AU783218B2 - Liquid level indicator guard - Google Patents

Description

I

P/00/0011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventor: Address for service in Australia: Invention Title: Gordon Brothers Industries Pty Ltd Graeme Jeffries CARTER SMITH BEADLE 2 Railway Parade Camberwell Victoria 3124 Australia LIQUID LEVEL INDICATOR GUARD Details ofAssociated Provisional Application.

PP7122 filed 13 November 1998 The following statement is a full description of this invention, including the best method of performing it known to us 2 LIQUID LEVEL INDICATOR GUARD This invention relates to guards for liquid level indicators and is particularly but not exclusively concerned with guards for liquid level indicators as used by the refrigeration industry.

Industrial refrigeration systems require liquid level indicators on various items of equipment, not only for the refrigerant, but also for lubrication oil. The most common type of liquid level indicator used in Australia is a column indicator between two points which provides a substantially continuous indication of the level of refrigerant between the points.

S 10 Column-type liquid level indicators conventionally utilise a glass tube mounted between upper and lower check valve assemblies connected to a refrigerant or oil vessel. The level of liquid in the glass tube corresponds to the level S:of liquid in the receiver or vessel. Whilst such devices operate effectively to indicate the level of liquid, the impact resistance of the glass tube is very low.

15 Although the check valves are designed to shut off automatically if the glass tube ooooo breaks, they may not totally prevent the release of refrigerant or oil in the event of breakage of the glass tube.

,.i In order to reduce the likelihood of accidental breakage of the glass tube, the column type liquid level indicators have previously been supplied with split tube guards of transparent plastics material which fit onto bosses at the ends of the glass tube. However, such removable plastics guards have not been widely accepted by the refrigeration industry, and it has been known for some users to fit two commercial angle iron sections as a guard around the glass tube, whilst leaving a gap for a person to inspect the level of refrigerant in the glass tube. Such angle iron sections may be detachably secured to the bosses at each end of the glass tube by worm drive hose clips. However, such angle iron sections are cumbersome and, due to their detachable nature, can easily be removed which defeats their purpose as permanent safety guards.

It is therefore desirable to provide a guard for a liquid level indicator which, once fitted around the glass tube, cannot be removed independently of the glass tube.

JRG:TOC:#29468.CAP 12 November 1999 It is also desirable to provide a guard for a liquid level indicator which provides better protection for the glass tube of the indicator than a removable plastics guard.

It is further desirable to provide an effective guard for a liquid level indicator which can be readily fitted to existing column-type liquid level indicators.

According to a first aspect of the present invention, there is provided a guard for a liquid level indicator having a glass tube mounted between upper and lower valve assemblies, wherein the guard comprises an elongate guard body at least part of which is adapted to surround the glass tube and having at least one opening for 10 viewing the level of liquid within the glass tube, and screw-threaded attachment •**°means provided at at least one end of the elongate guard body for attaching the elongate guard body to the liquid level indicator valve assembly, wherein the screwthreaded attachment means includes retaining means adapted to retain the .attachment means permanently to the elongate guard body.

Preferably, a screw-threaded attachment means is provided at each end of the elongate guard body for attachment to a respective valve assembly.

According to another aspect of the invention, there is provided a method of "*".*fitting a guard to a liquid level indicator of the column-type having a glass tube °adapted to be mounted between upper and lower valve assemblies, wherein the method includes the steps of: providing a guard having a hollow elongate guard body at least part of which is adapted to surround the glass tube of the liquid level indicator; the guard body having screw-threaded attachment members mounted to ends of the guard body; inserting the glass tube through the hollow guard body; inserting the ends of the glass tube into sealing glands of the valve assemblies; attaching the attachment members to complementary screw-threaded parts of the valve assemblies; JRG:TOC:#29468.CAP 12 November 1999 wherein the attachment members are permanently retained on the ends of the guard body, whereby the guard cannot be removed from the liquid level indicator without also removing the glass tube.

Each attachment means preferably comprises a screw threaded attachment member adapted to be fitted to a complementary threaded part of the liquid level indicator at an end of the glass tube of the indicator. In one preferred embodiment, the elongate guard body has a reduced diameter section and flange or collar of greater diameter at each end, and each screw threaded member is in the form of a nut received on the reduced diameter section and retained permanently thereon by a circlip located in an inaccessible groove in the nut.

