US3677020A

US3677020A - Method and apparatus for forming carbon dioxide snow

Info

Publication number: US3677020A
Application number: US41150A
Authority: US
Inventors: Edward A Munselle
Original assignee: EDWARD A MUNSELLE
Current assignee: EDWARD A MUNSELLE
Priority date: 1970-05-25
Filing date: 1970-05-25
Publication date: 1972-07-18
Anticipated expiration: 1989-07-18

Abstract

A fitting is attached to the conventional valve of the standard carbon dioxide siphon cylinder. The fitting has an expansion orifice that is positioned immediately adjacent the outlet port of the valve. The position of the orifice and its size, within the range of 0.005 through 0.012 inches, maximize efficiency of production of solid carbon dioxide and minimize time lag between starting and stopping of production upon operation of the standard valve. The expansion orifice is provided by a readily removable and replaceable insert of the fitting and provision is made for quickly securing to the fitting a number of attachments including a curved conduit that optimizes production of solid carbon dioxide in flake form.

Description

United States Patent Munselle [54] METHOD AND APPARATUS FOR FORMING CARBON DIOXIDE SNOW [72] lnventor: Edward A. Munselle, 12591 Singing Woods Road, Santa Ana, Calif. 92706 [22] Filed: May 25,1970

[21] App1.No.: 41,150

Daniels ..137/67 1 July 18, 1972 2,681,707 6/1954 Mapes ..169/1l 2,925,224 2/1960 Cunningham ..239/600 Primary Examiner-Norman Yudkoff Assistant ExaminerS. Silverberg Attorney-Causewitz & Carr ABSTRACT A fitting is attached to the conventional valve of the standard carbon dioxide siphon cylinder. The fitting has an expansion orifice that is positioned immediately adjacent the outlet port of the valve. The position of the orifice and its size, within the range of 0.005 through 0.012 inches, maximize efi'iciency of production of solid carbon dioxide and minimize time lag between starting and stopping of production upon operation of the standard valve. The expansion orifice is provided by a readily removable and replaceable insert of the fitting and provision is made for quickly securing to the fitting a number of attachments including a curved conduit that optimizes production of solid carbon dioxide in flake form.

14 Claims, 5 Drawing Figures PATENTEDJULIBmz 3.671.02

4 \NVENTOR fii EWAED A. MUNEELLE AT TOP-N ETS METHOD AND APPARATUS FOR FORMING CARBON DIOXIDE SNOW BACKGROUND OF THE INVENTION Field of the Invention The present invention concerns the formation of solidified carbon dioxide, and more particularly relates to methods and apparatus for converting pressurized liquid carbon dioxide into carbon dioxide snow.

Description of Prior art Solid carbon dioxide or carbon dioxide snow, having a temperature of approximately l09 F. at atmospheric pressure, sublimes, that is, changes directly from solid to gaseous state at room temperature and below. These properties are among those that make this material widely useful for a number of purposes, including dermatology, surgery, various scientific and laboratory purposes, portable refrigeration, and others. Commercially produced solid carbon dioxide in the form of dry ice is available only in relatively large quantities, is difficult to transport and handle and requires special facilities for storage because of its low temperature. It is not readily applicable for many purposes that require use of small quantities at specific locations. Accordingly, for dermatological use and other special purposes, there is widely available a standard pressurized cylinder of liquid carbon dioxide normally being about two-thirds full of liquid with the other third filled with carbon dioxide gas.

At room temperature, such gas is at a pressure of approximately 852 psi. A standard carbon dioxide disc valve is fitted on the cylinder and has the inlet port thereof connected by means of a siphon tube to the bottom portion of the cylinder. Solid carbon dioxide may be formed from such a standard cylinder and valve arrangement by carefully opening the valve a precise amount to thereby expand the pressurized, confined liquid carbon dioxide through a very small valve opening. A cloth or bag or the like is placed immediately adjacent and substantially surrounding the valve outlet to cause the escaping and expanding gas to solidify on the bag or cloth.

This arrangement is commonly practiced at present to collect and form solid carbon dioxide for dermatological and surgical purposes. However, it is exceedingly difficult with the standard carbon dioxide valve to obtain the proper amount of valve opening because such a small opening is required for formation of solids. If, as so often happens, the valve opening is too great, velocity of discharged gas is excessive and much of the escaping gas fails to solidify. Nevertheless, large amounts of solid may be rapidly formed in this manner with still greater losses of carbon dioxide that remain in gaseous form and dissipate in the ambient atmosphere. Formation of small quantities of solid is quite difficult to control.

