U.S. patent number 3,633,828 [Application Number 05/003,889] was granted by the patent office on 1972-01-11 for spray gun.
This patent grant is currently assigned to Graco Inc.. Invention is credited to James H. Larson.
United States Patent |
3,633,828 |
Larson |
January 11, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
SPRAY GUN
Abstract
An improved airless spray gun suitable for fine finish spraying.
The spray gun includes a body with a spray nozzle assembly secured
to its forward end. The nozzle assembly houses a valve assembly and
more particularly a valve seat of special shape and location and a
needle designed to cooperate with the seat. Contact between the
valve seat and the needle defines a closed position, whereas the
needle and seat may be moved relatively apart to an adjustably
controlled open position, permitting paint or other fluid under
pressure to flow at an adjustable controlled flow rate through an
annular passageway between the valve seat and the needle, to be
formed by the shape and location of the parts into a thin annular
cone-shaped sheet, with its vertex impinging at a spray nozzle
opening, and to be forced through the nozzle and atomized thereby
producing a spray pattern suitable for fine finish spraying.
Inventors: |
Larson; James H. (Amoka,
MN) |
Assignee: |
Graco Inc. (Minneapolis,
MN)
|
Family
ID: |
21708084 |
Appl.
No.: |
05/003,889 |
Filed: |
January 19, 1970 |
Current U.S.
Class: |
239/412;
239/DIG.14; 239/600; 239/526; 251/903 |
Current CPC
Class: |
B05B
9/01 (20130101); B05B 12/0026 (20180801); B05B
1/306 (20130101); Y10S 251/903 (20130101); Y10S
239/14 (20130101) |
Current International
Class: |
B05B
1/30 (20060101); B05B 9/01 (20060101); B05B
9/00 (20060101); B05b 007/12 () |
Field of
Search: |
;239/526,600,525,412,583,127,581 ;251/DIG.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wood, Jr.; M. Henson
Assistant Examiner: Culp, Jr.; Thomas C.
Claims
What is claimed and desired to be secured by United States Letters
Patent is:
1. An improved airless spray gun comprising:
a body;
a spray nozzle assembly secured to said body wherein said spray
nozzle assembly includes;
a passageway extending through said spray nozzle assembly having
one end in communication with a source of liquid under
pressure,
a nozzle opening having a center in communication with the other
end of said passageway,
a needle member having a tapered surface adapted for cooperation
and engagement with a tapered surface of a valve port, said tapered
surface of said needle member defining a needle angle,
a seat member positioned in said passageway between the ends
thereof housing said valve port whose tapered surface defines a
seat angle, said seat member positioned in said passageway such
that the projected extension of the tapered surface of said needle
member converges and intersects at approximately the center of said
nozzle opening when said needle member is in contact with the
tapered surface of said valve port,
a chamber extending from said seat member to said nozzle opening;
and
means for moving said needle member into contact and out of contact
with the tapered surface of said valve port thereby defining a
closed position and an open position respectively of said needle
member.
2. The improved airless spray gun of claim 1 wherein the end of
said chamber extending from said seat member is substantially
greater in cross-sectional area than said valve port and the other
end converging toward and conforming to said nozzle opening.
3. The improved airless spray gun of claim 1 wherein said means for
moving said needle member into contact and out of contact with the
tapered surface of said valve port includes a stop member for
limiting the rearward movement of said needle member out of contact
with the tapered surface of said valve port and thereby the size of
the opening between said needle member and the tapered surface of
said valve port.
4. The improved airless spray gun of claim 3 wherein the
longitudinal position of said stop member is adjustable thereby
causing the rearward movement of said needle member and the opening
between said needle member and the tapered surface of said valve
port to be adjustable to thereby accommodate different sizes of
nozzle openings at optimum conditions.