The guard body may be of tubular form having a longitudinally extending through bore for receiving the glass tube of a liquid level indicator.

In another preferred embodiment, the guard body may be formed from one or more elongate body parts of substantially constant cross-section with collars of greater lateral dimension secured on each end of the body part or parts.

~In a particularly preferred embodiment, the guard body includes at least one heating element for heating the glass tube.

liquid level indicator guard in accordance with the invention is preferably of such dimensions that it can be retro-fitted to existing liquid level indicators to replace the removable or detachable metal or plastics types of guards presently in use. When the threaded nuts of the guard are fitted to the threaded parts of the valve assemblies at each end of the glass tube of the existing liquid level indicator, the circlips permanently located in the grooves in the nuts are engageable with the flanges or collars at the ends of the elongate guard body to prevent the guard being subsequently removed or detached without the glass tube also being removed.

According to a further aspect of the invention, there is provided a liquid level indicator of the column-type having a glass tube mounted between upper and lower valve assemblies, wherein the indicator includes a guard in accordance with the first aspect of the invention at least partially surrounding the glass tube and attached to parts of the valve assemblies by the attachment means.

JRG:TOC:#29468.CAP 12 November 1999 A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a sectional view through a liquid level indicator incorporating a known type of glass guard; Figure 2 is an enlarged section through the liquid level indicator of Figure 1; Figure 3 is an exploded perspective view of a guard for a liquid level indicator in accordance with the invention; Figure 4 is a side view of the guard body of the guard of Figure 3; Figure 5 is a section through the guard body; S 10 Figure 6 is a side view of one of the gland nuts of the guard of Figure 3; Figure 7 is a section on the line A-A of Figure 6; Figure 8 is an end view of the gland nut of Figure Figure 9 is a plan view of one of the retaining circlips of the guard of Figure 3.

15 Figure 10 is an exploded perspective view of a modified guard in accordance oo..o: with the invention; Figure 11 is a side view of the guard body of the guard of Figure "Figure 12 is a section through the guard body of the guard of Figure Figure 1 is a section through the guard body of gur of Figure and 12; Figure 13 is a section through the guard body of Figures 11 and 12; Figure 14 is a section through a modified guard body incorporating a heat trace element; Figure 15 is a plan view of an end collar of the guard body of Figure 14; Figure 16 is a horizontal section through one of the elongate body parts of the guard body of Figure 14; Figure 17 is an elevation of the body part of Figure 16; and Figure 18 is a vertical section through the body part of Figure 16.

Referring to Figures 1 and 2, there is shown a column-type liquid level indicator 1 for indicating the level of liquid in a high pressure liquid refrigerant or oil vessel 2 in a refrigeration system. The liquid level indicator 1 comprises a glass tube 3 mounted between upper and lower check valve assemblies 4 and JRG:TOC:#29468.CAP 12 November 1999 Each check valve assembly 4, 5 comprises a ball check valve 6, 7 within a hollow valve body 8, 9 that has a substantially horizontally extending portion 10, 11 adapted to be fitted to a respective part 12, 13 of the vessel 2 and a vertically extending portion 14, 15 adapted to receive a respective end of the glass tube 3.

The vertically extending portions 14, 15 of the valve bodies 8, 9 are of hollow cylindrical form, each having an internal bore 16, 17 and a screw-threaded external surface 18, 19.

A sealing gland 20, 21 is received in each internal bore 16, 17 into which a .eoe respective end of the glass tube 3 is inserted. Each sealing gland 20, 21 may .0 comprise a chevron seal 22, e.g. of sandwiched between gland rings 23, 24, e.g. of mild steel. Alternatively, the sealing glands 20, 21 may be O-ring seals.

The sealing glands 20, 21 are retained in position by gland nuts 25, 26 which are S'screwed onto the externally threaded vertically extending portions 14, 15 of the valve bodies 8, 9.

