claims (12)

1. A valve stem for a fluid control, soft-seated spool valve, said valve stem comprising a main peripheral surface and at least one undercut portion, the undercut portion at each end thereof being axially spaced from, and merging with, the main surface of the stem by means of respective shoulder which provides a smooth transition from the main surface to the undercut portion; wherein each shoulder curves smoothly from the main surface such that, viewed in an axial section of the stem, the shoulder has a convex radially outer portion; and wherein each shoulder has an extent axially of the stem, from the main surface to the undercut portion, along which its radius decreases smoothly and without a step-wise reduction in radius.

2. A valve stem according to claim 1, wherein each shoulder is such that, viewed in said axial section, the shoulder has a concave, radially inner portion.

3. A valve stem according to claim 2, wherein the radially outer portions have a radius of curvature Rc which is large relative to the transverse cross-sectional radius R of the main surface.

4. A valve stem according to claim 3, wherein the ratio of Rc to R is in the range of from 0.75:1 to 3:1.

5. A valve stem according to claim 3, wherein the ratio of R to R is in the range of from 1:1 to 2:1. c

6. A valve stem according to any one of claims 2 to wherein a change in curvature from a radially outer portion to a respective radially inner portion occurs around a circumferential line of inflection.

7. A valve stem according to claim 6, wherein the line of inflection is on a circle having a radius approximately equal to the average of the transverse cross-sectional radius of the main surface and the transverse cross- sectional radius of the undercut portion.

8. A valve stem according to claim 6, wherein the line of inflection is on a circle having a radius which exceeds the average of the transverse cross-sectional radius of the main surface and the transverse cross-sectional radius "'V 4 054L -6- i- 1 31 nps of the undercut portion by up to about 10% of the difference in radius of the main surface and undercut portion.

9. A valve stem according to claim 6, wherein the line of inflection is on a circle having a radius which is less than the average of the transverse cross-sectional radius of the main surface and the transverse cross-sectional radius of the undercut portion by up to about 30% of the difference in radius of the main surface and undercut portion.

A fluid control device, comprising a soft-seated spool valve having a valve stem in accordance with any one of claims 1 to 9.

11. A valve stem according to claim 1, substantially as 15 herein described with reference to the accompanying drawings.

12. A fluid control valve device according to claim substantially as herein described with reference to Figure i, i 1. 20 DATED: 23 August 1991 PHILLIPS ORMONDE FITZPATRICK Attorneys for: JOHN STANLEY MELBOURNE 0* *0 a: -7- 1054L