Cleaning of spraying apparatus

For cleaning spraying apparatus, such as a spray gun, the spray outlet is sealingly coupled to a conduit coupling (possibly after removal of an air cap). Cleaning solvent is then passed through the gun and coupling, and is collected in a reservoir without being sprayed into the open air. For a pressure feed gun, the solvent is fed without the use of a compressed gas stream. The cleaning action may be enhanced by injecting air into the solvent adjacent its entry to the gun. Solvent (and injected air) may also be passed through the gun in reverse direction. The process may be automated, with the gun held in a housing with its trigger clamped open.

BACKGROUND OF THE INVENTION 
The present invention relates to the cleaning of spraying apparatus such as 
spray painting guns and similar equipment. In one aspect it relates to 
apparatus for use in such cleaning operations. In another aspect it 
relates to a method of cleaning. 
A conventional spray painting gun has respective inlets for supplies of 
compressed gas (usually air) and liquid paint. These are mixed at the 
outlet of the gun, and emerge as a fine spray. It is periodically 
necessary to clean the gun. The normal method used is simply to pass a 
cleaning solvent through the paint inlet, by filling the paint container 
with the solvent. The solvent is then sprayed in the same manner as paint, 
using the compressed gas supply. This is rather wasteful of both solvent 
and gas. Furthermore, the expelled solvent must be captured, since it will 
rarely be acceptable to spray it into free air. Normally a paint spray 
booth has means for trapping sprayed paint, often involving mixing the 
spray with water treated with a chemical additive. However, the usual 
additives are rendered ineffectual by the admixture of significant 
quantities of the cleaning solvent. Thus before the booth can be returned 
to paint spraying, the additive must be replaced, if the continued use of 
the booth is not to lead to an unacceptable residue and the eventual 
discharge of pollutants. 
A further disadvantage of the known technique is that the operator has to 
be present, holding the gun. 
GB-A No. 2 095 586 discloses means for cleaning a spray apparatus that uses 
a centrifugal atomiser. This is moved so that it can spray into a 
bowl-shaped receptacle, relative to which it must be carefully positioned. 
Some paint is likely to escape. The arrangement is rather cumbersome, and 
is only suitable for the particular type of spray apparatus. 
Preferred embodiments of the present invention allow some or all of these 
disadvantages to be ameliorated. 
SUMMARY OF THE INVENTION 
In one aspect the invention provides a cleaning assembly comprising conduit 
means adapted for coupling to a spraying outlet of a spraying means for 
conveying liquid passed through that outlet to a reservoir. 
The assembly may include a reservoir for cleaning liquid and means for 
conveying it to a spray liquid inlet of the spraying means. (The spray 
liquid inlet is the inlet for the liquid which the spraying means is 
normally used to spray, e.g. paint.) The conveying means may include a 
pump. The arrangement may be such that the cleaning liquid can be passed 
through the spraying means and out via the conduit means without the need 
for propulsion by a separate stream of compressed gas. The reservoir for 
cleaning liquid may be the same as the reservoir receiving liquid via the 
conduit, so that the liquid is recycled. It may be strained or otherwise 
cleaned before recycling. Alternatively there may be separate reservoirs 
(though the liquid may still be recycled, of course). There may be means 
for reversing the flow of liquid. 
The cleaning assembly may include the spraying means. 
In another aspect the invention provides a method of cleaning a spraying 
means which comprises coupling conduit means to a spraying outlet of 
spraying means and passing cleaning liquid through the spraying means to a 
reservoir, via the conduit means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 1, a conventional pressure feed spray painting gun 
10 has controls 12 for compressed gas and liquid, an inlet 14 for paint; 
an outlet region 16; and a trigger 18 which operates a needle valve which 
controls the outlet passage. For cleaning, the trigger 18 is held in the 
spraying position. In the FIG. 1 arrangement this has been achieved by 
mounting the gun on a bracket 20 comprising spaced rods (three in this 
example) which engage the trigger 18 and a handle 22 of the gun. Of 
course, a clip or manual pressure could be used. At the outlet region 16, 
a conduit 24 is coupled, by means described later. This passes to a 
reservoir 26, which is a container 28 with a sealed lid 30 with an air 
vent 31. An input conduit 32 (which may be the standard conduit used for 
supplying paint) passes to the paint inlet 14 from the input reservoir 34. 