In use, liquid can flow from the receiver 2 past the ball check valves 6, 7 and into the glass tube 3 to indicate the level of liquid in the receiver 2. The ball check valves 6, 7 are designed so that they automatically shut off due to the pressure of S" refrigerant in the event of breakage of the glass tube 3. However, they do not S"totally prevent the release of liquid in the event of breakage of the glass tube 3.

Therefore, the liquid level indicator 1 is usually supplied with a removable plastics guard 27 for the glass tube 3. The removable plastics guard 27 is in the form of a split tube of clear plastics material, such as perspex, which slips onto machined boss portions 28, 29 of the gland nuts 25, 26. Each check valve assembly 4, 5 also includes a manually closable valve member 30, 31 connected by a rotatable spindle 32, 33 to a hand wheel 34, 35 for closing the check valve for replacement or maintenance of the glass tube 3 and/or glands 20, 21.

Referring to Figures 3 to 9, a guard for a column-type liquid level indicator as shown in Figures 1 and 2 comprises an elongate tubular guard body attachment means 50 in the form of upper and lower gland nuts 51, 52 for attaching each end of the guard body 40 to the respective vertically extending portions 14, of the valve bodies 8, 9 of the liquid level indicator 1, and retaining means 60 in the JRG:TOC:#29468.CAP 12 November 1999 form of circlips 61, 62 for retaining the gland nuts 51, 52 permanently on the guard body The elongate tubular guard body 40 is of stepped cylindrical form having a central guard portion 41, reduced diameter end portions 42, 43 and end flanges or collars 44, 45. The central guard portion 41 is formed with two elongate longitudinally extending openings 46 provided at diametrically opposed locations in the cylindrical guard portion. An axial bore 47 extends longitudinally through the V.0. elongate tubular guard body 40 for receiving the glass tube 3 of the liquid level indicator 1. The tubular guard body 40 is formed from a metal bar and preferably 10 from an aluminium extrusion which is machined to form the reduced diameter end portions 42, 43 and the openings 46.

A modified embodiment of a guard assembly is shown in Figures 10 to 13.

S:The modified guard assembly is similar to that of Figures 3 to 9 and corresponding reference numerals have been applied to corresponding parts. However, in the 15 modified embodiment, a guard body 70 is formed from two part-circular elongate ooeeo body parts 71, 72 of constant cross-section with an end collar 80 secured on each end of the body parts 71, 72. The body parts 71, 72 and collars 80 may be conveniently formed from aluminium extrusions. Each elongate body part 71, 72 oooo° has a part-circular outer surface 74 and an inner surface 75 having a central partcircular portion 76 between generally flat portions 77. Each end collar 80 has a cylindrical outer surface 81 and an opening 82 having sides of similar shape to the cross-sectional shape of the body parts 71, 72. The ends of the body parts 71, 72 are inserted into the opening 82 in respective collars 80 and secured thereto, e.g. by a force fit or by welds. In the assembled guard body 70, the inner surfaces 75 of the body parts 71, 72 face one another with the part-circular portions 76 being adapted to receive the glass tube 3 of a liquid level indicator 1 and a gap 78 between the inner surfaces 75 providing a slot for viewing the level of liquid in the glass tube.

Referring more particularly to Figures 3 and 6 to 8, each gland nut 51, 52 has a cylindrical portion 53 and a nut portion 54. The nut portion 54 has an internally screw-threaded bore 55 which is adapted to be screwed onto the screw-threaded external surface 18, 19 of a vertically extending portion 14, 15 of a respective one JRG:TOC:#29468.CAP 12 November 1999 8 of the valve bodies 8, 9. The nut portion 54 may be hexagonal in cross-section, or as shown in Figure 10, it may be part circular with flat surfaces on opposite sides.

A partition 56 extends across the interior of each gland nut 51, 52 between the cylindrical and nut portions 53, 54 for retaining the sealing gland 20, 21 of a respective valve body 8, 9 in position. The partition 56 has a central circular aperture 57 which allows the glass tube 3 of the liquid level indicator 1 to be inserted through the gland nut 51, 52. The cylindrical portion 53 of each gland nut 51, 52 has an annular groove 58 in its internal surface for receiving a respective circlip 61, 62. Circular openings 59 may be provided in the cylindrical portion 53 10 at diametrically opposed positions to allow viewing of the liquid level within the tube, thereby extending the effective viewing length of the assembly and to assist in the assembly (or disassembly) of the glass tube and guard between the valve assemblies. The gland nuts may be formed of any suitable metal, such as zincplated mild steel.

