SCUBA DIVING AIR TANK GAUGE

TECHNICAL FIELD The present invention relates to a scuba diving air tank gauge .

More specifically, the present invention relates to a gauge for measuring the air pressure in a scuba diving air tank, the gauge being of the type comprising a casing with an inlet fitting integral with the casing and having a conduit connectable to the tank; and a Bourdon measuring device, in turn comprising a closed metal tube for receiving pressurized air from the tank. BACKGROUND ART Because a scuba diving air tank may contain air at an initial pressure of 300-400 atmospheres, the casing of known gauges of the type described above is always made of metal, in one piece with the radial inlet fitting, with obvious problems in terms of weight and cost.

An important point to note as regards manufacturing cost, in particular, is that a metal casing normally calls for a protective cover of elastic material, and extreme care must be taken when welding the inlet end of the roughly 1 mm diameter closed tube to the end of the radial inlet fitting conduit terminating inside the casing. Poor welding, in fact, may result in explosion of the gauge and, more importantly, in uncontrolled air

leakage from the tank.

An obvious solution to the weight problem is to mold the casing and the inlet fitting from lighter non- metal material, such as plastic. This, however, poses problems in fluidtight connecting the closed tube (metal) to the conduit of the inlet fitting (non-metal) , and in devising a plastic casing, as yet to be achieved, with an inlet fitting capable of withstanding the internal pressure to which the fitting is normally subjected.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a scuba diving air tank gauge which is cheap and easy to produce and, at the same time, provides for solving the above problems.

According to the present invention, there is provided a scuba diving air tank gauge as claimed in Claim 1 and preferably in any one of the Claims depending directly or indirectly on Claim 1. BRIEF DESCRIPTION OF THE DRAWINGS

A number of non- limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a plan view of a gauge in accordance with the present invention;

Figure 2 shows a section along line II-II in Figure 1 and relative to a first preferred embodiment of the gauge according to the present invention;

Figure 3 shows a larger-scale exploded view of a detail in Figure 2;

Figure 4 shows a section along line IV-IV in Figure 1 and relative to a second preferred embodiment of the gauge according to the present invention;

Figure 5 shows a section along line V-V in Figure 4;

Figure 6 shows a larger-scale exploded view of a detail in Figure 4. BEST MODE FOR CARRYING OUT THE INVENTION

With reference in particular to Figures 2, 4 and 5, number 1 indicates as a whole a gauge assembly for a scuba diving air tank (not shown) . Assembly 1 comprises a gauge 2; and a hose 3 connectable at one end to the tank (not shown) , and having, at the other end, an outlet fitting 4 for connecting gauge 2 removably and in rotary and fluidtight manner to hose 3.

Gauge 2 comprises a cup-shaped plastic casing 5 closed by a transparent cover 6 and housing a dial 7 facing transparent cover 6. Casing 5 also houses a Bourdon measuring device 8 comprising a closed metal tube 9 wound into a coil 10, which is positioned parallel to dial 7 and has, at the end connected to the tank (not shown) , a straight inlet end portion 11 extending substantially radially with respect to coil 10. Measuring device 8 also comprises a pointer 12 fitted to a shaft 13, which is fitted to casing 5 to rotate about a longitudinal axis 14 of casing 5, and

defines the output of measuring device 8. Shaft 13 is connected to a closed end of spiral 10, opposite the end connected to straight inlet end portion 11; and pointer 12 is visible from the outside through transparent cover 6, and is moved by spiral 10 along a scale 15 of pressure values marked on dial 7, to indicate, on scale 15, the residual pressure in the tank.

Casing 5 comprises a bottom wall 16 crosswise to axis 14; and a substantially cylindrical outer lateral wall 17, on the free end of which is formed an annular face groove 18.

Transparent cover 6 is made of thermoplastic material, is cup-shaped with its concavity facing the concavity of casing 5, and comprises a substantially circular front wall 19; and a lateral wall 20 bounded, on the side facing casing 5, by two flat annular surfaces 21 and 22. Annular surface 21 is positioned facing a similar flat annular end surface 23 of casing 5, and cooperates with annular surface 23 to lock the periphery of dial 7 in position; and annular surface 22 secures a seal 24 inside annular groove 18.

Casing 5 comprises an inlet fitting 25, which is made of plastic, is integral with casing 5, and extends radially outwards from lateral wall 17. Inlet fitting 25 comprises an axial inner conduit 26, which communicates at one end with the inside of casing 5, and at the other end with hose 3 via outlet fitting 4 of hose 3; and an external thread 27, which is

engaged by outlet fitting 4 of hose 3 to connect gauge 2 removably and in fluidtight and rotary manner to hose 3. For which purpose, outlet fitting 4 comprises a socket 28, the inner chamber of which communicates, though its end wall, with a tubular appendix 29 fitted inside hose 3, and receives in fluidtight manner a cylindrical spigot 30 described in more detail below, and the outer surface of which has an annular groove engaged by an 0-ring 31. The outer surface of socket 28 has an annular groove engaged in rotary manner by an inner flange 32 of a sleeve 33, which is partly engaged in rotary manner by socket 28, and has a fully threaded portion projecting beyond an end edge 34 of socket 28 and engaging external thread 27 of inlet fitting 25. In the Figure 2 and 3 embodiment, inlet fitting 25 has a small-diameter end appendix 35 bounded at its free end by an annular edge 36, and having thread 27 on its outer surface. And conduit 26 has a constant-section cylindrical portion 37 communicating with the inside of casing 5; and a constant-section cylindrical portion 38, which is coaxial with portion 37, is larger in inside diameter than portion 37, extends partly along appendix 35, and communicates at one end with portion 37, and at the other end with the outside of gauge 2. As shown more clearly in Figure 3, the straight inlet end portion 11 of closed tube 9 engages portion 37 of conduit 26 with a relatively small radial clearance of about 0.25 mm, comes out at one end inside portion

