Fluid sprinkling – spraying – and diffusing – Including supplemental gas shaping or shielding jet – Air shield surrounds projected airstream
Reexamination Certificate
2000-05-17
2001-07-31
Scherbel, David A. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Including supplemental gas shaping or shielding jet
Air shield surrounds projected airstream
C239S296000, C239S600000, C239SDIG001, C092S096000, C092S09800R, C277S634000
Reexamination Certificate
active
06267302
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention most generally relates to spray guns, both air atomizing and hydraulic pressure atomizing; and in particular, it relates to the shut-off/clean out needle mechanism of a spray gun and the use of a rolling wall diaphragm seal to isolate the shut-off valve needle from the needle actuator, and to quick disconnect components for servicing the front end and liquid chamber elements of the spray gun.
2. Background Art
Prior art
FIG. 1
details the mechanics of a conventional, air-atomized spray gun system, through which a source of liquid to be sprayed, and a source of compressed air, are emitted from a special nozzle in converging streams so as to cause the stream of liquid to be atomized by the air flow and projected in a precise pattern; permitting the controlled spray deposition of the liquid material onto a target surface.
The spray air and fluid are directed under pressure in converging streams so as to generate the atomized spray pattern. After use, a suitable solvent is typically run through the system for cleaning, further challenging the integrity of the seals. Common practice includes frequent partial disassembly, for cleaning and closer inspection of individual components.
Conventional atomizing spray gun designs include a liquid chamber and a tip section with an axial fluid outflow orifice and shut off needle, where the needle has a tapered or conical section that contacts the back of the fluid tip to close off the flow of the liquid being sprayed. The shut off needle can also have an extended tip end clean out section of uniform diameter, where the clean out portion of the needle protrudes through the fluid tip orifice when the needle is in the closed or sealed position.
The needle travels back and forth between the fully closed position, preventing flow of the liquid being sprayed, and the retracted or open position, allowing the liquid to flow out the nozzle. A biasing force in the shut off direction, sufficient to hold the needle forward, closed and sealed at all operating pressures, is provided by a spring on the aft end of the needle shaft. The actuating force to open the orifice and start the flow of liquid is provided by a piston attached to the needle shaft. The piston is located at the aft end of an air cylinder through which the needle shaft passes. When air is applied to the cylinder, the piston compresses the spring and pulls the needle away from the nozzle to permit liquid flow.
Between the liquid chamber and the air cylinder is an interference seal through which the needle shaft slides. This seal prevents the liquid from the liquid chamber from leaking along the needle shaft into the air cylinder. The interference seal is commonly an “O” ring, quad seal or a packing bushing that is intended to be resistant to the materials being sprayed, and the solvents commonly used for clean up. This simple and economical sealing method may be satisfactory for many spraying applications, but for liquids with a high adhesion rate or liquids with a high abrasion rate, these seals are likely to fail in a relatively shorter period of time. This is due to the fact that the seal cannot adequately wipe the needle clean as it cycles, allowing some of the liquid to pass into and by the seal and thereby cause premature failure of the seal.
Referring to prior art
FIG. 1
, the illustrated prior art spray gun
100
includes a nozzle section consisting of a fluid tip
101
and air cap
102
secured by collar
103
to body
104
. Spray liquid port
105
connects a liquid source to the liquid chamber and hence to fluid tip
101
. Spray air port
106
connects through internal passageways to air cap
102
. Axial metering and shut off needle
107
is operated between open and closed positions by single acting air cylinder and piston assembly
108
, and shut off biasing spring
109
. Needle opening port
110
connects to cylinder and piston assembly
108
. Needle shaft seals
111
and
112
, divided by vent
113
, isolate the liquid from the front end of spray gun
100
from the air cylinder and piston assembly
108
.
A close inspection of this and other prior art designs for atomizing spray guns discloses a further problem relating to how to best service the spray gun after use. The typical time required for break down, cleaning and/or maintenance, and re-assembly, is often a disincentive to good maintenance practices.
Other types of seals have been used in related devices and specialty spray guns to isolate the metering valve stopper and liquid chamber from the valve actuating mechanism. Kingsford's U.S. Pat. No. 5,695,120, is an airless spray gun for de-ionized water that provides continuous circulation of liquid from the liquid source through the gun between “on” periods of spraying. It has a valve stopper member that incorporates a diaphragm disk element for sealing the back wall of the liquid chamber from the trigger mechanism.
There are other classes of paint spraying devices. For example, airless paint sprayers utilizing direct pumping of paint with piston or diaphragm pumps are well known in the art. Such patents as Geberth's U.S. Pat. No. 4,768,932, a hydraulic paint pump; Wagner's U.S. Pat. No. 3,680,789, a spray gun with an electric vibrator and a diaphragm pump; and Juterbock's U.S. Pat. No. 5,863,184, a diaphragm pump for spraying high viscosity liquids, will provide context for some related materials.
Rolling wall diaphragms are commonly known to be used as seals in other types of piston and cylinder applications. Furon Company's WO98/02659 patent application for a double acting pneumatically driven rolling wall diaphragm pump is illustrative of this sealing technique.
In summary, there is clearly room for improvement in the art of atomizing spray guns, particularly as to the sealing of the needle shaft, and also in the provisions for disassembly and maintenance of the spray gun.
SUMMARY OF THE INVENTION
The invention, most simply stated, is a spray gun with novel shut off mechanism utilizing a rolling wall diaphragm seal to isolate the liquid chamber and shut-off needle from the needle actuator mechanism, and a quick disconnect housing coupling for opening the gun for cleaning and servicing. The diaphragm and diaphragm piston connect the needle valve to the needle valve operating piston while isolating the operating piston from the liquid as it is pumped through the liquid chamber and ejected from the nozzle as an atomized spray. The quick disconnect coupling provides for opening the gun for servicing and cleaning the liquid chamber, needle and diaphragm. In its sanitary coupling embodiment, it elates all pipe threads and threaded components from the nozzle body end of the gun.
It is an object of the invention to eliminate the internal sliding seals from the needle shaft in the liquid chamber of an atomizing spray gun. To this end, a rolling wall diaphragm and diaphragm piston have been introduced to replace the sliding seals of the prior art for sealing the needle operating piston from contact with the liquid being sprayed and the solvents used for cleaning.
It is a flier object to provide means for easy servicing and cleaning of the liquid chamber, needle and diaphragm face. To this end, the gun has front and rear housings which are assembled by a quick disconnect means such as an external quick disconnect nut or clamp.
It is yet a further object to provide an alternative to a fixed needle shut off spring which must over come the additional pressure exerted on a diaphragm and diaphragm piston. To this end, a double action needle valve operating piston is provided, with control air for both needle opening and needle closing functions.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein I have shown and described only a preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by me on carrying out my invention.
R
Asmus Scott J.
Ganey Steven J.
Moine Vernon C.
Scherbel David A.
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