Each circlip 61, 62 comprises a generally C-shaped piece of spring metal forming an almost complete circular ring with a small gap 63 between the ends 64, of the circlip 61, 62. The circlip 61, 62 may be of square or rectangular crosssection. The external diameter of each circlip 61, 62 is such that it is adapted to be received snugly within the annular groove 58 of a respective gland nut 51, 52. The internal diameter of each circlip 61, 62 is slightly greater than the external diameter of the reduced diameter end portions 42, 43 of the tubular guard body 40 and less than the external diameter of the end flanges or collars 44, 45 of the guard body In assembly of the guard, each circlip 61, 62 is expanded and fitted over a respective end flange or collar 44, 45 onto a respective reduced diameter end portion 42, 43 of the guard body 40. The collars 44, 45 are provided with tapered annular surfaces 48 to assist in fitting the circlips 61, 62 over the collars 44, The cylindrical portion 53 of each gland nut 51, 52 is then moved over a respective collar 44, 45 and end portion 42, 43 of the guard body 40 so that a respective circlip 61, 62 is forced by engagement with a shoulder 49 between the central guard portion 41 and the respective reduced diameter portion 42, 43 into the annular groove 58 of the gland nut 51, 52. In order to facilitate installation of the circlips JRG:TOC:#29468.CAP 12 November 1999 61, 62 in the grooves 68 of the gland nuts 51, 52, the cylindrical portions 53 of the gland nuts 51, 52 may be provided with tapered or chamfered lead-in surfaces 69.

With the modified guard body 70 shown in Figures 10 to 12, after the circlips 61, 62 have been fitted over the end collars 80 onto the extruded body parts 71, 72, a special tool may be used to force the circlips 61, 62 into the grooves 58 in the gland nuts 51, 52. The end collars 80 may also be provided with tapered leading edges 85 to assist in fitting the circlips over the collars Once assembled on the guard body 40 or 70 the gland nuts 51, 52 are permanently retained on the reduced diameter portions 42, 43 of the body 40 or on *9 10 the body parts 71, 72 of the body 70 by the circlips 61, 62 which are trapped in the grooves 58 and which are engeable with the end flanges or collars 44, 45, 80 to prevent the gland nuts 51, 52 being removed from the guard body 40 or 70. In the captive circlip arrangement, the inside edge of the circlip 61, 62 may be visible in some instances, but since the circlip 61, 62 is eye-less and of rectangular or circular cross-section without a visible edge to pick up, it is non-removable.

The assembled guard as described above may be installed on a liquid level indicator 1 of the column-type of Figures 1 and 2 in the following manner.

.9 The glass tube 3 of the liquid level indicator 1 is inserted through the aperture 57 in one of the gland nuts 51, 52, into the guard body 40 or 70 and then through the aperture 57 in the other gland nut 52 or 51. One end of the glass tube 3, which is now surrounded by the guard body 40 or 70, is inserted at a slight angle into the sealing gland 20, 21 of the upper valve body 4. The recess in the upper valve body 4 for receiving the upper end of the glass tube 3 is deeper than that of the lower valve body 5 so that when the upper end of the glass tube 3 is inserted fully into the recess in the upper valve body 4, the lower end of the glass tube 3 can be moved laterally and then vertically down into the sealing gland 20, 21 of the lower valve body 5. The gland nuts 51, 52 are then screwed onto the screw-threaded external surfaces 18, 19 of the vertically extending portions 14, 15 of the respective upper and lower valve bodies 4, 5. It will be appreciated that although the gland nuts 51, 52 are permanently retained on the reduced diameter portions 42, 43 or on the body parts 71, 72 they can be moved longitudinally and rotated relative to the guard JRG:TOC:#29468.CAP 12 November 1999 body 40 or 70 to enable the guard body 40 or 70 and the glass tube 3 to be mounted between the valve bodies 4, In a fully assembled liquid level indicator 1 with the guard body 40 or surrounding the glass tube 3, it is impossible to remove the guard from the valve bodies 4, 5 without also removing the glass tube 3 at the same time. This is highly desirable and leads to additional safety, particularly for industrial refrigeration systems where it is not acceptable to have removable or detachable guards which can be removed from the liquid level indicator 1 whilst leaving the glass tube in position.

