Spray paint gun

A spray paint gun has an air passage interconnecting an air chamber of the gun body and the interior of a paint container, and a valve device for opening and closing the air passage. The gun body has a blind bore connected to the air passage. The air passage has a first section extending from the air chamber to the blind bore, a second section extending from the blind bore to the exterior of a connecting portion, and a third section formed in the wall of a tubular member which is connected to the gun body. The third section of the air passage intercommunicates the second section of the air passage and the interior of the container. The valve device includes a threaded bolt screwed to the blind bore. A threaded rod is threaded through a central hole of the threaded bolt. The threaded rod has a first end connected with a knob and a second end extending out of the threaded bolt into the blind bore of the gun body. The second end of the threaded rod has a central receiving blind hole. A coiled spring member is received in the central receiving blind hole. A disc has a central shaft which is inserted into the central receiving blind hole of the threaded rod.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a spray paint gun, more particularly to a spray 
paint gun which has a valve device for controlling the access of the 
compressed air into a paint container. 
2. Description of the Related Art 
Referring to FIG. 1, a conventional spray paint gun 1 includes an elongated 
gun body (1A) and a handle (1C) which is connected to a compressed air 
source (not shown). The gun body (1A) has a first air passage (1B) and a 
blind hole 4 extending longitudinally and inwardly from the front end of 
the gun body (1A). The first air passage (1B) is connected to the 
compressed air source via the handle (1C). Therefore, compressed air may 
be directed to the front end of the gun body (1A). A trigger 2 is provided 
pivotally on the gun body (1A) for controlling the air flow of the 
compressed air. An air cap (3A) with two air channels (3A') is mounted to 
the front end of the gun body (1A) by means of a screw nut (3B). An air 
chamber (3C) is formed between the front end of the gun body (1A) and the 
air cap (3A). The air chamber (3C) is communicated with the first air 
passage (1B). A nozzle 5 has a first end, which is threaded to the open 
end of the blind hole 4, and a tapered second end which is received in the 
air cap (3A). The nozzle 5 has a central through hole (5A) and a spray 
needle 1 received therein for opening and closing the central through hole 
of the nozzle 5, as best illustrated in FIG. 1A. A plurality of holes (5 
C) are formed in the tapered second end of the nozzle 5, which communicate 
the air chamber (3C) and the exterior of the gun body (1A). A connecting 
portion 6 has an externally threaded lower section (6B) which depends from 
a lower portion of the connecting portion 6. The externally threaded lower 
section (6B) of the connecting portion 6 is connected threadedly to an 
upper end of a tubular member 7. A paint container (T) is threaded to a 
lower end of the tubular member 7. The connecting portion 6 has a through 
bore (6A) that is communicated with the blind hole 4 of the gun body (1A). 
A pipe member 8 has a first end, which is inserted into the through bore 
(6A), and a second end which extends through the tubular member 7 and into 
the container (T). A second air passage 9 extends through the gun body 
(1A) and the connecting portion 6 in order to interconnect the air chamber 
(3C) and the interior of the container (T). The second air passage 9 has 
an internally threaded section (9B) adjacent to the air chamber (3C) and 
an outlet (9A) adjacent to the interior of the tubular member 7. The lower 
end of the tubular member 7 has a threaded hole (7A) in which a stop screw 
(7B) is threaded. 
When in use, the trigger 2 is actuated to allow compressed air to flow 
through the first air passage (1B) of the gun body (1A) and to the air 
chamber (3C). The compressed air flows out of the gun body (1A) from the 
air channels (3B') of the air cap (3A) and the holes (5C) of the nozzle 5, 
as best illustrated in FIG. A, which is an enlarged view of the encircled 
portion (A) in FIG. 1. A part of the compressed air flows into the paint 
container (T) via the second air passage 9. Thus, the internal pressure of 
the paint container (T) will be increased to a sufficient value, thereby 
forcing paint in the paint container (T) to enter the blind hole 4 through 
the pipe member 8 and the through bore (6A). The paint will further flow 
to the central through hole (5A) of the nozzle 5 and will be dispersed 
into mist by means of the compressed air which flows through the air 
channels (3B') of the air cap (3A) and the holes (5C) of the nozzle 5. 