As shown, this is a conventional pressure feed tank such as may be used 
for supplying paint under pressure (e.g. using compressed gas). 
Alternatively there could be a pump for conveying cleaning fluid along the 
conduit 32 to the gun 10. 
Referring now to FIG. 2, it can be seen that the outlet region 16 of the 
gun 10 has, adjacent the spray outlet, an external thread 36 on which is 
engaged a standard air cap retaining ring 38. This is being used to retain 
not the air cap (which is employed during paint spraying) but a special 
conduit coupling 40. This is a tubular bushing having an inner flange 42 
which is retained by the retaining ring 38. (Alternatively the conduit 
coupling may have a tubular extension with an internal thread which 
engages the thread 36 of the gun directly, without a separate retaining 
ring 38.) The coupling 40 also has an outer cylindrical portion over which 
an end of the conduit 24 may be sealingly passed, e.g. retained by a clip. 
The conduit coupling 40 may be a metal pressing or a plastics moulding, or 
could be machined from solid material. It is provided with a seal 44 
(suitably a ptfe O-ring) around its region 46 of abutment with the outlet 
of the gun so as to ensure fluid-tight coupling of the conduit 24 to the 
gun. (Since the cleaning liquid will generally be passed through the gun 
without the use of high pressure gas, it is an easy task to achieve an 
adequate seal.) 
Thus, when the gun 10 has been used for spraying paint and it is desired to 
clean it, it is a simple matter to remove its air cap and attach the 
conduit coupling 40, which may already be connected via the conduit 24 to 
the reservoir 26. The compressed air supply is closed off, and a supply of 
cleaning fluid is connected. This may be achieved by filling the reservoir 
34 used for paint with the cleaning fluid, or by connecting a separate 
reservoir, possibly via a separate, clean conduit 32. Cleaning fluid can 
then be passed through the gun via the conduit 32. It is never sprayed 
into the atmosphere, but is collected by the conduit 24 and passed to the 
reservoir 26. Of course this must communicate with the atmosphere so that 
excessive pressure does not build up. As shown in FIG. 1 the reservoir's 
inlet is screened from its air outlet by a baffle assembly 27 which in 
this example has the form of a hollow double cone. The upper and lower 
cones have mutually staggered apertures so that escaping air must follow a 
sinuous path. Entrained liquid is thus likely to be deposited on the 
baffles whence it runs down into the bottom of the reservoir 26. The 
reservoir 26 may have a maximum level detector and fluid cutoff device, so 
that the gun can be left to clean itself, the trigger being held open by 
the clip 20, without the operator being in attendance. 
Desirably, cleaning liquid is passed through the gun not only in the normal 
flow direction but also in the reverse direction. With the apparatus of 
FIG. 1 this can be achieved by exchanging the positions of the conduits 32 
and 24 on the paint inlet 14 and the conduit coupling 40 respectively. 
FIG. 3 shows an alternative system. Instead of two separate reservoirs 
26,34, there is one common reservoir 50. Each conduit 24,32 communicates 
with a like tube 52 which opens at a lower region of the reservoir 50 
within a respective strainer 54. At least one of the conduit/tube branches 
incorporates a pump 56. As shown, this is located between the outlet 
conduit 24 and its tube 52, and an additional pump is shown in outline at 
the corresponding position of the other conduit 32. The operation of this 
system is substantially the same as that previously described. It is 
convenient for the pump or pumps to have a manual or automatic device for 
reversing the direction of liquid flow periodically. (Similarly, a system 
using separate reservoirs could use detection of the level in a reservoir 
to actuate reversal.) 
FIG. 4 shows an automated dead end cleaning system. A gun 10 is held in a 
bracket 20 and coupled to an `input` conduit 32 and an `outlet` conduit 24 
much as in FIG. 1. The `outlet` conduit 24 passes to the waste reservoir 
26. But it includes a 3-way valve 60 from which a branch 62 leads to 
another 3-way valve 64 adjacent the input reservoir 34. The `input` 
conduit 32 is communicable with the input reservoir via a third 3-way 
valve 66 and the valve 64 adjacent that reservoir. The other branch 68 
from the third valve 66 leads to the waste reservoir 26. In one 
configuration of the valves 60,64,66, cleaning liquid from the input 
reservoir follows the arrows 70, into the gun via the `input` conduit 32 
and out via the `output` conduit 24. Possibly after a predetermined 
interval, the configuration of the valves is changed so that the cleaning 
liquid follows the path of the arrows 72, i.e. it enters the gun via the 
`output` conduit 24, and exits to the waste reservoir 26 via the `input` 
conduit 32. 