38, and is fixed in fluidtight manner inside portion 37 with the interposition of a tubular layer 39 of adhesive material, preferably acrylic glue. Portion 38 is substantially identical in section to socket 28, and is sized crosswise to receive a spigot 40 of a two-spigot tubular sealing member 41 normally made of metal, and the other spigot of which, opposite and coaxial with spigot 40, is defined by spigot 30 and separated from spigot 40 by a central outer flange 42. Like spigot 30, spigot 40 has an annular groove on its outer surface engaged by an 0-ring 43, and, as shown in Figure 2, is inserted in fluidtight manner, in use, inside portion 38, so that flange 42 contacts annular edge 36 of appendix 35; and spigot 30 is inserted in fluidtight manner, in use, inside socket 28, the end edge 34 of which presses flange 42 against annular edge 36 when sleeve 33 is screwed onto thread 27.

In the Figure 4-6 embodiment, inlet fitting 25 has a further small-section tubular appendix, which projects from annular edge 36 of appendix 35, coaxially with appendix 35, and defines spigot 30. In other words, in the Figure 4-6 embodiment, tubular sealing member 41 is eliminated, and spigot 30, in this case made of plastic, is integral with the rest of gauge 2 and, in use, engages socket 28; and, when sleeve 33 is screwed onto thread 27, the end edge 34 of socket 28 contacts an annular shoulder defined by the part of annular edge 36 left exposed by the small-section tubular appendix

defining spigot 30.

In the Figure 4-6 embodiment, conduit 26 has a constant section, the size of which is similar to that of portion 37 along substantially the whole of its length, and forms, at its inlet end, a wider-section socket 44 communicating with the outside and formed on the free end of the appendix defining spigot 30.

As shown more clearly in Figure 6, the straight inlet end portion 11 of closed tube 9 engages the whole of conduit 26, extends through socket 44, projects from socket 44 at the end, and is fixed in fluidtight manner inside conduit 26 with the interposition of a tubular layer 45 of adhesive material, preferably acrylic glue, which at least partly fills the inside of socket 44 and the rest of conduit 26 not occupied by straight inlet end portion 11 of closed tube 9.

By means of the above design solutions, gauge 2 can be made of molded plastic material, and closed tube 9 connected cheaply and easily in fluidtight manner to inlet fitting 25. In this connection, it should be pointed out that inserting straight inlet end portion 11 inside conduit 26, and gluing straight inlet end portion 11 in fluidtight manner to the inner surface of conduit 26 substantially prevent inlet fitting 25 from being subjected to severe internal pressure in use.

This of course only applies if straight inlet end portion 11 of coil 10 is glued properly inside conduit 26 and in such a manner as to prevent pressurized-air

flow into the gap between the outer surface of straight inlet end portion 11 and the inner surface of conduit 26, which would result not only in severe internal stress of radial inlet fitting 25, but also in pressurized-air flow into casing 5 and explosion of transparent cover 6.

In the Figure 2 and 3 embodiment, the risk of this happening is substantially non-existent, by virtue of the relatively short length of conduit 26 assisting complete penetration of the glue and perfect gluing of straight inlet end portion 11 to radial inlet fitting 25.

The same cannot safely be said for the Figure 4 to 6 embodiment, however, on account of the much longer length of conduit 26.

In this case therefore, as shown in Figure 4, to ensure the glue is pumped properly into conduit 26 and the formation of a continuous tubular layer 45 of adhesive between straight inlet end portion 11 and radial inlet fitting 25, an intermediate portion of conduit 26 is connected to the outside by a radial hole 46 of roughly the same diameter as conduit 26, and through which to pump ^" pressurized glue into conduit 26.

In a variation not shown, the Figure 2 and 3 embodiment is also provided with hole 46.

As shown more clearly in Figures 4 and 6, the Figure 4-6 embodiment preferably comprises a safety device 47 defined by at least one radial hole 48 (and

preferably two, as in the example shown, or more) formed through radial inlet fitting 25, between radial hole 46 and spigot 30.

Radial hole 48 is a capillary hole, which, unlike what is shown for reasons of clarity, is much smaller in section than the gap between straight inlet end portion 11 and conduit 26, connects conduit 26 to the outside, is not filled with glue, given its small cross section, but provides for exhausting any pressurized air penetrating between the inner surface of conduit 26 and the outer surface of straight inlet end portion 11.

Safety device 47 not only safeguards against pressurized air reaching casing 5 outside measuring device 8, but also serves to indicate any gluing defects.