Since the paint in the paint container (T) is directed to the blind hole 4 
of the gun body (1A) by means of the compressed air, a thicker paint may 
be used for spray painting. 
If a thinner paint is to be used for spraying painting, the paint may be 
siphoned from the paint container (T) to the central hole (5A) of the 
nozzle 5, as best illustrated in FIG. 2. In this situation, the compressed 
air should be prevented from entering the second air passage 9. This can 
be accomplished by removing the screw nut (3B), the air cap (3A) and the 
nozzle 5, in this sequence, from the front end of the gun body (1A). The 
stop screw (7B) is then threaded from the threaded hole (7A) and threaded 
into the internally threaded section (9B) of the second air passage 9. The 
nozzle 5, the air cap (3A) and the screw nut (3B) are mounted, in this 
sequence, to the front end of the gun body (1A). Thus, the compressed air 
will flow through the holes (5C) of the nozzle 5 and the air channels 
(3A') of the air cap (3A) and will not enter the second air passage 9. 
Therefore, the paint can be directed to the blind hole 4 and is released 
from the gun body (1A) by means of the pressurized air force or the siphon 
force by opening or closing the second air passage 9 with the use of the 
stop screw (7B). 
The conventional spray paint gun has the following disadvantages: 
(1) Insertion and removal of the stop screw (7B) into and from the threaded 
section (9B) are troublesome operations. 
(2) Since the stop screw (7B) is very small (the outer diameter and the 
length of the stop screw (7B) are both about 3 mm), the stop screw (7B) is 
liable to miss and can be damaged when threaded in the threaded section 
(9B) of the second air passage 9. 
SUMMARY OF THE INVENTION 
It is therefore a main object of this invention to provide a spray paint 
gun which has a valve device to open and close the second air passage. The 
valve device can be easily operated and will not miss and be damaged. 
Accordingly, the spray paint gun of this invention comprises an elongated 
gun body with a front end. A first air passage and a blind hole extend 
longitudinally and inwardly from the front end of the gun body. The first 
air passage is connected to a compressed air source. An air cap is mounted 
to the front end of the gun body and an air chamber is formed between the 
air cap and the front end of the gun body. The air chamber is communicated 
with the first air passage. A nozzle has a first end threaded to an open 
end of the blind hole of the gun body and a tapered second end received in 
the air cap. The nozzle has a central through hole and a spray needle 
received therein for opening and closing the central through hole of the 
nozzle. A connecting portion has an externally threaded lower section 
which depends from a lower portion of the gun body. The externally 
threaded section of the connecting portion is connected threadedly to a 
tubular member. A paint container is connected to the tubular member. The 
connecting portion has a through bore communicated with the blind hole of 
the gun body. A pipe member has a first end inserted in the through bore 
of the connecting portion and a second end extending through the tubular 
member into the interior of the container. The gun body further has a 
second air passage interconnecting the air chamber and the interior of the 
container and a valve device for closing and opening the second air 
passage. 
The gun body has a blind bore with a flat bottom connected to the second 
air passage. The blind bore has an internal thread. The second air passage 
has a first section extending from the air chamber to the bottom of the 
blind bore, a second section extending from the blind bore to the exterior 
of the connecting portion, and a third section formed in the wall of the 
tubular member. The third section of the second air passage 
intercommunicates the second section of the second air passage and the 
interior of the container. 
The valve device includes a threaded bolt with a shank, a head connected to 
the shank and a central hole formed through the head and the shank of the 
threaded bolt so that an opening is formed at the free end of the shank. 