It may also be arranged for gas to be introduced into the fluid stream, to 
provide a more aggressive cleaning action, at least for the forward flow 
direction. Preferably compressed air for this purpose is introduced 
adjacent the inlet of the gun, e.g. via a junction 74 as indicated in FIG. 
1. 
It is preferred for the pump(s) to operate by compressed air, suitably 
being of peristaltic type, though of course other types of pump or motive 
power may be used. 
FIGS. 5 and 6 concern apparatus for cleaning suction- or gravity-feed guns. 
As shown, a suction-feed gun has a container 76 of liquid to be sprayed 
connected adjacent its spray outlet region 78. A supply of compressed air 
is fed in (through line 80) and emerges around the outlet of the liquid 
supply line in the outlet region 78 in a manner so as to create a low 
pressure region (by the Venturi effect), which draws liquid from the 
container 76. This liquid is then mixed with the compressed air, and 
discharged as a spray. (The gun can be similar in many respects to a 
pressure feed gun.) Once again, it is normal to employ an air cap which is 
retained by a retaining ring 82. As shown in FIG. 6 this can be employed 
to retain a coupling 84 which in many ways resembles the coupling 40 shown 
in FIG. 2. Thus it has the form of a tubular bushing, with an outer nozzle 
portion 86 to which a conduit may be connected for use in an array similar 
to that of FIG. 1. At the end where the coupling 84 is coupled to the gun, 
its internal bore widens to a stepped cylindrical chamber 88 which 
contains, at the inner end, a removable core 90. This core 90 has a 
central opening 92. The surface confronting the gun tapers towards this 
opening 92, e.g. being conical as shown. Peripheral portions 94 abut the 
gun substantially sealingly. Radially outwardly thereof, the main body of 
the coupling 84 also abuts, or is closely spaced from, the gun. Generally 
there is a small gap, and the body is firmly urged towards the gun by 
means of the retaining cap 82, so that the core 90 is forced against the 
gun. (There may also be a sealing ring at this location.) The core 90 is 
dimensioned so that it embraces the air outlet passages 96 of the gun; and 
so that the paint outlet nozzle 100 of the gun projects through and a 
short way beyond the aperture 92, there being an annular space between the 
nozzle and the wall of the core 90 that defines this aperture. Thus when 
compressed air is passed through its normal paths in the gun, it is 
funnelled through this annular passage and then enters the relatively 
large cylindrical chamber beyond. There is thus provided a suction effect 
which tends to draw material outwardly through the nozzle 100 of the gun, 
substantially as during normal spraying. 
FIG. 5 shows the coupling 84 passing directly into the inlet of a reservoir 
104. This reservoir has a simpler form than that shown in FIG. 1, having a 
single downwardly directed baffle 106. 
To clean a gun, it is merely necessary to remove the air cap, attach the 
coupling 84, put cleaning solvent in the paint container, and `spray` this 
solvent through the gun and into the coupling 84 (and thence into a 
suitable reservoir, e.g. as shown in FIG. 5 or FIG. 1). The construction 
of the coupling 84 in two parts, with the removal core 90, greatly 
facilitates the cleaning of the coupling. Furthermore, if the core is 
badly soiled or damaged, it can be cheaply replaced. Thus the narrow 
passage between the tip of the gun and the wall defining the aperture 92 
can be maintained with an efficient size and shape. Incidentally, many 
spray guns of this type, such as the JGV spray gun made by DeVilbiss and 
the BBR spray gun made by Binks Bullows, employ two series of compressed 
air passages. In addition to the main passages that open adjacent the tip 
of the gun, there are radially and forwardly displaced openings for 
spreader jets which serve to shape the spray of paint. These are 
separately controllable, and will generally be closed off during cleaning. 
(With a pressure feed gun, also the main air passages will be closed off 
during cleaning.) 
Interestingly, it has been found that when the air cap of a suction feed 
gun is replaced by a coupling 84, spraying of solvent under normal 
conditions (such as flow rate of compressed air) leads to a liquid flow 
rate substantially greater than the normal, spraying rate, for example 2.5 
times this rate. The reason for this increased rate is not yet clear, but 
of course it is most valuable since it enhances the cleaning effect and 
can thus reduce the time required for cleaning. 