The inconvenience, inefficiency and difficulties in controlling the amount of carbon dioxide snow made with such devices has long been recognized as indicated by the U.S. Pat. No. 1,965,922 to H. Fievet, and U.S. Pat. No. 947,382 to J. C. Goosmann, for example. These suggest special collecting cylinders or molds to receive carbon dioxide discharged from a pressurized cylinder and provide amounts of the solid that are readily compressed or formed into desired portable bodies or cakes. These arrangements, although providing solid carbon dioxide in a conveniently applicable size and shape, still experience the previously mentioned difficulty arising through the inconvenience and inefficiency of controlling the formation of solids through the use of the standard carbon dioxide cylinder valve.

In attempting to improve convenience of the formation and application of dry ice or carbon dioxide snow, particularly for surgical purposes, Batzle in U.S. Pat. No. 2,307,013, and Fregang in U.S. Pat. No. 2,493,759, employ relatively complex receptacles, closures, and molds specifically arranged for use with standard self-contained sealed containers or cartridges of liquid carbon dioxide. These containers, which are substantially conventional arrangements employed for charging soda siphons at home, replace the usual valving arrangements with metal seals that are punctured when use of the cartridge contents is required. The apparatus suggested by Batzle and Fregang are limited to formation of solid carbon dioxide in specific shapes and quantities as dictated by the size and shape of the specific receptacle or mold thereof. Furthermore, these must either use the entire contents of the cartridge at one time or rely for storage protection on the sealing arrangement specially built into the apparatus itself. The devices of Batzel and Fregang do not show or suggest critical orifice dimensions for optimum efficiency of conversion of liquid into solid form and, furthermore, cannot readily control the density of the solid that is produced.

Accordingly, it is an object of this invention to provide an apparatus and method for converting liquid carbon dioxide into solid form most efficiently and in a variety of densities while avoiding disadvantages of previous arrangements.

SUMMARY OF THE INVENTION In carrying out the principles of this invention in accordance with a preferred embodiment thereof, the standard valve of a liquid carbon dioxide vessel is operated. Released carbon dioxide is confined within a relatively small volume that is substantially wholly within the standard valve on the downstream side of the valve closure member. The carbon dioxide so confined is then expanded through an orifice immediately adjacent the valve. Preferably, the orifice has a diameter in the range of 0.005 through 0.012 inches. In order to form the solid carbon dioxide in a low density snowflake form, the carbon dioxide discharged through the orifice is confined to a short, curved path, to thereby eliminate the previously required porous bag or screen immediately adjacent the orifice. With this arrangement solid carbon dioxide in flake form is continuously discharged as a snow into an unconfined volume of ambient atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a carbon dioxide siphon cylinder having a standard carbon dioxide valve and the fitting of the present invention attached thereto,

FIG. 2 is an enlarged sectional view of a fitting of the present invention,

FIG. 3 is an enlarged view of the orifice bearing insert of the fitting of FIG. 2,

FIG. 4 illustrates a curved attachment for the fitting of FIG. 2, particularly arranged for the production of solid carbon dioxide in flake form, and

FIG. 5 illustrates a flexible tube adapted to be attached to the fitting of FIG. 2 and employed for refrigeration of a glass.

DESCRIPTION OF THE PREFERRED EMBODIMENT As illustrated in FIG. 1, a standard carbon dioxide siphon cylinder includes a steel vessel 10 having a neck 12 in which is mounted and sealed a standard carbon dioxide valve 14. The vessel 10 is normally about two-thirds filled wit liquid carbon dioxide and one-third filled with gaseous carbon dioxide at a pressure determined by ambient temperature, normally about 852.4 psi at 70 F. The standard valve schematically depicted in FIG. I, conventionally includes an inlet port 16 in fluid communication with the interior of the vessel 10 by means of a siphon tube 18. The valve also has an outlet port 20 and a valve closure member 22 that is operable between closed and open position by a valve handle 24. The valve body includes an interior valve chamber between the inlet and outlet ports. This chamber is normally filled with carbon dioxide when the valve is open and carbon dioxide is being discharged from the cylinder. The valve outlet port 20 normally has a substantially flat sealing face 28 (which may be annularly grooved to receive a sealing O-ring) that is usually sealed against a sealing face of a cooperating fitting for attachment of a pressure regulator or other apparatus to the carbon dioxide cylinder.