5. The improved airless spray gun of claim 4 wherein said means for
moving said needle member into contact and out of contact with the
tapered surface of said valve port further includes a trigger means
operatively connected with said needle member for moving said
needle member rearwardly out of contact with the tapered surface of
said valve port and against said stop member.
6. An improved airless spray gun comprising:
a body;
a spray nozzle assembly secured to said body wherein said spray
nozzle assembly includes;
a passageway extending through said spray nozzle assembly having
one end in communication with a source of liquid under
pressure,
a nozzle opening in communication with the other end of said
passageway,
a seat member positioned in said passageway between the ends
thereof housing a tapered valve port whose tapered surface defines
a seat angle,
a chamber extending from said seat member to said nozzle
opening,
a needle member in cooperation with said tapered valve port whose
tapered surface defines a needle angle, said needle angle being
greater than said seat angle; and
means for moving said needle member into contact and out of contact
with said seat member thereby defining a closed position and an
opened position of said needle member, said seat member being
positioned such that the projected extension of the tapered surface
of said needle member converges to a point as said nozzle opening
when said needle member is in said closed position.
7. The improved airless spray gun of claim 6 wherein said needle
member has a maximum value of 30.degree. and a minumum value of
10.degree. and wherein said seat angle has a maximum value of
20.degree. and a minimum value of 9.degree..
8. The improved airless spray gun of claim 7 wherein said needle
angle is about 12.degree. and said seat angle is about
10.degree..
9. An improved airless spray gun comprising:
a body;
a spray nozzle assembly secured to said body wherein said spray
nozzle assembly includes;
a passageway extending through said spray nozzle assembly having
one end in communication with a source of liquid under
pressure,
a nozzle opening in communication with the other end of said
passageway,
a seat member positioned in said passageway between the ends
thereof housing a tapered valve port whose tapered surface defines
a seat angle,
a chamber extending from said seat member to said nozzle
opening,
a needle member in cooperation with said tapered valve port whose
tapered surface defines a needle angle;
means for moving said needle member into contact and out of contact
with said seat member thereby a closed position and an open
position of said needle member, said seat member being positioned
such that the projected extension of the tapered surface of said
needle member converges to a point at said nozzle opening when said
needle member is in said closed position and said seat member and
said needle member defining an annular cone-shaped passageway when
said needle member is in said open position which is sufficient in
length to form the fluid passing therethrough into an annular
cone-shaped sheet.
10. The improved airless spray gun of claim 9 wherein said means
for moving the needle member into contact and out of contact with
the seat member adjustably controls the flow rate of the liquid
passing through said annular cone-shaped passageway.
11. The improved airless spray gun of claim 9 wherein the length of
said cone-shaped passageway is at least twice the diameter of said
valve port.
12. The improved airless spray gun of claim 11 having an annular
opening located at the entrance to said annular cone-shaped
passageway wherein the cross-sectional area of said annular opening
is substantially equal to the cross-sectional area of said nozzle
opening.
13. The improved airless spray gun of claim 12 having means to
provide for the adjustment and control of the size of the
cross-sectional area of said annular opening so as to accommodate
any size of nozzle opening.
14. The improved airless spray gun of claim 13 wherein said annular
cone-shaped sheet impinges at said nozzle opening to generate a
soft spray suitable for fine finish spraying.
15. An improved spray gun suitable for the airless spraying of
liquids such as paints comprising:
a body;
a spray nozzle assembly secured to said body including,
a nozzle opening extending through one end of said spray nozzle
assembly and being elongated in cross section,
a chamber in communication with said nozzle opening having a
cross-sectional area at one end substantially greater than the
cross-sectional area of said nozzle opening,
a seat member defining one end of said chamber and containing a
tapered valve port having a lateral surface which converges in the
direction of said nozzle opening and defines a seat angle, and
a conical member suitable for insertion into said valve port having
a tapered side which converges in the direction of said nozzle
opening to define a conical angle, said conical angle being greater
than said seat angle,
means for moving said conical member into and out of contact with
said seat member thereby defining a closed position and an open
position of said conical member;
an entrance passageway associated with a source of liquid under
pressure and in communication with said valve port;
an annular cone-shaped passageway extending through said entrance
passageway within said chamber to allow for the passage of said
liquid through said annular cone-shaped passageway in the form of
an annular cone-shaped sheet which impinges at the entrance of said
nozzle opening;
an annular opening at the entrance of said annular cone-shaped
passageway when said conical member is in said open position having
an optimum cross-sectional area substantially equal to the
cross-sectional area of said nozzle opening;
means to predetermine and to control the cross-sectional area of
said annular opening so as to accommodate any size of said nozzle
opening.