FIGS. 7 to 9 show further examples of apparatus for use in cleaning 
pressure feed guns (though similar apparatus could be used for suction 
feed guns). FIG. 7 shows a gun 108 whose air cap has been removed. It is 
mounted in a cleaning housing by means of a bracket which provides a pair 
of support rods 110 like the rods 20 in FIG. 1. The housing has an end 
wall 112, and a coupling 114 is mounted at an opening 116 in that wall. 
The coupling 114 includes a tubular body 118 within which a tubular piston 
member 120 is axially displaceable, against the action of a spring 122 
which urges it into the interior of the cleaning housing. The piston 120 
has an inlet nozzle 124 which projects through an opening in the inner 
face of the body 118; and a shoulder portion 126 which is urged by the 
spring 122 to abut that face. The nozzle portion 124 is adapted to abut 
the outlet of the gun 108 in much the same way as the coupling 40 as shown 
in FIG. 2. Thus a sealing ring 128 is arranged to abut a frustoconical 
surface of the gun outlet, which outlet projects some way within an 
enlarged bore portion 130 of the nozzle portion 124. The coupling 114 is 
mounted relative to the bracket 110 such that, having regard to the 
dimensions of the guns with which it is to be used, the gun can be mounted 
in the bracket so that its outlet engages in the nozzle, sealing to the 
ring 128. Generally the piston 120 will be displaced rearwardly by the 
gun, so that it is urged into sealing contact with the gun's outlet by the 
spring 122. 
The coupling shown in FIG. 7 has three main parts. The body 118 comprises a 
cup member 132 (with an apertured base) and a closure plate 134. The third 
member is the piston 120 which is generally within the body, and which has 
a rear portion which extends slidably through an opening in the closure 
plate 134. The closure plate 134 may snap engage with the cup member 132, 
thus compressing the spring 122 between the plate 114 and the shoulder 126 
of the piston. FIG. 8 shows a simplified variant which has only two main 
portions: a tubular bushing 135 and a tubular piston 136. The bushing 135 
has a rear flange whose rear face abuts the wall 112 of the cleaning 
housing, and whose front face provides an abutment for a spring 138 which 
is braced against an enlarged head 140 at the inner end of the piston. 
This head provides a sealing abutment for the outlet of the gun 108. The 
piston 136 extends through the opening 116 in the wall 112 and bears a 
clip 141 to retain the assembly in place. 
Apparatus as shown in FIGS. 7 and 8 is very suitable for automatic 
operation, e.g. as shown schematically in FIG. 9. This shows a pressure 
feed gun 150 with a coupling 152 at its spray outlet. From the coupling 
152, a conduit 154 leads to a source and/or a collector for cleaning 
liquid. Adjacent the coupling 152 there is a junction for a compressed air 
inlet line 156. The paint inlet 158 of the gun is connected to a conduit 
160 leading to a source and/or collector for cleaning liquid. Adjacent the 
inlet 158 there is a junction for a compressed air line 162. 
The following automatic cleaning sequence may be carried out. Initially, 
cleaning liquid is passed through the gun via conduit 160 and the paint 
inlet, its cleaning effect being increased by the inclusion of compressed 
air passed through line 162. Dirty liquid from the gun passes along 
conduit 154 to a collector. After a predetermined interval, the inputs of 
liquid and air along conduits 160 and 162 are stopped, and conduit 160 is 
connected to a collector. The conduit 154 is connected to a source, and 
cleaning liquid is then backflushed through the gun, emerging through 
conduit 160. This backflush may also be enhanced by compressed air 
injection via line 156. Finally, there may be a compressed air purge. 
A number of preferred embodiments of the invention have been described, but 
the skilled reader will appreciate that much variation is possible. In 
particular, features described in connection with one embodiment may 
generally be combined with features described in connection with another. 
The invention can readily be applied to robot, automatic and 
semi-automatic spray guns; and to spray guns not only for spray painting 
but also as used for operations in other fields such a food technology 
(e.g. spray drying of milk), and ceramics. 
Whereas the invention has been described above by reference to preferred 
embodiments it will be understood by those skilled in the art that various 
changes may be made without departing from the spirit and scope of the 
invention, and it is intended to cover all such changes by the appended 
claims.