In accordance with the illustrated embodiment of the present invention, a fitting 32 is removably secured to the externally threaded outlet port 20 by means of a conventional coupling nut 34. Fitting 32 has a sealing face 36 thereof maintained in sealing engagement with face 28 of the port 20. As more specifically illustrated in FIG. 2, fitting 32 includes a body portion 38 having an internal bore 40, with the sealing face 36 formed at the inner end of the fitting. The sealing face of the fitting is formed by an annular protrusion 42 having an outwardly facing concave surface that cooperates with the inwardly directed concave surface of an annular washer 44 to confine a sealing O-ring 43 therebetween. The O-ring protrudes slightly from the sealing face of the fitting whereby the coupling nut 34 compresses the O-ring against and between the sealing faces of the fitting and outlet port of the valve.

A recess 46 is formed centrally of the fitting 32 and includes a shoulder 48 for reception of an insert 50 that is shown in detail in FIG. 3. Insert 50 includes a body portion 52 that is received within the internal bore 40 of the fitting. The insert is hollow and includes an enlarged head portion 54, integral with body 52. The head portion 54 is adapted to be sealed against the shoulder 48 of the bore 40 of the fitting 38 by means of an O-ring 56 that is positioned between the head portion 54 and the shoulder.

Head portion 54 has an external surface 58 in which is formed a gas expanding orifice 60. For optimum operation, maximized efficiency and increased yield, the orifice has a diameter not less than 0.005 inches and no more than 0.012 inches. Within this range, it is found that a diameter of 0.008 inches provides maximum yield, ideal production time, and preferred velocity. As the orifice decreases in size from 0.008 inches, the yield of solidified carbon dioxide decreases, the time required to produce a given amount of solid product increases, and velocity of the projected solid particles decreases. As the orifice is increased in size from 0.008 to 0.012 inches, the yield of solidified product is decreased, production time is decreased, and velocity of gas and solidified product as discharged is increased. It is found that with an orifice less than 0.005 inches, the apparatus will readily be plugged with dirt or frozen moisture included within the vessel. At diameters above 0.012, it is found that greatly increased velocity of discharged material occurs and increased proportions of discharged carbon dioxide remain in gaseous form without solidifying. Accordingly, efficiency is greatly decreased and collection and handling of the higher velocity solid particles becomes more difficult. For example, with orifices as large as one-sixteenth of an inch in diameter as previously suggested by others, the velocity of discharged material is exceedingly high and large amounts of material remain in gaseous form even where it is caused to impinge upon a porous collecting bag or the like.

Although but a single aperture or orifice 60 in the .exterior face 58 of the insert 50 is illustrated, the invention contemplates provision of two or more orifices, each identical to orifice 60 and each being of the previously described optimum size of about 0.008 inches. Each of such apertures is formed in the external face 58 and all are directly in communication with the interior of the outlet port 20 at the sealing surface 28 thereof. Such additional orifices permit increased production of solidified carbon dioxide or, stated in another fashion, permit decreased production time of a given amount of carbon dioxide, all without departing from the optimum efficiency of solidification and without varying the optimum velocity that is produced by the orifice of specified size.

Fitting 32 has the outer end portion thereof arranged to receive and hold in sealing engagement a variety of readily replaceable attachments of which one is illustrated at 62 in FIG. 1. Attachment 62 comprises a short length of tubing that is flared at its outer end portion as illustrated in order to direct the discharged stream as desired. Attachment 62, and other attachments and all of the fitting and parts thereof, except the O-rings, are preferably formed of a hard metal such as brass,

bronze or other copper alloys well known in the art.

The rigid metallic attachments are held on the outer end of the fitting 32 by means of a resilient O-ring 64 that is retained within a circumferential groove 66 formed on the exterior surface of the outer end of the fitting. A shoulder 68 provides a stop against which the inner end of the rigid attachment will abut for proper positioning.

In addition to rigid metallic attachments such as that illustrated at 62, flexible tubing may be replaceably secured on and sealed to the outer end of fitting 32. Such tubing is retained in place by a plurality of longitudinally spaced circumferential

barbed surfaces

70, 72, adapted to receive and resiliently deform the interior of the smooth bore of such flexible tubing.

