Patent Application
20050199403
1. Field of the Invention
The present invention relates to the field of compressed air and gas systems, and more particularly to air/gas-driven tools, such as paint guns and other equipment. The present invention further relates to dryness indicators designed to visually indicate the moisture content of compressed gas or air delivered to a point of use.
2. Description of Prior Art
Typical compressed air or gas produced by a compressor apparatus is saturated with 50% to 100% relative humidity. Removal of this moisture vapor requires that an air/gas drying system be used, such as a refrigerated dryer or an adsorbent type of dryer. Such apparatus are generally very effective, the latter being typically capable of drying compressed air or gas to below-zero dew point levels. Notwithstanding such drying measures, there is unfortunately no guarantee that the compressed air or gas will have the desired dryness by the time it arrives through an air/gas feed system to a downstream point of use. Compressed air lines, various fitting and regulation devices, or improper operation of the dryer system all represent sources of residual moisture vapor entrainment in the air/gas feed system. This means that moisture-treated compressed air or gas may be carrying unwanted moisture vapor when it goes into use as an application.
One area where this problem tends to occur is in paint booth operations where compressed air or gas is used as a propellant to atomize and expel paint from a paint gun. Even though extraordinary measures are often implemented to eliminate moisture vapor at the compressed air/gas source, moisture can still be delivered to the paint gun. In some cases, this may be due to the drying system losing effectiveness due to a malfunction or other problem. However, even if the drying system is operating at full operational efficiency, the lengthy hoses connecting the air source to the paint gun can introduce unwanted moisture vapor into the system. In particular, these hoses can be disconnected and re-connected any number of times throughout the course of a painting application. Each time a disconnection occurs, moisture-laden ambient air is allowed to enter the air/gas line, and will feed through the paint gun until such time as it evacuated from the line and replaced by dry air/gas coming from the air/gas source. Any time there is excess moisture vapor in a paint gun, unwanted fouling can occur that results in a bad and unacceptable paint job. In most cases, the unsuspecting painter will assume the air/gas quality is satisfactory, particularly when there is sophisticated drying equipment operating at the air/gas source.
Various dryness indicators have been proposed for use in compressed air, gas and refrigerant applications. These typically involve the use of a moisture-adsorbing silica gel desiccant that is impregnated with a chemical moisture indicator, such as a cobalt salt. This particular chemical indicator is normally a deep blue color when it is dry, but gradually turns a light pink color in proportion to the amount of moisture that is present as the salt hydrates. In a dryness indicator, the color-indicating desiccant is placed in contact with a compressed air/gas stream within a transparent or translucent container, so that the desiccant can be viewed during operations.
Prior art dryness indicators tend to have design features that prevent them from being optimally suited for point-of-use operation in conjunction with a hand-held air/gas-driven tool, such as a paint gun, where moisture monitoring is most needed. In all of the reference materials reviewed, the prior art dryness indicators form part of a filter/dryer that requires a relatively large quantity of desiccant to effectively remove moisture for a reasonable length of time. This quantity of desiccant is more than that which is required to indicate dryness. The filter/dryers in which prior art dryness indicators are incorporated also tend to include additional elements to condense and remove moisture droplets from the air/gas stream, and to trap oil, line debris and other contaminants. As a result of the foregoing design features, most prior art dryness indicators are large or bulky, and not suitable for point-of-use operation.
It is to solving the foregoing problems that the present invention is directed. What is particularly needed is an improved compressed air/gas dryness indicator that is optimized for point-of-use operation with an air/gas-driven tool, such as a paint gun. Ideally, the dryness indicator needs to provide a visual indication identifying the exact state of dryness of the compressed air/gas line, yet must be unobtrusive and afford full freedom of movement at the point-of-use without any impediment of bulky filters, desiccant containers, cumbersome vessels, etc. The dryness indicator additionally needs to be easy to install and use, should be simple and inexpensive, and should require little or no maintenance.
