Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
204701 4
Air Valve For Portable Paint Gun
Backqround of the Invention
This invention pertains to the field of portable
painting equipment, more particularly to portable paint guns
referred to as high volume low pressure or HVLP type paint
guns. In the past, such guns have been characterized by
relatively complex and costly sealing mechanisms to prevent the
escape of pressurized air from the interior of such guns. The
present invention provides an improved apparatus for preventing
the escape of pressurized air in a simple and efficient
structure.
More particularly, there is provided an air valve for
use in combination with a portable paint gun of the type having
a control shaft for controlling a supply of pressurized air to
atomize a selectively provided stream of paint. The air valve
includes a generally cylindrical axially extending hub portion
having a through bore which interfits closely with the control
shaft of the paint gun. A radially outwardly projecting
support portion is mounted on the hub portion. A generally
conical outer rim portion extends coaxially with the hub
portion and is mounted on the support portion radially
outwardly of the hub portion. The conical rim portion has a
tapered sealing surface adapted for matingly interfitting with
a tapered valve seating surface in the gun. In operation, the
mating sealing and seating surfaces are in contact with each
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other when the control shaft is in a closed position and
further, the sealing and seating surfaces are axially spaced
from each other when the control shaft is displaced axially
from the closed position.
These features and their advantages will become
apparent from the following description and the appended
drawings.
Description of the Drawings
Figure 1 is a right side elevation view of the present
invention with parts cut away and with movable parts shown in
an OFF position.
Figure 2 is an enlarged side elevation detail of the
shaft seal of the present invention.
Figure 3 is an enlarged side elevation detail of an
air valve for the gun of the present invention.
Figure 4 is a fragmentary right side elevation view
as seen in Figure 1 with movable parts
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in an intermediate position.
Figure 5 is a fragmentary right side
elevation view with movable parts in an ON position.
Detailed Description
05 Referring now to the drawings and more
particularly to Figure 1, a portable paint gun 10 may
be seen. Gun 10 has a handle 12 which is preferably
hollow, and through which compressed air can pass
when connected to a source of compressed air via
fitting 14. Gun 10 further has a paint cup 16 having
a siphon tube 18 to draw paint out of paint cup 16 in
operation. Gun 10 further has a trigger 20 pivotably
mounted to a gun body 22 via a trigger pin 24.
Gun 10 further has an air cap 26 retained by
a locking ring 28 on body 22. An air cap spring 30
is preferably secured to a detent plate 32, as for
example, by spot welding. Detent plate 32 preferably
has projections 34, 36 which are retained
respectively in slots 38, 40 to prevent rotation of
plate 32. Plate 32 preferably has a cruciform
opening interdigitated with projections on plate 32
(not shown) which are received in mating recesses
(not shown) in air cap 26. The detents in plate 32
and recesses in cap 26 cooperate to hold cap 26 in
one of three predetermined positions to provide for
control of the paint pattern in a manner well known.
Gun 10 further has a fluid nozzle 42 which cooperates
with a needle 44 to form a needle or paint valve 46
to control the flow of paint or other material
delivered by gun 10. A needle packing nut 48 is
preferably threaded into body 22 to compress needle
packing 50 against needle 44.
Gun 10 also has an air passageway 52 in
communication with a plenum 54 surrounding fluid
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nozzle 42. Plenum 54 is in communication with recess
56 in air cap 26. Trigger 20 is in contact with an
air valve shaft 58 surrounding needle 44 and carrying
an air valve 60. An air plug 62 is preferably
05 threaded into body 22 to close off an alternative
inlet to passageway 52. In the configuration shown
in Figure 1, gun 10 is arranged for "non-bleeder"
operation. By interchanging plug 62 with fitting 14,
and supplying air directly to passageway 52, gun 10
would be configured for "bleeder" operation.
Valve 60 is retained on shaft 58 by a
retaining ring 64 on one side of valve 60 and by a
flange 66 (see Fig. 4) on the other side of valve 60. 'Jalve 60 is
urged toward a mating seat 68 by an air valve spring
70. Air valve spring 70 is also in contact with a
shaft seal 72. Shaft seal 72 seals shaft 58 against
a material adjustment housing 74 threaded into gun
body 22. A needle spring 76 is retained by a
material adjustment knob 78 threaded on housing 74
and spring 76 urges needle 44 forward against nozzle
42 to maintain needle valve 46 in a closed position.