It will be readily appreciated that with the illustrated arrangement of the outer end of fitting 32, a variety of different sizes, shapes and designs of attachments may be employed as particularly appropriate for specific purposes. It is found that a curved attachment such as that illustrated in FIG. 4, enables production of carbon dioxide in solid form of minimum density and by direct discharge into ambient atmosphere, as more particularly described below.

As well known, production of solid carbon dioxide by means of rapid expansion of the material in liquid form is achieved by discharge of the liquid through an expansion orifice and causing it to almost immediately impinge upon a surface that enables formation of the solid and dispersion of the unsolidified gaseous portion. Thus, with the attachment 62 illustrated in FIG. 1, solidified carbon dioxide is produced by placing a porous bag or a porous paper such as paper towelling closely adjacent the outer end of attachment 62 or in some in stances, surrounding the attachment 62, and then opening the valve 14 to any desired amount. The action that takes place, involves first release of pressurized liquid into the relatively small volume chamber within the body of the valve, between its inlet and outlet ports, wherein it is substantially confined. The exterior surface 58 of insert 50 forms, in effect, a partial closure for this volume even when valve disc 22 is moved away from its seat to open the valve. Pressurized liquid carbon diox ide confined within the valve body is discharged through the orifice 60 whereupon it expands and travels through the bore of fitting 32, through attachment 62, to impinge upon a collecting surface that is preferably located within about an inch of the outer end of the attachment 62. Before expansion through orifice 60 can take place, of course, the chamber within the valve on the downstream side of valve closure member 22 must be filled with the liquid carbon dioxide.

The described arrangement minimizes the volume of this chamber that must be filled upon startup of the solid carbon dioxide production, and thus also decreases the time lag between opening of the valve 24 and production of solid. In prior arrangements, wherein the orifice is located as much as a foot or more from the valve itself, being positioned within the end of a hose, for example, the entire interior of such hose in addition to the chamber within the valve body itself must first be filled with the liquid before solid production can be started. When production of solid carbon dioxide is to be terminated, the main valve 14 is closed to prevent further discharge of liquid through the valve. Nevertheless, the valve chamber and whatever hose there may be, as in prior art devices, on the downstream side of the valve closure member 22 remains filled with the liquid which thus continues to be discharged through the orifice until all is dissipated.

Thus it will be seen that the illustrated fitting that provides positioning of the orifice 60 as close as practically possible to the standard carbon dioxide shutoff valve minimizes the start and stop time and minimizes waste of material. With the illustrated arrangement, a maximum amount of carbon dioxide snow may be made in a minimum amount of time with a minimum consumption and waste of fluid. The amount of residual loss due to piping and the like is substantially negligible.

Although, as described above, maximum efficiency and timing is provided by the illustrated arrangement with the attachment 62 of FIG. 1, this arrangement and attachment still require use of a porous surface closely adjacent to the attachment for optimum operation. Furthermore, this arrangement produces solid carbon dioxide of relatively high density. It is found that when the material discharged through the orifice 60 is confined to a curved path through a short distance of its initial travel, the gas solidifies directly in a low density flake form as it passes into the ambient atmosphere. This occurs without any impingement of the gas upon another surface.

Thus, when attachment 62 is replaced with an attachment such as illustrated in FIG. 4 at 74, the gas discharged from orifice 60 enters the inner end 76 of the attachment through the outer end of fitting 32, is confined to a short, right angle path by the 90 bend of the attachment, and exits through the enlarged outer end 78 of attachment 74. With such curved path of the discharged gas, it is found that at a distance of several inches from the outer end of the attachment, the gas begins to solidify, as indicated at 79 in a form of exceedingly low density which, when formed in ambient air, will float lightly downwardly. The solid material thus formed slowly descends and is quite similar in appearance to ordinary snowflakes.

The low density material thus formed has many applications in addition to those commonly available with solid carbon dioxide. The flake form of lower density is much easier to mix in a slurry which can be brushed onto tissue for dermatological purposes. Furthermore, the formation of the low density snowflakes which occur directly in air can be readily employed for portable refrigeration purposes. Thus, for example, a given article may easily be covered with a blanket of carbon dioxide snow by directing the outer end 78 of the curved nozzle 74, and positioning this immediately above an area to be covered with the snow. The nozzle is moved over the area that is to be blanketed, maintaining the no71le at a distance of a foot or two above the area to be covered.