i 10 The present invention thus provides a guard for a liquid level indicator which e can be retro-fitted to existing column-type indicators, such as described above with reference to Figures 1 and 2. Alternatively, or additionally, a column-type liquid level indicator may be manufactured as a new item with a guard as described above pre-fitted to surround the glass tube. In each case, in the fully installed indicator and guard assembly, the guard cannot be removed without also removing the glass tube of the indicator.

The modified form of guard body 70 illustrated in Figures 10 to 12 has .i advantages over that of Figures 4 and 5 in retro-fitting to existing liquid level indicators in that an installer can take all the parts separately to the site where the liquid level indicator is installed, the extruded body parts 71, 72 of constant crosssection can be cut to the required length, the collars 80 welded to the body parts 71, 72 and then the circlips 61, 62 and captive gland nuts 51, 52 fitted onto the guard body 70. This avoids taking measurements of the liquid level indicator on site, having the guard body 40 made in a machine shop environment and returning to site to fit the guard.

In a further embodiment of the invention illustrated in Figures 14 to 17, the elongate parts 71, 72 of the guard body 70 may be modified to incorporate one or more heating elements 90 for heating the glass tube 3 of the liquid level indicator guard. As shown in Figures 14 to 18, the inner surfaces 75 of the body parts 71, 72 have a longitudinally extending central groove or channel 176 between slightly inclined flat surfaces 177. The grooves or channels 176, are adapted to receive JRG:TOC:#29468.CAP 12 November 1999 11 heating elements in the form of heat tracer strips 90 extending longitudinally along the grooves or channels 176 and connected by electrical wires 92 to an electrical power source. As shown in Figures 17 and 18 a hole or slot 94 is drilled or machined in one end of the extruded elongate part 71 of the guard body 70 to enable the heat tracer strip 90 to be inserted into the groove or channel 176 and the other end of the elongate part 71 may have a recess 96 provided therein for receiving the termination end 98 of the heat tracer strip 90. Alternatively, holes or slots 94 may be provided in both ends of the body part 71 for installation of the heat tracer strip 90. In one preferred embodiment, the slots 94 are inclined at an angle, eg. 450, towards the centre of the guard to facilitate easier heat tracer installation.

Heat tracing is desirable in applications where the temperature around the sight glass may be lower than the temperature of the fluid inside the vessel to which the sight glass is fitted. Whilst this is not an issue for single phase fluids, many of the liquid level indicators to which the guards are fitted are used to measure the oil 15 level in refrigeration compressor oil separators, with ammonia vapour above the oil oo,.o: level in the vessel. Hence, if the sight glass is colder, the ammonia vapour condenses on top of the oil in the sight glass, giving misleading levels, and often the S- perception is that the oil separator has in fact got a layer of liquid ammonia on top of the oil surface, and the related fear is that lubricity may be lost if the ammonia is picked up in the oil pump from the oil separator. Therefore, by heating the sight glass, the condensation is prevented.

In the guard body shown in Figure 14 the heat tracer strip 90 is in tangential contact with the glass tube 3. In this arrangement, the heat tracer strip 90 heats the extruded metal guard body part 71 so that the body part radiates heat onto the glass tube 3, in addition to heating by conduction via tangential contact with the glass tube 3.

Whilst in many applications, one heat tracer strip may provide sufficient heating of the glass tube 3, in some applications, heat tracer strips 90 may be provided in grooves or channels 176 in both body parts 71, 72 of the guard body It will be appreciated that various modifications and additions may be made to the preferred embodiments described above without departing from the scope and JRG:TOC:#29468.CAP 12 November 1999 12 spirit of the present invention. For instance, the guard may include a level scale to be inserted behind the glass tube on assembly/installation.

