US3625390A

US3625390A - Sight glass assembly

Info

Publication number: US3625390A
Application number: US704368A
Authority: US
Inventors: Charles E Meginnis
Original assignee: Individual
Current assignee: PRESSURE PRODUCTS COMPANY Inc A CORP OF WEST VA
Priority date: 1968-02-09
Filing date: 1968-02-09
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07
Also published as: FR1568477A; DE1750556B2; JPS4835809B1; GB1202103A; DE1750556A1; DE1750556C3

Abstract

A sight glass assembly comprising housing means having an opening therethrough, a lens mounted in the opening, the opening having an inclined wall, resilient packing means interposed between the lens and the inclined wall of the opening, a faceplate disposed about the lower periphery of the lens engageable with the packing member and means for securing the faceplate to the housing means to apply a force on the packing means directed against the inclined wall of the opening in the housing means whereby the packing means is forced toward the lens to provide a compressive force about the periphery thereof.

Description

United States Patent [72] Inventor Charles E. Meginnis FOREIGN PATENTS 222 Nancy Charlesm"! W 460,970 2/1937 Great Britain 220/46 [211 Appl 704,368 Primary ExaminerGeorge E. Lowrance [22] Filed 9 9 An0rneyMason, Fenwick & Lawrence [45] Patented Dec. 7, 1971 ABSTRACT: A sight glass assembly comprising housing [54] SIGHT GLASS ASSEMBLY means having an opening theret hrough, a lens mounted in the 17 Claims 5 Drawing Figs opening. the opening having an inclined wall, resilient packing means interposed between the lens and the inclined wall ofthe [S2] U.S. Cl 220/46 R, Opening a f late di d b ut the lower periphery ofthe 73/334 220/82 R lens engageable with the packing member and means for [51] Int. Cl B65d 53/06 Securing the faceplate to h housing means to apply a force [50] Field of Search... 220/46, 81, on the packing means directed against h inclined l ofthe 8] 82 R; 73/334- 33] opening in the housing means whereby the packing means is forced toward the lens to provide a corn ressive force about [56] References Clted p UNITED STATES PATENTS the periphery thereof 3,307,400 3/1967 LeRoy 73/33l l l l PATENTEDDEC 71ml 3.625390 SHEET 1 [IF 2 33 I 5 /////7 m i INVENTOR 6/4 245s /Vevnwwa mam im m Wm ATTORNEYS PATENTED DEC 1 l97| 3,525,390

sum 2 0f 2 I i I SAi mvsm og 6 /4 245: 5 Msv/mws BY 3% O9 mosey, 04mm ATTORNEYS SIGHT GLASS ASSEMBLY This invention relates to a sight glass assembly, and more particularly to a sight glass assembly suitable for use with highpressure vessels.

In the prior art there has been developed a type of sight glass assembly which generally includes a housing member having an opening therethrough, which is adapted to be mounted across an opening in a pressure vessel, a lens mounted in the opening of the housing member and a packing member mounted in the opening inthe housing member between the wall of the opening in the housing member and the periphery of the lens. In this general type of sight glass assembly it has been found that the principal source of failure resides in leakage of the medium in the pressure vessel through the assembly between the packing member and the lens. It, therefore, has been found desirable in the art to provide a sight glass assembly, of the general type described, which would materially reduce and preferably eliminate the above-mentioned source of failure.

Accordingly, it is the principal object of the present invention to provide an improved sight glass assembly.

Another object of the invention is to provide an improved sight glass assembly of the type having a lens mounted in a metal housing structure, wherein effective scaling is provided between the lens and the housing structure.

A further object of this invention is to provide an improved sight glass assembly mountable on a vessel containing a fluid under pressure, having primary and secondary sealing means to prevent leakage of the fluid through the assembly.

A still further object of this invention is to provide a novel sight glass assembly suitable for use with high-pressure vessels wherein the lens thereof is maintained in radial compression, thus preventing blowout of the lens under normal operating conditions.

Another object of this invention is to provide an improved sight glass assembly for vessels containing corrosive mediums, wherein the sealing means of the assembly is protected from the corrosive medium.

A further object of the present invention is to provide a novel lens unit for a sight glass assembly.

A still further object of the present invention is to provide an improved sight glass assembly for pressure vessels, which is comparatively simple in construction, relatively easy to assemble and disassemble and inexpensive to manufacture.