For application as a portable refrigeration apparatus, the arrangement illustrated has many uses. For example, as shown in FIG. 5, a common drinking glass 80 may be chilled by attachin g a flexible resilient tube 82 to the outer end of fitting 32 in the place of attachment 62. The flexible tube 82 is secured to and retained by the

barbed surfaces

70, 72 of the fitting. In this arrangement, curvature of the tube 82, acts in much the same manner as the curvature of attachment 74 to confine the discharged gas to a curved path whereby flakes of solid carbon dioxide are formed without the requirement of impingement upon a surface adjacent to the gas particles or gaseous steam. Thus, the attachment shown as a flexible tube 82 in FIG. 5 may produce the same snow blanket directly in air as is produced by the curved attachment 74 of FIG. 2. This has the additional advantage of allowing traverse of the point of formation carbon dioxide flakes over a relatively larger area without moving the entire pressure cylinder and valve.

In summary, it will be readily appreciated that the described method and apparatus has wide application to dermatology, and certain surgical procedures. It may be used for educational and scientific purposes involving change of states of materials, Various types of portable refrigeration effects are readily available including pre-chilling of vessels, such as drinking glasses and covering of small objects. For example, a group of canned liquids may be covered with a readily applicable blanket of carbon dioxide snow for quick and efficient refrigeration. Further, in certain types of welding where inert atmosphere is required, the method and apparatus described herein may be arranged for production of carbon dioxide gas with maximum efficiency from a liquid carbon dioxide containing vessel. in any of these applications, the apparatus and method described here provides optimal amounts of solid dry ice in a minimum period of time with minimum loss of liquid carbon dioxide and enables rapid production of small or larger quantities.

The foregoing detailed description is to be clearly understood as given by way of illustration and example only, the spirit and scope of this invention being limited solely by the appended claims.

I claim:

1. Apparatus for forming a spray of carbon dioxide snow comprising a vessel containing liquid carbon dioxide,

a standard valve mounted on the vessel and having a valve 5 body,

an inlet port in said body in communication with the interior of the vessel,

an outlet port in said body having aport sealing face,

a valve closure member movably mounted in said body to block or allow fluid flow through said body from said inlet to said outlet port, and

an expansion fitting secured to said valve, said fitting comprising a sealing face in fluid tight engagement with the sealing face of said outlet port,

a recess centrally positioned in said fitting sealing face and in fluid communication with the interior of said fitting,

an insert mounted within said recess and having an external face substantially coplanar with said fitting sealing face, and

an orifice in said coplanar external face of said insert, whereby escaping fluid will commence expansion through said orifice at the sealing face of said outlet port.

2. The apparatus of claim 1 wherein said orifice has a diameter in the range of 0.005 inches through 0.012 inches.

3. The apparatus of claim 2 wherein said orifice has a diameter of about 0.008 inches.

4. The apparatus of claim 2 including a curved conduit in fluid communication with the interior of said fitting to direct and confine discharged carbon dioxide in a curved path.

5. The apparatus of claim 2 wherein said fitting includes an external circumferential groove, and an O-ring in the groove, whereby a conduit with a smooth internal bore may be detachably secured to the fitting and sealed thereto by said O-ring.

6. The apparatus of claim 5 wherein said fitting includes a plurality of longitudinally spaced circumferential barbed surfaces adapted to receive and seal the internal surface of a resilient tube.

7. The apparatus of claim 2 wherein said recess has an internal shoulder, said insert comprising a hollow body extending into the interior of said fitting and having an enlarged head seated upon said recess shoulder, said external face comprising the exterior of said insert head.

8. The apparatus set forth in claim 2 including a conduit having a smooth internal bore snugly engaging the outer end of said fitting and sealed thereto, said conduit being substantially curved and terminating in an enlarged nonle.

9. For use with a pressurized container of liquid carbon dioxide having a valve with an outlet port and a port sealing face, a liquid expanding fitting comprising a sealing face in fluid tight engagement with the sealing face of said outlet port,

a member having an orifice considerably smaller than said outlet port, said orifice member comprising an insert mounted within said recess and having an external face substantially coplanar with said fitting sealing face, and

an orifice in said coplanar external face of said insert, and

means for holding said orifice member in sealing relation to said port with the orifice of said member substantially in the plane of said port sealing face.