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Claims (18)

1. A guard for a liquid level indicator having a glass tube mounted between upper and lower valve assemblies, wherein the guard comprises an elongate guard body at least part of which is adapted to surround the glass tube and having at least one opening for viewing the level of liquid within the glass tube, and screw- threaded attachment means provided at at least one end of the elongate guard body for attaching the guard body to a liquid level indicator valve assembly, wherein the screw-threaded attachment means includes retaining means adapted to retain the 10 attachment means permanently to the elongate guard body.

2. A guard according to claim 1 wherein at least one end of the elongate guard body has a flange or collar of greater lateral dimension than an adjacent part of the guard body, and the attachment means at that end of the guard body comprises a 15 screw-threaded member adapted to be fitted to a complementary threaded part of oo.ooi the liquid level indicator.

3. A guard according to claim 2 wherein the screw-threaded member is received on the guard body and retained permanently thereon by a circlip located in a groove in the screw-threaded member and engageable with the flange or collar of the guard body.

4. A guard according to claim 3 wherein the location of the groove in the screw-threaded member and the dimensions of the circlip are such that, once fitted in the groove, the circlip is substantially non-removable from the groove. A guard according to claim 3 or claim 4 wherein the screw-threaded member comprises a gland nut having a nut portion with an internally screw-threaded bore and a cylindrical portion having an annular groove in its internal surface for receiving said circlip.

JRG:TOC:#29468.CAP 12 November 1999 14

6. A guard according to claim 5 wherein openings are provided in the cylindrical portion of the screw-threaded member at diametrically opposed positions.

7. A guard according to any one of claims 3 to 6 wherein the circlip comprises an almost complete ring of spring metal having a small gap between its ends.

8. A guard according to claim 7 wherein the circlip is of square or rectangular eeoo "-cross-section.

9. A guard according to any one of the preceding claims wherein the guard body includes at least one heating element for heating the glass tube.

10. A guard according to any one of the preceding claims wherein the guard 15 body comprises a pair of elongate body parts with end collars secured on the ends of the body parts.

11. A guard according to claim 10 wherein the elongate body parts are spaced from each other to define a gap therebetween for viewing the level of liquid in the glass tube partially surrounded by the elongate body parts.

12. A guard according to claim 10 wherein the elongate body parts have inner surfaces which face each other and which, in the assembled guard, are disposed on opposite sides of the glass tube.

13. A guard according to claim 12 wherein the inner surface of at least one of the elongate body parts has a groove or channel for receiving a heat tracer strip for heating the glass tube.

14. A guard according to any one of claims 10 to 13 wherein the elongate body parts of the guard are formed from aluminium extrusions.

JRG:TOC:#29468.CAP 12 November 1999 A guard according to any one of claims 1 to 9 wherein the guard body is formed from a tubular metal bar which is machined to form reduced diameter end portions adjacent end flanges.

16. A guard according to claim 15 wherein two elongate openings are provided in opposite sides of the guard body for viewing the level of liquid in the glass tube. s*

17. A liquid level indicator having a glass tube mounted between upper and i:0.00 10 lower valve assemblies, including a guard in accordance with any one of the preceding claims at least partially surrounding the glass tube and attached to parts of .00 the valve assemblies by the screw-threaded attachment means.

18. A method of fitting a guard to a liquid level indicator of the column-type 15 having a glass tube adapted to be mounted between upper and lower valve assemblies, wherein the method includes the steps of: providing a guard having a hollow elongate guard body at least part of which S.o. is adapted to surround the glass tube of the liquid level indicator; S" the guard body having screw-threaded attachment members mounted to ends of the guard body; inserting the glass tube through the hollow guard body; inserting the ends of the glass tube into sealing glands of the valve assemblies; attaching the attachment members to complementary screw-threaded parts of the valve assemblies; JRG:TOC:#29468.CAP 12 November 1999 wherein the attachment members are permanently retained on the ends of the guard body, whereby the guard cannot be removed from the liquid level indicator without also removing the glass tube. DATED: 12 November, 1999 CARTER SMITH BEADLE Patent Attorneys for the Applicant: 10 GORDON BROTHERS INDUSTRIES PTY LTD S o o S JRG:TOC:#29468.CAP 12 November 1999