A bushing 79 preferably formed of plastic
serves as a guide and air seal around shaft 58 and
holds shaft 58 and needle 44 in alignment during
assembly and operation of gun 10. It is to be
understood that bushing 79 need not be an "air-tight"
seal since it only needs to prevent air leakage along
shaft 58 when valve 60 is in the intermediate and ON
positions.
Referring now more particularly to Figure 2,
various details of the shaft seal 72 may be seen.
Seal 72 has a mediate portion 80 having a radially
outwardly projecting flange 82 and a generally
cylindrical interior recess 84 located radially
204 70 1 4
inwardly of the flange 82. Seal 72 further has a
first conical rim 86 extending axially in a first
direction away from flange 82 with a shallow conical
taper from a relatively thicker cross-section 88
05 proximal of the flange 82 to a relatively thinner
cross-section 90 distal of flange 82. Shaft seal 72
further has a first extension 92 of the generally
cylindrical interior recess 84 with extension 92
located radially inwardly of surface 86.
Seal 72 further has a second conical rim 94
extending axially in a second direction opposite the
first direction away from flange 82 and further has a
second extension 96 of the generally cylindrical
interior recess 84 extending axially along and
radially inward of rim 94.
Rim 94 of seal 72 has a conical inner
surface 98 extending from the second extension 96 of
the generally cylindrical interior recess 84 to a
cylindrical shaft sealing surface 100 which is
located axially distal of the flange 82 in the second
direction. Rim 94 also has a tapered sealing surface
102 having an external conical taper adapted for
contacting and interfitting with a mating
correspondingly tapered bore or chamfer 104 (s~e Fig. 4) in
element 74 of paint gun 10 such that shaft seal 72
prevents the passage of air between the control shaft
58 and the shaft sealing surface 100 and also from
between the sealing surface 102 and the tapered bore
104 when pressurized air is present in chamber 106 (see Fig. 1).
It is to be understood that first conical
rim 86 is sized to mate in an interference fit with
cylindrical compression spring 70 to retain seal 72
on spring 70 when gun 10 is disassembled. It is
further to be understood that spring 70 acts against
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flange 82 to urge seal 72 in the second direction
with respect to the control shaft 58. In a preferred
embodiment, the first conical rim 86 tapers from
0.228 inches diameter to 0.311 inches diameter and
05 the spring 70 has an internal diameter of 0.316
inches.
It is further to be noted that the tapered
sealing surface 102 of conical rim 94 preferably has
a taper substantially equal to a taper of the conical
inner surface 98 providing a constant cross-sectional
thickness of rim 94 between surfaces 98 and 102. It
is further to be understood that the cylindrical
interior recess 84, along with its extensions 92, 96
preferably has a diameter substantially greater than
the diameter of the control shaft around which the
seal 72 is located such that there is a radial
clearance between shaft 58 and recess 84, together
with its extensions 92, 96. Furthermore, the shaft
sealing surface 100 preferably has an axial length
that is relatively short with respect to the axial
length of the overall shaft seal 72 (e.g. less than
ten percent) such that the resistance to relative
axial movement between the control shaft 58 and the
seal 72 is minimized.
In a preferred embodiment, surface 100 is
0.025 inches long while seal 72 is 0.365 inches long
overall. Surfaces 98, 102 and 104 each preferably
have a conical taper of 30 degrees.
In operation, pressure from spring 70 forces
seal 72 against the tapered bore or chamfer 104 in
the material adjustment housing 74 creating an
airtight seal. Axial force or pressure generated by
spring 70 is transferred to a radial force by the
interaction of surfaces 102, 104 thus urging surface
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100 against shaft 58 (making use of the conical
flexibility of rim 94), forming an airtight seal. As
seal 72 wears at surface 100, seal 72 is permitted to
move axially in the second direction as urged by
05 spring 70 to maintain sufficient pressure to insure
sealing between shaft 58, seal 72 and housing 74.
Referring now more particularly to Figure 3,
various details of the air valve 60 may be seen.