10. The fitting of claim wherein said orifice has a diameter in the range of 0.005 through 0.012 inches.

11. The fitting of claim wherein said orifice has a diameter of about 0.008 inches.

12. The apparatus of claim 9 wherein said orifice has a 75 diameter in the range of 0.005 inches through 0.012 inches.

13. The apparatus of claim 12 including a curved conduit in fluid communication with the interior of said fitting to direct and confine discharged carbon dioxide in a curvedpath.

14. Apparatus for forming a spray of carbon dioxide snow comprising a vessel containing liquid carbon dioxide, a standard valve mounted on the vessel and having a valve body,

an inlet port in said body in communication with the interior of the vessel,

an outlet port in said body having a port sealing face,

a recess centrally positioned in said fitting face and in fluid communication with the interior of said fitting,

an orifice in said external face of said insert, said fitting sealing face including an annular protrusion having a concave outer surface,

an O-ring circumscribing said protrusion, and

an annular washer circumscribing said protrusion and having a concave inner surface,

said O-ring being retained by and between said concave surfaces.

Claims

2. The apparatus of claim 1 wherein said orifice has a diameter in the range of 0.005 inches through 0.012 inches.
3. The apparatus of claim 2 wherein said orifice has a diameter of about 0.008 inches.
4. The apparatus of claim 2 including a curved conduit in fluid communication with the interior of said fitting to direct and confine discharged carbon dioxide in a curved path.
5. The apparatus of claim 2 wherein said fitting includes an external circumferential groove, and an O-ring in the groove, whereby a conduit with a smooth internal bore may be detachably secured to the fitting and sealed thereto by said O-ring.
6. The apparatus of claim 5 wherein said fitting includes a plurality of longitudinally spaced circumferential barbed surfaces adapted to receive and seal the internal surface of a resilient tube.
7. The apparatus of claim 2 wherein said recess has an internal shoulder, said insert comprising a hollow body extending into the interior of said fitting and having an enlarged head seated upon said recess shoulder, said external face comprising the exterior of said insert head.
8. The apparatus set forth in claim 2 including a conduit having a smooth internal bore snugly engaging the outer end of said fitting and sealed thereto, said conduit being substantially curved and terminating in an enlarged nozzle.
9. For use with a pressurized container of liquid carbon dioxide having a valve with an outlet port and a port sealing face, a liquid expanding fitting comprising a sealing face in fluid tight engagement with the sealing face of said outlet port, a recess centrally positioned in said fitting sealing face and in fluid communication with the interior of said fitting, a member having an orifice considerably smaller than said outlet port, said orifice member comprising an insert mounted within said recess and having an external face substantially coplanar with said fitting sealing face, and an orifice in said coplanar external face of said insert, and means for holding said orifice member in sealing relation to said port with the orifice of said member substantially in the plane of said port sealing face.
10. The fitting of claim wherein said orifice has a diameter in the range of 0.005 through 0.012 inches.
11. The fitting of claim 10 wherein said orifice has a diameter of about 0.008 inches.
12. The apparatus of claim 9 wherein said orifice has a diameter in the range of 0.005 inches through 0.012 inches.
13. The apparatus of claim 12 including a curved conduit in fluid communication with the interior of said fitting to direct and confine discharged carbon dioxide in a curved path.
14. Apparatus for forming a spray of carbon dioxide snow comprising a vessel containing liquid carbon dioxide, a standard valve mounted on the vessel and having a valve body, an inlet port in said body in communication with the interior of the vessel, an outlet port in said body having a port sealing face, a valve closure member movably mounted in said body to block or allow fluid flow through said body from said inlet to said outlet port, and an expansion fitting secured to said valve, said fitting comprising a sealing face in fluid tight engagement with the sealing face of said outlet port, a recess centrally positioned in said fitting face and in fluid communication with the interior of said fitting, an insert mounted within said recess and having an external face substantially coplanar with said fitting sealing face, and an orifice in said external face of said insert, said fitting sealing face including an annular protrusion having a concave outer surface, an O-ring circumscribing said protrusion, and an annular washer circumscribing said protrusion and having a concave inner surface, said O-ring being retained by and between said concave surfaces.