Other objects of the present invention will become more apparent to those persons skilled in the art, from the following description when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a top plan view of an embodiment of the invention;

FIG. 2 is an exploded perspective view of the embodiment illustrated in FIG. 1;

FIG. 3 is an enlarged cross-sectional view taken along line 3-3 in FIG. 1;

FIG. 4 is an exploded view of another embodiment of the invention illustrated in vertical cross section; and

FIG. 5 is an enlarged assembled view of the embodiment illustrated in FIG. 4, illustrating the components in vertical cross section.

Briefly described, the present invention relates to a sight glass assembly generally comprising a housing means having an opening therethrough, a lens mounted in the opening, the opening having a peripheral wall inclined away from and in opposed relation to the periphery of the lens, packing means consisting of a resilient material interposed between the periphery of the lens and the inclined wall of the opening in the housing means, a faceplate disposed about the lower periphery of the lens engaging the packing means, and means of securing the faceplate to the housing means to apply a force on the packing means directed against the inclined wall of the opening in the housing means, whereby the packing means is forced toward the lens to provide a compressive force about the periphery of the lens and opposing the force of the pressure within the vessel on which the assembly is adapted to be mounted. Preferably, the packing means is adhesively secured to the lens and the faceplate.

According to a more specific embodiment of the invention, there is provided a sight glass assembly comprising a housing means having a circular opening therethrough. Mounted in the opening is a circular lens. The opening in the housing member is provided with a peripheral wall which is substantially frustoconical in shape and disposed in opposed relation to the periphery of the lens. Packing means consisting of a resilient material, is interposed between the periphery of the lens and the frustoconically shaped wall of the opening. An annular faceplate is mounted about the lower periphery of the lens engaging the packing mans, which is secured to the housing means about its circumference to apply a force on the packing means directed against the inclined wall of the opening in the housing means, whereby the packing means is forced toward the lens to provide a compressive radial component of force about the periphery of the lens and an axial component of force opposing the force developed by the pressure in the vessel. Preferably, the housing structure is provided with an annular beveled surface adjacent the opening therein and opposed to the faceplate, which is adapted to receive therebetween an annular flange portion of the packing means, which is compressed when the faceplate is secured to the housing means. In addition, the packing means is adhesively secured to the lens and the faceplate.

Referring to FIGS. 1 through 3 of the drawings, there is illustrated an embodiment of the invention. FIG. 1 illustrates a sight glass assembly 10, which is adapted to be rigidly secured to a vessel or container 11 containing, perhaps, a fluid under pressure. As best shown in FIG. 2, the assembly includes a housing member 12, a lens 13, upper and lower cushioning gaskets 14 and 15 (not shown in FIG. 2), a packing member 16 and a faceplate 17. The entire assembly is adapted to be mounted on the pressure vessel 11 across a circular opening 18, as illustrated in FIG. 3.

The housing member 12 is substantially annular, having parallel upper and lower

annular surfaces

19 and 20. The lower surface 20 is adapted to be disposed adjacent the wall of the pressure vessel. The housing structure is provided with a plurality of circumferentially spaced openings 21 for receiving bolts 22 therethrough, for rigidly securing the sight glass assembly to the wall of the pressure vessel.

Leakage between the wall of the pressure vessel and the sight glass assembly is prevented by means of an annular sealing gasket 23 disposed between the bottom surface of faceplate 17 and an annular recess 32 formed in the wall of the pressure vessel.

The housing structure also is provided with a circular opening 24 therein. The upper end of the opening 24 is beveled as at 25, and the opening is enlarged, as at 26, to provide an annular shoulder 27. Below the enlarged opening 27, the opening is enlarged further, and is provided with a frustoconically shaped wall 28. The lower end of the opening also is provided with an annular beveled surface 29, which is curved upwardly at its inner end to merge into the frustoconically shaped wall 28. Seated on the annular shoulder 28 is the upper gasket 14 which is engaged by the lens 13. The lens 13 is cylindrical in shape and is provided with a cylindrical wall 30, which is spaced from the frustoconically shaped wall 29 of the opening in the housing member. Interposed between the wall 28 and the cylindrical surface 30 of the lens is the packing member 16. The packing member is formed from a resilient material which is premolded. The packing member includes an integral annular flange portion 31 at its lower end, which engages the annular beveled surface 29 of the housing member.