16. An improved airless spray gun comprising:
a body;
a spray nozzle assembly secured to said body wherein said spray
nozzle assembly includes;
a passageway extending through said spray nozzle assembly having
one end in communication with a source of liquid under
pressure,
a nozzle opening in communication with the other end of said
passageway,
means positioned in said passageway between the ends thereof for
directing at least two portions of the liquid along converging
paths so that said portions intersect at the entrance of said
nozzle opening,
means for adjustably controlling the flow rate of the liquid
portions which intersect at said nozzle opening.
17. An improved airless spray gun comprising a body with a
passageway therethrough for fluid to be sprayed, means for
connecting a high pressure fluid source to one portion of the
passageway, a nozzle portion having a spray opening communicating
with said passageway, and a valve assembly in said passageway close
to said spray opening, said valve assembly comprising a valve body
portion having a valve seat opening therein and a needle valve
portion movable axially within said valve seat opening between a
closed position in which the needle valve portion closes the valve
seat opening and passageway and a restricted open position
providing for accelerated linear movement of fluid from said
passageway through said valve seat opening to said spray opening,
at least one of said valve body and needle valve portions having a
surface guiding the fluid into a thin annular sheet converging to
an apex at said spray opening.
18. A spray gun according to claim 17 in which said valve body
portion and needle valve member have cooperating axially extending
conical surfaces providing an annular conical passageway
therebetween when the valve member is in open position, at least
one of said conical surfaces converging toward a vertex at said
spray opening and the conical surface of at least said needle valve
member terminating at a point spaced axially from said spray
opening thereby providing a region of fluid turbulence between the
spray opening and the annular conical valve passageway, aid region
being located within a conical area defined by the projection of
said surface of the valve body toward said spray opening.
Description
BACKGROUND OF THE INVENTION
This invention relates to an airless spray gun and more
specifically to an improved airless spray gun suitable for the fine
finish spraying required by many articles of manufacture.
It has long been recognized that there are two basic methods of
paint spraying, air spraying and airless spraying. In air spraying,
small particles of paint are entrained in a high velocity flow of
air through a spray nozzle with the air helping to atomize and
propel the paint against the surface to be painted. With air
spraying, a spray pattern of uniform density having a feathered
edge can be obtained on almost any type of surface. The uniform
density makes air spraying desirable for fine finish spraying while
the feathered edge permits a uniform coating to be applied to the
entire surface to be painted by overlapping the feathered edge
portions on subsequent parallel sweeps of the spray gun. The
principal disadvantage in air spraying is a result of the escape of
the air used to entrain and atomize the paint. This air carries
with it a substantial amount of paint and paint solvents resulting
in excessive waste and dangerous conditions due to the presence of
the inflammable particles remaining in the air. Thus, although the
desired spray pattern is obtainable from air spraying, the cost is
high in terms of waste and the need for adequate ventilation.
In airless spraying, paint is delivered under high pressure to an
atomizing nozzle where it is accelerated to a high velocity and
propelled toward the surface to be painted. The main advantage of
airless spraying is the absence of the "over spray" (loss due to
the escape of paint-saturated air) present in air spraying. This
substantially reduces the waste and minimizes the need for
ventilation of the air away from the area where the paint is being
applied. Although the disadvantages of air spraying are overcome by
airless spraying, the resulting spray pattern has been inferior,
being of nonuniform density having thickened areas or "pigtails"
and lacking the desired feathered edge. These qualities have made
the airless spray pattern unsuitable for fine finish spraying.