The foregoing problems are solved and an advance in the art is achieved by a novel air/gas-driven tool having an air/gas dryness indicator integrated therewith. In exemplary embodiments of the invention, the dryness indicator is implemented by way of a dryness-indicating material, such as a color-changing desiccant or moisture sensitive paper, that is disposed in a cavity formed as part of the tool's air/gas flow passage. One or more view ports are provided at convenient locations for viewing the dryness-indicating material. The dryness-indicating material can be conveniently carried in an indicator cartridge that is in fluid communication with the cavity. The indicator cartridge represents a replaceable active element that can be renewed from time-to-time during the operational life of the tool. The indicator cartridge may include a vessel that defines a containment chamber for containing the dryness-indicating material.
In one embodiment in which the indicator cartridge is completely received within the air/gas-driven tool, the vessel is configured with a first and second ends and a central portion disposed between said first and second ends. The central portion of the vessel defines a containment chamber for containing the dryness-indicating material. This portion of the vessel is light transmissive so that the dryness-indicating material can be viewed externally of the vessel, through one or more view ports formed on the tool. A pair of air/gas-permeable closures cap the ends of the vessel in order to retain the dryness-indicating material therein. The closures also respectively perform pre-filtering and after-filtering functions. Each closure includes a non-planar central portion that creates a protuberance on a first side thereof extending into the containment chamber, and a plenum-defining cavity on a second side thereof facing away from the containment chamber. A seating spacer is placed in the cavity on the inlet side of the indicator cartridge in order to retain the cartridge in an installation position and provide an additional plenum. The cavity is closed by a retainer fitting that can be removed to facilitate insertion and removal of the indicator cartridge.
In another embodiment in which the indicator cartridge is mounted on a surface portion of the air/gas-driven tool and includes its own view port, the vessel containing a dryness-indicating material is configured with an air/gas permeable first end in fluid communication with the tool's air/gas flow passage and a non-permeable second end that is light transmissive so that the dryness-indicating material can be viewed externally of the vessel, with second end of the vessel providing the view port.
The invention is further directed to a replacement indicator cartridge that can be inserted within or mounted on a surface of an air/gas-driven tool when new dryness-indicating material is required. The invention additionally contemplates an alternative air/gas dryness indicator that is implemented by way of an electromechanical moisture detector and a numeric display that displays such air/gas dryness parameters as relative humidity, dew point temperature, or both. The invention likewise contemplates the use of additional numeric displays for indicating other compressed air/gas characteristics, such as flow, temperature, pressure and possibly pH.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of exemplary embodiments of the invention, as illustrated in the accompanying Drawings in which:
a is an enlargement of the partial cross-sectional view of the indicator cartridge of
Turning now to the drawings, wherein like reference numerals indicate like elements in all of the several views,
Turning now to
As an alternative to using the desiccant 48, a moisture sensitive paper that turns color according to the surrounding moisture content could be used. For example, as is conventionally known, when Bromide salts are distributed on litmus paper, a color change from light lime green to deep yellow will be exhibited as the relative humidity increases in the air/gas to which the paper is exposed. The relative humidity level at which this color change occurs can be formulated according to the distribution of the Bromide salt material on the paper. This implies that the moisture indicating characteristics of the paper can be adjusted according to the application. Thus, for tools requiring very dry air, the moisture sensitive paper could be designed so that the color change occurs at a low relative humidity threshold, such as about 10-20%. Higher relative humidity thresholds could be used for tools that are not as sensitive to moisture. It will be appreciated that other known varieties of moisture sensitive paper may also be used to produce different colors at different levels of moisture content.