Mounted on the packing member 16, including the annular flange portion 31 thereof, is the faceplate 17. The faceplate 17 is annular, having an outside diameter substantially equal to the outside diameter of the beveled surface 29 of the housing member and an inside diameter slightly less than the diameter of lens 13. The upper inner portion of the faceplate 17 is recessed to receive the lower annular gasket 14 which is interposed between the faceplate and the lens. As best illustrated in FIG. 3, when the sight glass assembly is mounted on the wall of the pressure vessel, the faceplate 17 secured to the housing member, is received within annular recess 32 provided in the outer surface of the wall member of the pressure vessel, and about the periphery of the opening 18 therein.

The faceplate is secured to the housing member by means of a plurality of flat head screws 33, which are circumferentially spaced about the faceplate. Upon tightening the screws 34 about the circumference of the faceplate 17, the annular flange portion 31 of the packing member is compressed to form a seal between the faceplate 17 and the housing member 12. In addition, the main body of the packing member 16 is forced against the frustoconically shaped wall 28, to produce a radially directed compressive force against the cylindrical wall 30 of the lens. This action provides a fluidtight seal between the housing structure and the lens, and furthermore, places the lens 13 in radial compression. The radial compression of the lens results in an important safety feature, in that it substantially decreases the chances of blowout of the lens.

The packing member 16 preferably is formed from a resilient adhesive material such as silicone rubber, which is premolded and adheres to the cylindrical surface 30 of the lens and the upper surface of the faceplate 17.

The faceplate 17, lower gasket IS, lens 13 and packing member 16 are formed as an integral unit. In fabricating the unit, in one embodiment, the gasket 15 is positioned in the annular recess of the faceplate, the lens is mounted on the gasket 15 and then the packing member consisting of an uncured adhesive silicone rubber is mounted on the faceplate and lens and adheres thereto. The packing member is then cured to complete the unit, whereby the packing member will be firmly adhered to the lens and faceplate.

It will be appreciated that the adhesive engagement of the packing member 16 with the components of the assembly provides a primary sealing means between the lens and the packing member, to prevent leakage of the medium contained in the vessel 11. In addition, the pressure applied by tightening the screws 33 forces the packing member against the frustoconically shaped wall 28, producing a radial inward compressive force about the periphery of the lens to provide a secondary sealing action between the housing member and the lens.

The housing structure and the faceplate may be constructed of any suitable material, although metallic materials are preferred. The plate member 17, furthermore, preferably is formed of a corrosive resistant material such as stainless steel. The housing structure can be constructed of any material having suitable strength characteristics. It is not necessary that the housing structure by constructed of a corrosive resistant material, in that it is not exposed readily accessible to the fluids contained within the pressure vessel.

The lens 13 is prevented from being placed in tension when the bolts 22 are tightened by means of the limit of travel of the housing member relative to the annular plate 17. The entire assembly can be removed from the vessel, merely by removing the bolts 22.

The packing member 16 can be made of a sufficient axial dimension so that before the faceplate is placed in position and secured to the housing member, the packing member will extend beyond the surface of the housing member.

FIGS. 4 and 5 illustrate another embodiment of the invention, which particularly is adapted for use when a corrosive medium is contained within the pressure vessel. This embodiment includes a housing member 34, a packing member 35, a protective liner member 36, a lens 37, upper and

lower cushioning gaskets

38 and 39, and a faceplate member 40. As illustrated in FIG. 5, the second embodiment of the sight glass assembly is adapted to be mounted on a pressure vessel 41, having a circular opening 43 therein. The housing member 34 is similar to the housing member described in connection with the first embodiment, including parallel upper and lower

annular surfaces

43 and 44. The lower surface 44 is adapted to be mounted adjacent the wall of the pressure vessel 41 in the manner illustrated in FIG. 5. The housing member 34 also is provided with a plurality of circumferentially spaced openings 45, which are adapted to receive a plurality of bolts 46 for securing the housing member to the wall of the pressure vessel. Leakage between the sight glass assembly and the wall of the pressure vessel is prevented by means of a suitable annular sealing gasket 47.

The housing member is provided with a circular opening 48 therethrough, having an upper beveled wall 49. The lower portion of the opening 48 is enlarged as at 50, to provide an annular shoulder 50a and to a greater extent therebelow to provide a frustoconically shaped wall 51. The lower surface 44 of the housing member about the opening therein is provided with an annular beveled surface 52 which is curved inwardly and upwardly toward the inner end thereof to merge with the frustoconically shaped wall 51.