One prior proposal to eliminate the undesirable spray pattern in
airless spraying involves positioning a preorifice upstream from
the final spray nozzle, with an expanded chamber between the
orifice and nozzle. It was suggested that such an orifice have
substantially the same cross-sectional area as the final nozzle
opening, and that it should be a circular bore of uniform cross
section positioned between the pressurized paint source and the
final spray nozzle. A major limitation of such a preorifice was the
suggestion that it must be changed to accommodate different sizes
of nozzle openings. Even then optimum conditions are difficult to
realize since variables other than the preorifice-- spray nozzle
ratio are present, e.g., paint viscosity and density, temperature
and the flow pattern downstream from the preorifice. Thus, such a
structure requires many different sizes of preorifice inserts to
provide optimum conditions for different sized nozzle openings
having varying operating conditions.
Needle valves heretofore have been used to control the fluid flow
in airless spray guns but have not been acceptable for fine finish
spraying. This is apparently a result of the prior art not
recognizing the structure and dimensions necessary to produce the
proper fluid phenomena at the nozzle opening. In fact, it has been
observed that needle valves, as they exist in the prior art airless
spray guns, have not been used effectively for fine finishing even
with the addition of a preorifice and expanded chamber as suggested
above.
SUMMARY OF THE INVENTION
In contrast to prior airless spray guns of the type suitable for
fine finish spraying, the improved gun of the present invention
makes it possible to adjustably control the rate and type of flow
entering the spray nozzle opening, so as to accommodate any size of
nozzle opening at optimum conditions. Moreover, unlike prior spray
guns, it eliminates the need for a preorifice and an on-off valve
upstream from the preorifice since the improved needle valve of the
present invention serves as both an on-off control and as a means
of generating an improved fluid flow pattern prior to passage
through the nozzle opening. One result of such a flow pattern is
the formation of a soft spray having a uniform density with the
desired feathered edge.
More particularly, the improved spray gun of the present invention
includes a spray nozzle assembly which is adapted to be secured to
the forward portion of a body. The spray nozzle assembly includes a
spray tip housing a nozzle opening, a pressurized pain chamber and
a valve assembly positioned therebetween. The valve assembly is
arranged so that the seat portion containing a tapered valve port
and the needle portion designed to cooperate with the tapered valve
port are in coaxial relation to the nozzle opening. The needle,
when in contact with the valve seat, prevents the passage of fluid
through the valve port thereby defining a closed position. When the
needle is retracted by means located in the body of the gun, an
annular cone-shaped passageway is formed between the valve seat and
the needle through which the paint from the pressurized chamber
flows. The size of the cone-shaped annular opening is adjustably
controlled by a threaded stop associated with the needle retraction
means thereby allowing the annular opening and thus the flow rate
to be "tuned in" to optimum flow conditions for each size of nozzle
opening.
As the paint flows through the annular passageway, it is formed
into an annular cone-shaped sheet. Applicant has discovered that
the distance between the nozzle opening and the valve assembly when
properly related to the angles which the tapered orifice and the
needle side make with the spray nozzle axis causes the annular
cone-shaped sheet to impinge at the nozzle opening. This
impingement creates the flow phenomena necessary to generate a soft
spray having a uniform spray pattern with feathered edges.
Accordingly, it is an object of this invention to provide an
improved spray gun with a needle valve assembly having a structure
and corresponding dimensions capable of forming an annular
cone-shaped sheet which impinges at the nozzle opening.
It is also an object of this invention to provide such an assembly
with an annular cone-forming opening whose cross-sectional area is
adjustable thereby capable of accommodating any size of nozzle
opening at optimum spray conditions.