In the event that moisture sensitive paper is used in lieu of the desiccant 48, the manner in which it is applied to the indicator cartridge 30, as well as the construction of the cartridge itself, can be varied in a number of ways. One technique would be to spray the moisture sensitive paper in particulate form onto the inside of the vessel 38, along with a suitable adhesive agent. Another technique would be to roll a sheet of the moisture sensitive paper into a tube and insert it into the vessel 38. A further option would be to spray or otherwise affix the moisture sensitive paper to a solid substrate that is then placed in the vessel 38, such as a flat plate, a disk, a cylinder, a sphere, etc. A further exemplary cartridge construction featuring moisture sensitive paper is discussed in detail below with reference to
The first and second ends 40 and 42 of the vessel 38 are capped by a pair of air/gas-permeable closures 50 that contain the desiccant 48 in the vessel 38 and also perform a filtering function. Each of the closures 50 is formed by a domed screen 52 and a peripheral member 54. The screens 52 extend substantially across the entire cross-sectional area defined by the ends 40 and 42 of the vessel 38, and must thus be permeable to the air/gas stream passing through the indicator cartridge 30. The screen 52 can be made from any suitable air/gas permeable material provided it is also strong enough to perform its function of retaining the desiccant 48 within the containment chamber 46. A perforated metal sheet made from stainless steel or the like, or a metal weave, is preferred. A sieve size of about 50 mesh may be used if the dryness indicating material 48 comprises silica gel beads. This sieve size is sufficiently small to trap desiccant bead particles that can be produced on the outlet end of the indicator cartridge 30 should the beads fracture and break apart during use of the indicator cartridge 30, yet is not so small as to produce unwanted pressure drop. Thus, the closure 50 at the outlet end of the indicator cartridge 30 will function as an after filter. At the inlet end of the indicator cartridge, the closure 50 will help pre-filter unwanted particulates such as dirt and oil.
The peripheral member 54 of each closure 50 can be made from various materials, including silicone rubber, plastic, etc. The peripheral member 54 are generally ring shaped, and may also comprise annular stub portions 55 that extend into the vessel 38 a short distance, if a seal needs to be maintained with first and second ends 40 and 42 of the vessel. The peripheral members 54 can be attached to the vessel 38 in any suitable fashion, such as by way of adhesive bonding, heat bonding, etc. It would also be possible to integrally form the peripheral members 54 as part of the vessels first and second ends 40 and 42. In that case, however, a means would needed to introduce the dryness-indicating material into the containment chamber 46. Each peripheral member 54 can be secured to the periphery of its associated screen 52 by molding the former in the presence of the screen.
It will be observed that the screens 52, due to their domed shape, each form a protuberance or central raised portion on an inner side thereof that extends into the containment chamber 46 of the vessel 38. The domed shape of each screen 52 likewise forms a plenum-defining cavity on an outer side thereof facing away from the containment chamber 46. Although the screens 52 are shown to be generally rounded in
Minimizing pressure drop is an important goal when it is considered that the tool 10 is primarily intended to be used in a compressed air/gas system that already incorporates a conventional filter/dryer in the compressed air/gas line. The existing filter/dryer will normally produce its own pressure drop, and its output pressure may not be significantly higher than what is required by the tool 10. In a painting application, for example, an HVLP (High Volume Low Pressure) spray guns require a minimum pressure of 30-40 psi in order to operate properly. The indicator cartridge 30 must be capable of delivering air or gas at the required pressure, and every effort must be made to avoid reducing the line pressure significantly below what is provided to the inlet side of the cartridge. By virtue of the domed configuration of the screens 52, the indicator cartridge 30 is able to function as a low-pressure-drop dryness indicator apparatus within the tool 10.
The indicator cartridge 30 is designed to be inserted into the cavity 32 through an access port 56 at the bottom of the housing 36. Following insertion of the indicator cartridge 30 through the access port 56, a spacer 58 of generally tubular configuration can be inserted to insure that the indicator cartridge 30 is properly seated within the cavity 32. The spacer 58 also provides an additional plenum at the inlet side of the indicator cartridge 30 to further distribute the compressed air/gas flowing through the desiccant 48 and reduce pressure drop. A removable closure in the form of a retainer fitting 60 is used to cap the access port 56 once the indicator cartridge 30 and the spacer 58 are inserted therein. The retainer fitting 60 is generally tubular in shape and is provided with a central bore 61 to pass compressed air/gas into the cavity 32. A first threaded portion 62 comprising a male thread pattern engages a corresponding female thread pattern formed at the access port 56. A second threaded portion 64 has a male thread pattern that engages a corresponding female thread pattern (not shown) formed in the fitting “F” of the hose line “L” (see