Valve 60 has a generally cylindrical axially
extending hub portion 110 having a through bore 112,
a radially outwardly projecting support portion 114
mounted on the hub portion 110, and a generally
conical outer rim portion 116 extending coaxially
with hub portion 110 and mounted on support portion
114 radially outwardly of hub portion 110. Rim
portion 116 has a tapered sealing surface 118 adapted
for matingly interfitting with a tapered valve
seating surface 120 in the body 22 of gun 10. Valve
60 further has an axial recess 122 located in a
region radially inward of the tapered sealing surface
of rim portion 116. The hub portion 110 of valve 60
has a first shoulder 124 and a second shoulder 126
for locating the valve in first and second axial
directions on shaft 58. Shoulder 124 is held by
retaining ring 64 and shoulder 126 is held by flange
66 on shaft 58.
Both seal 72 and valve 60 are preferably
formed of a relatively resilient material such as
virgin polytetrafluorethylene as sold under the
trademark TEFLON by EI Dupont de Nemours Co. The
material of valve 60 is preferably homogeneous with
the rim portion 116 being relatively flexible with
respect to the hub and support portions 110, 114 such
that sealing surface 118 conforms to the seating
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surface 120 when valve 60 is drawn against the
seating surface 120. Surface 118 preferably has an
external conical angle 128 of 16 degrees, while
seating surface 120 preferably has an internal
05 conical angle 130 of 18 degrees.
Rim portion 116 provides a "forgiving"
alignment between seal 60 and seating surface 120.
The flexibility of rim portion 116 allows the tapered
sealing surface 118 to conform to radial and axial
misalignment between seal 60 and gun body 22.
Because angle 130 is greater than angle 128, a
leading edge 132 of the sealing surface 118 will
contact surface 120 first. It has been found
preferable that hub portion 110 and support portion
114 are relatively rigid with respect to rim portion
116 which is relatively conically flexible and
provides a secondary seal area along surface 118
distal of leading edge 132, thus compensating for
creep or cold flow of lip portion 116 during the
operating lifetime of gun 10. The rigidity of
support portion 114 also provides a radial clearance
protection of rim portion 116 to reduce the
possibility of damage during storage and handling of
valve 60 prior to assembly into gun 10.
Referring now to Figures 4 and 5, along with
Figure 1, the operation of the air valve and seal is
as follows:
In Figure 1, the gun is shown in an OFF
position with both the paint or needle valve 46 and
air valve 60 in a closed position. Paint valve 46 is
closed when needle 44 is its forwardmost position and
is contacting the interior of fluid nozzle 42. Air
valve 60 is in the closed position when control shaft
58 is in the forwardmost or closed position. With
2û4701 4
the gun configured for "non-bleeder" operation,
retracting trigger 20 from the OFF or closed position
shown in Figure 1 to an intermediate position as
shown in Figure 4, will move control shaft 58, but
05 not needle 44, thus opening passageway 52 to the
source of pressurized air by moving air valve 60 away
from seating surface 120 (see Fig. 3) pennitting the passage of
air therethrough. Further progression of trigger 20
from the position shown at Figure 4 to the position
shown in Figure 5 will move the control shaft 58
axially within seal 72 further in the second
direction causing the control shaft to drive needle
44 against spring 76 opening the needle valve 46.
Thus, it may be seen that in Figure 1, both
the paint valve 46 and the air valve 60 are in the
OFF position. In Figure 4, the air valve 60 is in
the ON position while the paint valve 46 remains in
the OFF position. In Figure 5, both the paint valve
46 and the air valve 60 are in the ON position.
It is to be understood that as trigger 20 is
released, the paint valve 46 will move to the OFF
position as shown in Figure 4, while the air valve 60
will remain ON, thus clearing paint from air cap 26
and the exterior of fluid nozzle 42. Further release
of trigger 20 will permit movement of control shaft
58 to the closed position for air valve 60 such that
the sealing surface 118 (see Fig- 3) conforms to the seating
surface 120 when t~e control shaft is in the closed
position of Figure 1. It can thus be seen that the
mating, sealing and seating surfaces 118, 120 are in
contact with each other when the control shaft 58 is
in a closed position and the sealing and seating
surfaces 118, 120 are axially spaced from each other
when the control shaft 58 is displaced axially away
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from the closed position. It is to be understood
that seal 72 maintains an air seal between itself and
control shaft 58 in each of the positions shown in
Figures 1, 4 and 5 and while shaft 58 is moving among
05 those positions.
The invention is not to be taken as limited
to all of the details thereof as modifications and
variations thereof may be made without departing from
the spirit or scope of the invention.