A further object is to eliminate the need for a valve upstream from
the annular opening by accomplishing the functions of both the
valve and the annular opening with an improved needle valve
arrangement.
A further object is to provide a convenient means of controlling
the flow rate of the fluid, while still maintaining the critical
flow pattern thus assuring the soft spray.
These and other objects and advantages of the present invention
will become apparent upon reference to the following
specifications, drawings and appended claims.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of the improved spray gun.
FIG. 2 is an enlarged cross-sectional view of the spray nozzle
assembly.
FIG. 3 is an expanded cross-sectional view of the seat member 10
and the tapered needle showing their axial orientation to each
other.
FIG. 4 is an enlarged cross-sectional view of the forward end of
the spray nozzle assembly with the tapered needle in its closed
position.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, the improved airless spray gun
comprises a main body 10, a handle 11, a trigger 12 and a spray
nozzle assembly 14. A hook portion 15 is located at the top of the
main body 10 to hang the gun when it is not in use.
Spray nozzle assembly 14 is attached to the front end of the spray
gun and includes a tubular member 16 having internally and
externally threaded end portions 18 and 19 and central portion 48
having a diameter substantially greater than the end portions 18
and 19. As shown, the end 19 extends through an aperture 49 so that
the central portion 48 of the tubular member 16 tightly abuts the
front end 41 of the main body 10 with a gasket 46 positioned
therebetween. Lock nut 45 cooperates with the external threads of
the end 19 to secure the spray nozzle assembly 14 to the main body
10. Also, locator pin 40 extends between the central portion 48 of
the tubular member 16 and the front end of the stock 41 to align
the spray nozzle assembly 14 in its proper position.
Referring now to FIG. 2, the spray tip 21 located at the forward
end of the spray nozzle assembly 14 is characterized by the nozzle
opening 20 and the prenozzle chamber 22. Nozzle opening 20, being
elongated in cross section, and passing through the forward end of
the spray tip 21, is in communication with the prenozzle chamber
22, chamber 22 having the end with a cross-sectional area
substantially greater than that of the nozzle opening 20 and a
tapered side 24 converging in the direction of the nozzle opening
20 and conforming to the shape thereof to guide the paint flowing
through a valve assembly 25 to the nozzle opening 20. The rearward
end of spray tip 21 abuts a portion of the seat member 26 and the
cylindrical member 28 with a sealing gasket 30 positioned
therebetween, all of which are secured tightly by the tip body 29.
The tip body 29 is in turn held secure by the annular cap 35 having
internal threads in cooperation with the external threads of the
end portion 18, and a flanged portion 49 engaging a shoulder
portion 31 of the tip body 29. The annular cap 35, and thus the
spray tip 21, are easily removed when it is necessary to change to
a spray tip 21 with a different size of nozzle opening 20.
Generally cylindrical member 28 positioned immediately to the rear
of the spray tip 21 has its forward end abutting the spray tip 21
with a gasket 30 positioned therebetween, an externally threaded
rearward end being received into the end portion 18, and an inner
surface defining an axial cavity 36 housing a valve assembly
25.
The valve assembly 25 includes a seat member 26 held about its
periphery in a coaxial relation to the nozzle opening 20 by a
portion of the inner surface of the cylindrical member 28. A
tapered, coaxial valve port 54 is contained in the seat member 26
and a needle or conical member 38 is carried by the front end of an
axially extending valve stem 39. Member 38 has a tapered side 56
(FIG. 3) converging in the direction of the nozzle opening 20 and
terminating in one direction at a forward end 59 and in the other
direction at a point where the tapered side 56 intersects with the
outer surface of the valve stem 39. The forward end 59 of the
needle 38 does not converge to a point but rather is terminated to
form a substantially flat surface. As seen in FIG. 4, the forward
end 59 extends slightly past the forward end 27 of the seat member
26 when the needle 38 is in a closed position and to the rear of
forward end 27 when in an open position. Although the length of the
needle 38 from the shutoff point 55 to the forward end 59 is not
critical, it must be of sufficient length to form the fluid into an
annular cone shaped sheet. The valve stem 39 is guided by a
counterbore 47 in the central portion 48 of the tubular member 16
and extends through a seal 42 (FIG. 1) and a gland nut 44 which is
threaded at one end and secured to the tubular member 16 at the
other end 19. The valve stem 39 then continues past the trigger 12,
through a bore 58, and into contact with the sealing ring 57 where
it extends into a fluid motor chamber 93 which along with the
trigger 12, controls the movement of the valve stem 39 as
hereinafter more fully described.