The threaded bolt is screwed to the blind bore. The central hole of the 
threaded bolt has a first section which is adjacent to the head of the 
threaded bolt and which is provided with an internal thread, and a second 
section which has a diameter that is larger than the diameter of the first 
section of the central hole. The threaded bolt has a vent hole 
interconnecting the exterior of the threaded bolt and the second section 
of the central hole of the threaded bolt. A threaded rod is screwed to the 
first section of the central hole of the threaded bolt. The threaded rod 
has a first end connected with a knob and a second end extending out of 
the threaded bolt into the blind bore of the gun body. The second end of 
the threaded rod has a central receiving blind hole. A coiled spring 
member is received in the central receiving blind hole. A disc has a 
central shaft connected perpendicularly thereto. The central shaft is 
inserted into the central receiving blind hole of the threaded rod. The 
disc has a diameter this is smaller than the diameter of the blind bore of 
the gun body. The threaded rod is moved between a first position, wherein 
the second end of the threaded rod pushes the disc to abut the bottom of 
the blind bore in order to close the first section of the second air 
passage, and a second position, wherein the second end of the threaded rod 
abuts the free end of the shank of the threaded bolt in order to close the 
opening of the shank of the threaded bolt and wherein the disc abuts the 
bottom of the blind hole in order to close the first section of the second 
air passage by means of the biasing force of the coiled spring. 
Other features and advantages of this invention will become apparent in the 
following detailed description of a preferred embodiment of this invention 
with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 3 and 7 show a preferred embodiment of a spray paint gun 10 of this 
invention. The spray paint gun 10 includes an elongated gun body 11 and a 
handle 13 which is connected to a compressed air source (not shown). The 
gun body 11 has a first air passage 12 and a blind hole 15 extending 
longitudinally and inwardly from the front end of the gun body 11. An air 
cap 21 is mounted to the front end of the gun body 11 by means of a screw 
nut 22. An air chamber 14 is formed between the front end of the gun body 
11 and the air cap 21. A nozzle 17 has a first end threaded to the stepped 
open end 151 of the blind hole 15 of the gun body 11 and a second end 
received in the air cap 21. The nozzle 17 has a central through hole 171, 
as best illustrated in FIG. 7A. A connecting portion 16 has an externally 
threaded lower section 161 which depends from a lower portion of the 
connecting portion 16. The externally threaded lower section 161 of the 
connecting portion 16 is connected threadedly to a tubular member 30. A 
paint container 40 is threaded to the tubular member 30. The connecting 
portion 16 has a through bore 162 that is communicated with the blind hole 
15 of the gun body 11. A pipe member 8 has a first end which is inserted 
into the through bore 162 and a second end which extends through the 
tubular member 30 and into the container 40. The aforementioned structure 
of the spray paint gun 10 of this invention is similar to that of the 
conventional spray paint gun and is not the feature of this invention. 
A second air passage 18 extends through the gun body 11 and the connecting 
portion 16 in order to interconnect the air chamber 14 and the interior of 
the container 40. A valve device 70 is provided to close and open the 
second air passage 18. 