Once the indicator cartridge 30 is disposed in the cavity 32, and properly positioned by the spacer 58, the desiccant 48 will be visible externally of the tool 10 by virtue of an opening 70 formed in the wall of the housing 36. This opening defines the view port 28 of
During operation of the tool 10, compressed air or gas will flow into the cavity 32 through the central bore 61 of the retainer fitting 60 seated in the access port 56. The compressed air/gas will enter the area of the spacer 58, which allows the air/gas to disperse cross-sectionally before entering into the indicator cartridge 30 through the (pre-filtering) end closure 50 disposed at the inlet end 42 of the vessel 38. As the compressed air/gas passes through the desiccant 48, this material will respond according to the moisture content of the air or gas. For example, if the desiccant 48 comprises cobalt salt-treated silica gel beads, a deep blue color will indicate that the compressed air/gas is at a satisfactory dryness level, whereas a pink or magenta color will indicate an unsatisfactory dryness level. The compressed air/gas will continue out the (after-filtering) end closure 50 disposed at the outlet end 40 of the vessel 38, and into the flow passage 34, where it is utilized according to the conventional mechanics of the tool 10 (e.g., to deliver paint to be sprayed in a paint gun embodiment of the tool). Because of the positioning of the view port(s) 28 provided by the opening(s) 70, the state of the desiccant 48 can be regularly monitored by the user. In the event that the desiccant 48 does indicate a moisture problem, the user can stop the application and address the problem, thereby greatly reducing the risk of a compromised application, such as a fouled paint job. In most cases, when the moisture problem is corrected and there is a resumption of dry air/gas flow, the desiccant 48 will return to it original color.
After many wet/dry cycles, the performance of the desiccant 48 will degrade, and the desiccant will eventually lose its effectiveness. Moreover, the pre-filtering and after-filtering end closures 40 and 42 of the indicator cartridge 30 will at some point become clogged to the extent that pressure drop becomes excessive. To remedy these conditions, the indicator cartridge 30 is designed as a replaceable active element that can be easily changed out from time to time during the operational life of the tool 10. Promptly replacing the indicator cartridge 30 when problems arise will help ensure that the tool 10 remains in top operating condition.
Turning now to
Turning now to
In either of the embodiments of
Although each of the tools 10, 100, 200 and 300 of the above-described embodiments can be attached to a conventional compressed air/gas hose line extending to a conventional filter/dryer system, a tool according to the present invention can also be mounted to the end of a flexible in-line, point-of-use filter/dryer of the type disclosed in the above-referenced provisional application Ser. No. 60/553,163, and which is further disclosed in copending, commonly-owned regular application Ser. No. ______. The latter application is entitled “Flexible, Inline Point-Of-Use Air/Gas Dryer,” and was filed on even date with the present application. The contents of provisional application Ser. No. 60/553,163 and regular application Ser. No. ______ are both fully incorporated herein by this reference.
As shown in
Accordingly, a compressed air/gas-driven tool with an integrated dryness indicator has been disclosed according to several exemplary embodiments. The disclosed embodiments of the invention serve an important need in the art of compressed air driven tools, particularly paint spray guns, for users to be apprised of important information concerning the quality of the compressed air/gas being delivered to the tool. In conventional compressed air/gas delivery systems, the user does not know the condition of the delivered compressed air or gas at the point of use in a handheld tool. In a painting application, this deficiency carries the risk of a fouled application as a result of moisture being inadvertently applied along with the paint. The present invention addresses this problem in a low cost effective way. Moreover, by virtue of the replaceable nature of the indicator cartridge, which is the active element of the
It should be understood that the description and the drawings herein are merely illustrative, and it is contemplated that various modifications, combinations and changes can be made thereto without departing from the scope of the invention. Moreover, although the tools described herein have been exemplified as a paint gun, other air/gas-driven tools, such as drills, screw drivers, staplers, nailers, die grinders, chisels, impact wrenches and ratchets, sand blasters and sanders, as well as inflation (e.g., tires) devices, could be used with an integrated dryness indicator in accordance with the invention. As such, the invention is not to be in any way limited except in accordance with the spirit of the appended claims and their equivalents.
This application claims benefit of the filing date of U.S. Provisional Application No. 60/581,891, filed on Jun. 22, 2004. This application also claims benefit of the filing date of U.S. Provisional Application No. 60/553,163, filed on Mar. 15, 2004.
| Number | Date | Country | |
|---|---|---|---|
| 60581891 | Jun 2004 | US | |
| 60553163 | Mar 2004 | US |