The valve assembly 25 in FIG. 2 is arranged so that when the
trigger 12 is in its relaxed position, the needle member 38 is in
contact with the shutoff point 55 of the seat member 26. This
defines a closed portion of the needle member 38, thereby
preventing the paint, under pressure, in the axial cavity 36 from
flowing through the valve port 54. When the trigger 12 is moved
rearwardly, the valve stem 39 and the needle member 38 are likewise
moved rearwardly defining an open position, as designated by dotted
line 32, in FIG. 2 thereby permitting the paint, under high
pressure, to flow at a high velocity from the axial cavity 36,
through the conical passageway 61 between the seat member 26 and
the needle member 38, and through the nozzle opening 20 whereby the
paint is atomized and sprayed onto the surface to be painted.
Valve port 54, as shown in FIG. 3, includes a tapered seating
surface 50, a tapered entrance surface 52, and a shutoff point 55
located at the intersection of surfaces 50 and 52, surfaces 50 and
52 further defining two valve port portions each having a shape
similar to the frustum of a cone. As shown, the seating surface 50
converges in the direction of the nozzle opening 20 with the
projected extension converging to a point and defining a seat angle
51. Applicant has discovered that the seat angle 51 is important in
producing the desired spray pattern for fine finishes having a
maximum value of about 20.degree., a minimum value of about
9.degree., and an optimum operating value of about 10.degree..
Likewise, the projected extension of the entrance surface 52
converges and defines an entrance angle 53 being substantially
greater than the seat angle 51. It is noted that the valve port
portion defined by surface 52 is not critical to the operation of
the valve assembly 25 in an effective airless paint sprayer, since
the paint sprayer will operate adequately with no entrance surface
52 at all. However, the presence of the surface 52 does improve the
efficiency of the spray gun by channeling the high pressure liquid
in the axial cavity 36 (FIG. 2) into the annular cone-shaped
passageway 61 (FIG. 4) and by allowing for better flow control at
the shutoff point 55.
As shown in FIG. 3, the tapered side 56 of the needle 38, if
extended, converges in the direction of the spray nozzle 20 to
define a needle angle 58 having a maximum value of about
30.degree., a minimum value of about 10.degree. and an optimum
value of about 12.degree.. The value of the needle angle 58 in FIG.
3 as compared to the seat angle 51 is important in that the two
angles cannot be equal. This angle difference is necessary to shape
the flow between the axial cavity 36 (FIG. 2) and the prenozzle
chamber 22 and to prevent the locking of the needle valve member 38
when the needle valve member 38 is in its closed position. In
addition, greater needle angle allows for the cross-sectional area
of the annular cone-shaped passageway 61, located between the
sealing surface 50 and the tapered side 56, to remain relatively
constant along its length, when the valve assembly 25 is in a
selected open position. Thus, the paint flowing through the
passageway 61 is maintained at a relatively constant velocity even
though the outer diameter of the annular cone-shaped passageway 61
is decreasing in the direction of the nozzle opening 20.