Referring to FIG. 6, the gun body 11 has a blind bore 183 with a flat 
bottom 184 extending to the second air passage 18. The blind bore 183 has 
an internal thread. The second air passage 18 has a first section 181 
extending from the air chamber 14 to the bottom 184 of the blind bore 183, 
a second section 182 extending from the blind bore 183 to the exterior of 
the connecting portion 16, and a third section 31 formed in the wall of 
the tubular member 30. The third section 31 of the second air passage 18 
intercommunicates the second section 182 of the second air passage 18 and 
the interior of the container 40. Referring to FIGS. 4 and 5, the valve 
device 70 includes a threaded bolt 71 with a shank 713, a head 712 
connected to the shank 713 and a central hole 711 formed through the head 
712 and the shank 713 of the threaded bolt 71 so that an opening 7111 is 
formed at the free end of the shank 713. The threaded bolt 71 is screwed 
to the blind bore 183. The central hole 711 of the threaded bolt 71 has a 
first section 714, which is adjacent to the head 712 of the threaded bolt 
71 and which is provided with an internal thread, and a second section 715 
which has a diameter that is larger than the diameter of the first section 
714 of the central hole 711. The threaded bolt 71 has a vent hole 716 
interconnecting the exterior of the threaded bolt 71 and the second 
section 715 of the central hole 711 of the threaded bolt 71. A threaded 
rod 72 is screwed to the first section 714 of the central hole 711 of the 
threaded bolt 71. The threaded rod 72 has a first end 724 connected with a 
knob 721 and a second end 725 extending out of the threaded bolt 71 into 
the blind bore 183 of the gun body 11. The second end 725 of the threaded 
rod 72 has a central receiving blind hole 723. A coiled spring member 73 
is received in the central receiving blind hole 723. A disc 74 has a 
central shaft 741 connected perpendicularly thereto. The central shaft 741 
is inserted into the central receiving blind hole 723 of the threaded rod 
72. The disc 74 has a diameter that is smaller than the diameter of the 
blind bore 183 of the gun body 11. The threaded rod 72 is moved between a 
first position, as best illustrated in FIG. 8, wherein the second end 725 
of the threaded rod 72 pushes the disc 74 to abut the bottom 184 of the 
blind bore 183 in order to close the first section 181 of the second air 
passage 18, and a second position, as best illustrated in FIGS. 9A and 9B, 
wherein the second end 725 of the threaded rod 72 abuts the free end of 
the shank 713 of the threaded bolt 71 in order to close the opening 7111 
of the shank 713 of the threaded bolt 71 and wherein the disc 74 abuts the 
bottom 184 of the blind hole 183 in order to close the first section 181 
of the second air passage 18 by means of the biasing force of the coiled 
spring 73. The opening in the free end of the threaded bolt 71 is in the 
shape of a truncated cone, while the second end 725 of the threaded rod 72 
is shaped correspondingly as a truncated cone. Therefore, when the 
threaded rod 72 is moved to the second position, the opening 7111 of the 
threaded bolt 72 can be closed in an air-tight manner. 
When the knob 721 is rotated clockwise in order to move the threaded rod 72 
to the first position, the second air passage 18 is blocked and the 
compressed air can not enter the paint container 40. Therefore, the paint 
in the paint container is siphoned from the paint container 40 to the 
central hole 171 of the nozzle 5, through the pipe member 50, the through 
bore 161 of the connecting portion 16 and the blind hole 15 of the gun 
body 11, as best illustrated in FIG. 8. The interior of the paint 
container 40 is communicated with the exterior of the paint container 40 
by means of the third section 31 of the tubular member 30, the second 
section 182, the central hole 711 and the vent hole 716 of the threaded 
bolt 71. 
When the knob 721 is rotated counterclockwise in order to move the threaded 
rod 72 to the second position, the second air passage 18 is blocked 
resiliently by the disc 74. The compressed air can enter the paint 
container 40 to force the thicker paint in the paint container 40 to flow 
to the central hole 171 of the nozzle 5, through the pipe member 50, the 
through bore 161 of the connecting portion 16 and the blind hole 15 of the 
gun body 11, as best illustrated in FIG. 9B. When the spray paint gun 10 
is not in use and the compressed air is not supplied thereto, the disc 74 
will block the first section 181 of the second air passage 18, and thus, 
the air pressure of the paint container 40 may be maintained at a high 
pressure value. Therefore, when the spray paint gun 10 is in use, there 
will be no pressure difference between the air chamber 14 and the paint 
container 40. No time lag will occur between two discontinuous 
applications of the spray paint gun 10 of the present invention. 
Note that the valve device 70 of this invention can be easily operated 
without damage to the valve device 70. In addition, since the second air 
passage 18 of this invention is formed with three short sections, these 
sections can be easily cleaned when blocked by paint. 
With this invention thus explained, it is apparent that numerous 
modifications and variations can be made without departing from the scope 
and spirit of this invention. It is therefore intended that this invention 
be limited only as indicated in the appended claims.