Mountable within the opening of the housing structure is the packing member 35 which is formed from a resilient material, as in the case of the packing member described with the first-mentioned embodiment. The packing member includes an annular flange portion 53, the upper surface of which engages the beveled surface 52 on the housing member when the packing member is inserted in the opening therein. The packing member 35 is protected from any corrosive mediums within the pressure vessel by means of the liner member 36. The liner member includes a cylindrical portion 54 which is received within the opening in the packing member, and an annular outwardly projecting flange portion 55 which engages the lower surface of the packing member including the annular flange portion 53 thereof. It will be seen in FIG. 5 that the packing member 35 is completely enclosed and protected by the liner member 36. The liner member is made relatively thin and is formed from any suitable flexible material which has corrosive resistant properties.

The faceplate 40 is substantially annular, having an outside diameter greater than the beveled surface 52 of the housing member and an inside diameter slightly less than the outside diameter of the lens 37. The upper inner end of the faceplate member is annularly recessed to provide a space for the lower annular cushioning gasket 39. The lens 37 has an outside diameter slightly less than the annular recess in the faceplate member, so that there may be provided an annular seal 56 between the lens and the faceplate member. The lens is secured to the faceplate member with the lower cushioning gasket 39 interposed between the lower surface of the lens and the faceplate member, by means of the seal 56 which also is formed from a resilient material.

With the lens mounted on the faceplate member, as illustrated in FIG. 4, the entire unit can be inserted into the opening in the housing member so that the upper annular cushioning gasket 38 engages annular shoulder 500, the cylindrical surface of the lens 37 is received within and engages the cylindrical portion 54 of the liner member, and the faceplate member 40 engages the annular flange portion 55 of the liner member. The faceplate member is secured to the housing structure by means of a plurality of circumferentially spaced, flat head screws 57 as best seen in FIG. 5. When the sight glass assembly is mounted on the pressure vessel, the faceplate 40 is received within an annular recess 58 formed in the outer surface of the wall 41 of the pressure vessel and seated on gasket 47 about the periphery of the opening 42 therein.

In the embodiment illustrated in FIGS. 4 and 5, a primary seal between the faceplate member and the lens is provided by the seal 56. In addition, a secondary seal is provided when the screws 57 are tightened to compress the annular flange portion 53 of of the packing member and to force the main body of the packing member against the frustoconically shaped wall 51, to produce a compressive radial force against the lens 37. In this embodiment, primary and secondary seals are provided, and the packing member is protected from the corrosive effects of the medium within the pressure vessel by means of the liner member 36. In addition, it will be noted that the limit of travel of the housing member relative to the annular force plate member 40 prevents the lens from being placed in tension when the screws 57 are tightened to firmly secure the faceplate member to the housing member. As mentioned in connection with the first embodiment. The faceplate member and the housing member can be formed of any suitable rigid materials, although metallic material are preferred. Furthermore, it is preferred that the faceplate member be constructed of a corrosive resistant material such as stainless steel, considering that the faceplate member constantly is exposed to the interior of the pressure vessel. The housing structure, however, need not be constructed of a corrosive resistant material, in that it is not exposed or readily accessible to fluids contained within the pressure vessel. The liner member is formed from a chemical and heat resistant, flexible material, such as Teflon.

In both of the above-described embodiments, it will be appreciated that effective sealing means are provided to prevent leakage of the medium within the pressure vessel between the lens and the housing member. In addition, the lens is placed under a compressive radial load which is effective in preventing the lens from blowing out, thereby providing an additional safety feature for the assembly.

From the foregoing detailed description it will be evident that there are a number of changes, adaptations and modifications of the present invention which come within the province of those skilled in the art. HOwever, it is intended that all such variations not departing from the spirit of the invention be considered as within the scope thereof as limited solely by the appended claims.

lclaim:

l. A sight glass assembly comprising housing means having an outer side, an inner side mountable on a vessel wall having an opening therein and an opening therethrough registrable with the opening in said wall when said housing means is mounted on said wall, a lens having outer and inner sides mounted in said opening of said housing housing means, said opening in said housing means having a peripheral wall inclined away from and in opposed relation to the periphery of said lens, packing means consisting of a resilient material interposed between the periphery of said lens and the inclined wall of the opening in said housing means, a faceplate disposed about the inner periphery of said lens engaging said packing means and means for securing said faceplate to the inner side of said housing means to apply a force on said packing means directed against said inclined wall whereby the packing means is forced toward said lens to provide a compressive force about the periphery thereof.