In FIG. 4, the distance D is shown to be that distance from the
nozzle opening 20 to the shutoff point 55. Applicant has found the
relation between the distance D and the needle angle 58 (FIG. 3) to
be of critical importance in creating the proper spray pattern for
fine finish spraying. He has discovered that the projected
extension of the tapered needle side 56 must converge to a point at
or near the nozzle opening 20 when the needle member 38 is in its
closed position, as shown in FIG. 4. This relationship allows the
liquid under high pressure in the axial cavity 36 to be accelerated
through the annular opening 23 between the tapered needle side 56
and the shutoff point 55 and to pass through the annular
cone-shaped passageway 61 causing the fluid to be formed into a
thin annular cone-shaped sheet which impinges at the nozzle opening
20. This impingement, in combination with the increased surface
area of the annular cone-shaped passageway 61, as compared to the
surface area of the circular bore in the prior art, creates the
desired fluid phenomena at the nozzle opening 20 to generate a soft
spray having a uniform spray pattern with feathered edges. In
addition, the adjustable valve assembly 25 makes it possible for
the fluid passing through the annular opening 23 to be accelerated
to the velocity at which it will pass through the nozzle opening
20. Applicant has found these conditions to be met when the
cross-sectional area of the annular opening 23 can be readily
adjusted to approximately equal the cross-sectional area of any
selected nozzle opening 20. The length of the annular cone-shaped
passageway 61 between shutoff point 55 and the front end of the
seat member 26 must also be sufficient in length to form the fluid
into a thin hollow cone-shaped sheet. Applicant has found a length
at least twice the diameter of the orifice opening to be
sufficient.
Note that in the preferred embodiment the annular opening 23
extends completely around the needle member 38. When liquid flows
through the opening 23, certain portions of the liquid intersect
with other portions so that the impinging force of each portion is
equally balanced by the impinging force of one or more other
portions. Thus, the preferred embodiment may be viewed as having at
least two portions of the liquid converging so that they intersect
at the nozzle opening 20.
Referring again to FIG. 1, the trigger 12 consists of a curved
metal casting 80 pivotally mounted at a point 81 and having a lower
portion 82 which can be swung toward and away from the handle 11,
thereby defining an open and closed position of the valve assembly
25. The trigger 12 can be moved freely except when the stop 84,
located on the forward edge of the handle 11, prevents such
movement. The stop 84 includes a neck member 85 containing
triangular teeth 86 which receive the member 88 and hold it in an
operating position, as shown in FIG. 1, or in a stop position, not
shown, where the member 88 is rotated 90.degree. from that shown in
FIG. 1. Coil spring 89 positioned on the inner side of the handle
11 biases the member 88 in cooperation with the teeth 86 and
prevents the member 88 from freely rotating about the neck member
85. In its operating position, member 88 fits between the side
portions 90 of the trigger 12 thereby allowing the trigger 12 to be
depressed. In its stop position, member 88 contacts the inside edge
91 of the trigger 12, preventing the trigger 12 from being
inadvertently depressed. The stop position allows the operator to
render the trigger 12 immobile when it is feasible to do so, for
example while cleaning the gun or replacing the spray tip 21,
thereby preventing possible injury to the operator.
As noted above, movement of the trigger 12 controls the flow of
paint through the valve assembly 25. In fact, the trigger 12
directly controls a pilot valve assembly 92 which in turn controls
the movement of the piston 94 located in the fluid motor and thus
controls the movement of the needle member 38. The piston 94 is
actually comprised of two disc members 95 and 96 threadedly mounted
on the rearward end of the valve stem 39 and a cup-shaped flexible
member 98 positioned therebetween, member 98 tightly abutting the
inner surface of a thin sidewall 99 thereby sealing the fluid motor
chamber 93. Secured to the rear side of the disc 96 is the sleeve
member 102 surrounded by a coil compression spring 104 having its
forward end abutting the rear side of the disc 96 with its other
end disposed against stop member 105. The compression spring 104
urges the piston 94 and thus the valve stem 39 in a forward or
valve closing direction (to the left as viewed in FIG. 1). When the
trigger 12 is depressed, the spring 104 is opposed by the pressure
of compressed air in chamber 93 to the left-hand side of piston
94.