2. A sight glass assembly according to claim 1, wherein the lens is circular, the inclined wall is frustoconical and the faceplate is annular.

3. A sight glass assembly comprising housing means having an opening therethrough, a lens mounted in said opening, said opening having a peripheral wall inclined away from and in opposed relation to the periphery of said lens, packing means consisting of a resilient material interposed between the periphery of said lens of the inclined wall of the opening in said housing means, a faceplate disposed about a periphery of said lens engaging said packing means, said packing means being adhesively secured to said lens and said faceplate, and means for securing said faceplate to said housing means to apply a force on said packing means directed against said inclined wall whereby the packing means is forced toward said lens to provide a compressive force about the periphery thereof.

4. A sight glass assembly according to claim 3 wherein the lens is circular, the inclined wall is frustoconical and the faceplate is annular.

5. A sight glass assembly comprising housing means having an opening therethrough, a circular lens mounted in said opening, said opening having a peripheral, frustoconical wall inclined away from and in opposed relation to the periphery of said lens, packing means consisting of a resilient material interposed between the periphery of said lens and the inclined wall of the opening in said housing means, an annular faceplate disposed about the periphery of said lens engaging said packing means, said packing means having an annular flange portion interposed between said faceplate and said housing means, and means for securing said faceplate to said housing means to apply a force on said packing means directed against said inclined wall whereby the packing means is forced toward said lens to provide a compressive force about the periphery thereof.

6. A sight glass assembly according to claim 5 wherein said packing means is adhesively secured to said lens and said faceplate.

7. A sight glass assembly comprising housing means having an opening therethrough, a circular lens mounted in said opening, said opening having a peripheral frustoconical wall inclined away from and in an opposed relation to the periphery of said lens, packing means consisting of resilient materials interposed between the periphery of said lens and the inclined wall of the opening in said housing means, an annular faceplate disposed about the periphery of said lens engaging said packing means, annular cushioned gaskets interposed between the lens and the housing means and the lens and the faceplate, and means for securing said faceplate to said housing means to apply a force on said packing means directed against said inclined wall whereby the packing means is forced toward said lens to provide a compressive force about the periphery thereof.

8. A sight glass assembly according to claim 7 wherein said packing means is adhesively secured to said lens and said faceplate.

9. A sight glass assembly comprising housing means having an opening therethrough, a circular lens mounted in said opening, said opening having a peripheral, frustoconical wall inclined away from and in opposed relation to the periphery of said lens, packing means consisting of a resilient material interposed between the periphery of said lens and the inclined wall of the opening in said housing means, an annular faceplate disposed about the lower periphery of said lens engaging said packing means, said housing structure having an annular beveled surface opposed to said faceplate, said packing means including an annular flange portion interposed between said faceplate and the annular beveled portion of said housing means, annular cushioning gaskets interposed between said lens and said housing means, and said lens and said annular faceplate, and means for securing said faceplate to said housing means to apply a force on said packing means directed against said inclined wall whereby the packing means is forced toward said lens to provide a compressive force about the periphery thereof.

10. A sight glass assembly according to claim 9 wherein said packing means is adhesively secured to said lens.

11. A sight glass assembly comprising housing means having an opening therethrough, alens mounted in said opening, said opening having a peripheral wall inclined away from and in opposed relation to the periphery of said lens, packing means consisting of a resilient material disposed in said opening between the periphery of said lens and the inclined wall of the opening in said housing means, liner means consisting of a cor rosive resistant material interposed between the lens and said packing means including an outwardly projecting flange portion, a faceplate disposed about the lower periphery of said lens engaging said flange portion of said liner means, means for securing said faceplate to said housing means to apply a force through said flange portion of said liner means directed against said inclined wall of said opening whereby the packing means is forced toward the lens to provide a compressive force about the periphery of the lens and packing means disposed between the periphery of said lens and said faceplate.

12. A sight glass assembly according to claim 11, wherein the lens is circular, the inclined wall is frustoconical, the liner means is cylindrical having an annular flange portion and the faceplate is annular.

13. A sight glass assembly according to claim 12, wherein the packing means is provided with an annular flange portion interposed between the said flange portion of the liner means and said housing means.

14. A sight glass assembly according to claim 12, wherein annular cushioning gaskets are interposed between the lens and the housing means and the lens and the faceplate.

15. A sight glass assembly accordingly to claim 11, wherein the lens is circular, the opening wall is frustoconical, the liner means is cylindrical having an annular flange portion, the faceplate is annular, the housing structure is provided with an annular beveled surface opposed to the annular flange portion of the liner means, the packing means includes an annular flange portion of the liner means, the packing means includes an annular flange portion interposed between the annular portion of the liner means and the annular beveled surface of the housing means and annular cushioning gaskets are provided between the lens and the housing means and the lens and the annular faceplate.

16. A lens unit adapted to be mounted in a sight glass assembly including housing means having an opening therethrough, the opening having an inclined wall, comprising a lens mountable in said opening so that the periphery thereof will oppose said inclined wall of said opening, a packing means consisting of a resilient material adhesively secured to the periphery of said lens whereby the packing means is interposed between the periphery of the lens and the inclined wall of said opening when said lens is mounted within said opening, a faceplate disposed about the lower periphery of said lens adhesively secured to said packing means and means for securing said faceplate to said housing means when said lens is mounted in said opening to apply a force on said packing means directed against said inclined wall whereby the packing means is forced toward the lens to provide a compressive radial force about the periphery of said lens.

17. A lens unit adapted to be mounted in a sight glass assembly including housing means having an opening therethrough, the opening having an inclined wall, comprising a faceplate having an opening therein, a lens secured to said faceplate across the opening thereof, liner means consisting of a corrosive resistant material disposed about the periphery of said lens including an outwardly projecting portion engageable with said faceplate, packing means consisting of a resilient material disposed on said liner means engageable with said inclined wall of the opening in said housing means when said lens is inserted in the opening of said housing means and means for securing said faceplate of said housing means to apply a force through said flange portion of said liner means directed against said inclined wall of the opening of said housing means whereby the packing means is forced toward the lens to provide a compressive force about the periphery of the lens.

Claims

1. A sight glass assembly comprising housing means having an outer side, an inner side mountable on a vessel wall having an opening therein and an opening therethrough registrable with the opening in said wall when said housing means is mounted on said wall, a lens having outer and inner sides mounted in said opening of said housing means, said opening in said housing means having a peripheral wall inclined away from and in opPosed relation to the periphery of said lens, packing means consisting of a resilient material interposed between the periphery of said lens and the inclined wall of the opening in said housing means, a faceplate disposed about the inner periphery of said lens engaging said packing means and means for securing said faceplate to the inner side of said housing means to apply a force on said packing means directed against said inclined wall whereby the packing means is forced toward said lens to provide a compressive force about the periphery thereof.

11. A sight glass assembly comprising housing means having an opening therethrough, a lens mounted in said opening, said opening having a peripheral wall inclined away from and in opposed relation to the periphery of said lens, packing means consisting of a resilient material disposed in said opening between the periphery of said lens and the inclined wall of the opening in said housing means, liner means consisting of a corrosive resistant material interposed between the lens and said packing means including an outwardly projecting flange portion, a faceplate disposed about the lower periphery of said lens engaging said flange portion of said liner means, means for securing said faceplate to said housing means to apply a force through said flange portion of said liner means directed against said inclined wall of said opening whereby the packing means is forced toward the lens to provide a compressive force about the periphery of the lens and packing means disposed between the periphery of said lens and said faceplate.

13. A sight glass assembly according to claim 12, wherein the packing means is provided with an annular flange portion interposed between said flange portion of the liner means and said housing means.

15. A sight glass assembly accordingly to claim 11, wherein the lens is circular, the opening wall is frustoconical, the liner means is cylindrical having an annular flange portion, the faceplate is annular, the housing structure is provided with an annular beveled surface opposed to the annular flange portion of the liner means, the packing means includes an annular flange portion interposed between the annular portion of the liner means and the annular beveled surface of the housing means and annular cushioning gaskets are provided between the lens and the housing means and the lens and the annular faceplate.

17. A lens unit adapted to be mounted in a sight glass asSembly including housing means having an opening therethrough, the opening having an inclined wall, comprising a faceplate having an opening therein, a lens secured to said faceplate across the opening thereof, liner means consisting of a corrosive resistant material disposed about the periphery of said lens including an outwardly projecting portion engageable with said faceplate, packing means consisting of a resilient material disposed on said liner means engageable with said inclined wall of the opening in said housing means when said lens is inserted in the opening of said housing means and means for securing said faceplate to said housing means to apply a force through said flange portion of said liner means directed against said inclined wall of the opening of said housing means whereby the packing means is forced toward the lens to provide a compressive force about the periphery of the lens.