Pilot valve assembly 92 noted above includes a valving element 120
within an axial bore 121 in an annular sleeve 122. Axial bore 121
has two diameters, one at 124 and one at 125, connected by a
sloping shoulder portion 126, and which is chamfered at 128
adjacent its inner end. When the operator releases the trigger 12,
coil spring 131 urges land 130 against the portion 128 thereby
preventing any compressed air from passing out of chamber 134
through passageway 132 and into fluid motor chamber 93. When the
trigger 12 is pulled back toward the handle 11, valving element 120
and thus land 129 is moved into contact with the sloping shoulder
portion 126 cutting off chamber 93 from the atmospheric air through
chamber 135. In turn, land 130 is moved away from the chamfered
portion 128 thereby permitting compressed air to pass from chamber
134, through passageway 132 and into chamber 93, urging the piston
94 and thus valve stem 39 toward an open position.
Stop member 105 includes a flanged portion 106 which serves as a
stop to prevent the sleeve 102 from being moved past a
predetermined position, as a base to contact coil spring 104, and
as a stop to prevent the stop member 105 from being removed from
its mounting in the wall chamber 108. Stop member 105 also includes
an externally threaded neck portion 109 and an end portion 110
designed to receive a control cap 111 housing a set screw 112 to
secure the cap 111 to the end portion 110. By turning the cap 111,
stop member 105 is moved along the wall member 108, as a result of
the threaded neck portion 109, determining the position of the stop
member 105. Stop member 105 in turn limits the movement of the
sleeve 102 and, likewise, the rearward movement of the valve stem
39 and the needle member 38. Thus, the optimum area of the annular
opening 23 is controlled by the position of the control cap 111,
thereby accommodating any size of nozzle opening 20.
To supply the paint under pressure to the axial cavity 36, the
conduit 115 communicates with the axial cavity 36 through the
lateral bore 114. One end of the conduit 115 is press fitted into
the outer end of the bore 114 and the other end terminates in a
fitting 118 adapted to interconnect the conduit 115 with the source
of paint under pressure, not shown. The fitting 118 in turn is
secured to the bottom portion of the handle 119 by the bracket
118.
The operation of the spray gun may be summarized by referring to
FIGS. 1 and 2. When the spray gun is not being utilized, the
trigger 12 is in a nondepressed position thereby allowing the coil
spring 104 to move the valve stem 39 and the needle member 38 in
the direction of the nozzle opening 20 causing the needle member 38
to contact the seat member 26 preventing paint from flowing through
the orifice 54. When the trigger 12 is depressed, the pilot valve
assembly 92 causes the piston 94 and the valve stem 39 to be moved
away from the nozzle opening 20 a predetermined distance which is
controlled by the position of the control cap 111. This movement
allows the paint, under high pressure in the axial cavity 36, to
flow through the cone-shaped passageway 61 in the form of a thin
annular cone-shaped sheet with its vertex impinging at the nozzle
opening 20 to generate a uniform airless spray pattern with a
feathered edge.
From the foregoing, it is apparent that the improved airless spray
gun includes a novel needle valve assembly capable of producing a
high velocity annular cone-shaped sheet. The valve assembly can
function both as an "on-off" valve and also as a means for
adjusting the annular cross section and rate of flow of the thin
conical sheet. The novel features allow the improved spray gun to
operate effectively as a fine finish sprayer and to eliminate many
of the disadvantages present in previous fine finish airless spray
guns.
The invention may be embodied in other forms not specifically shown
in the preferred embodiment without departing from the spirit or
essential characteristics thereof. The preferred embodiment is
therefore to be considered as illustrative only, with the scope of
the invention being indicated by the appended claims and their
equivalents.
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