Manually controlled spraying installation and sprayer

An installation for spraying a coating product includes a manually controlled pneumatic sprayer operated by a trigger. The compressed air flowrate is varied according to the position of the trigger. The coating product feed system can include a gear pump driven at variable speed by a motor controlled by an electric signal representing the position of the trigger.

BACKGROUND OF THE INVENTION 
1. Technical Field of the Invention 
The invention concerns a manually controlled installation for spraying 
coating product, meaning an installation employing a manually controlled 
pneumatic sprayer including a trigger controlling both the flowrate of the 
coating product (paint) and the degree to which the valve controlling the 
input of air to spray this product is open. 
The invention is more particularly directed to improvements to secure 
better control of the flowrates of air and coating product. It finds a 
particularly advantageous application in installations employing 
two-component paints or varnishes (typically a base and a hardener) 
whereby the volumetric ratio between the two-components is better 
controlled under all circumstances. 
2. Description of the Prior Art 
A conventional manually controlled paint spraying installation comprises at 
least one pneumatic sprayer including a trigger and connected to a paint 
feed line and to a compressed air feed line. The paint is "atomized" and 
propelled by the air towards the object to be painted. The user controls 
the jet of sprayed paint by pressing the trigger to a greater or lesser 
extent. The paint passes through a valve controlled by the trigger. The 
valve exercises a proportional action, meaning that it is arranged in such 
a way that the flowrate of the valve is a function of the degree to which 
the trigger is depressed. The air feed control valve, also controlled by 
the trigger, is of the "on-off" type, however; this means that the air 
flowrate remains virtually constant whatever the paint flowrate. It has 
been found that this particular feature of known sprayers can in itself be 
prejudicial to good spraying. It can be deleterious to use too much air 
for a relatively low paint flowrate. It has been found that the excess air 
tends to dry the paint before it reaches the object to be painted, which 
can result in a bad finish. One object of the invention is to resolve this 
problem. 
SUMMARY OF THE INVENTION 
In one aspect, the invention consists in an installation for spraying a 
coating product, including at least one manually controlled pneumatic 
sprayer, a trigger on said at least one sprayer, means connected to said 
at least one sprayer to feed coating product to be sprayed thereto, a 
compressed air supply and means for progressively varying the flowrate of 
said compressed air responsive to the position of said trigger. 
The invention is further concerned with another improvement enabling the 
paint flowrate to be controlled more accurately, by using a gear pump in 
the paint feed circuit. The invention therefore also consists in an 
installation as defined above in which the coating product feed means 
include a gear pump, a motor adapted to drive said gear pump at variable 
speed, means for producing an electric signal representing the position of 
said trigger and control means for said motor responsive to said signal. 
The installation advantageously includes a sensor in said signal producing 
means responsive to the flowrate of said compressed air. 
Finally, it is particularly beneficial to apply the principles of the 
invention to the use of a two-component coating product in that a gear 
pump may be provided in each paint feed circuit and the pumps may be 
controlled so that their flowrates are maintained under all circumstances 
in a predetermined ratio corresponding to the optimum proportions of the 
two components. 
The invention therefore also consists in an installation as defined 
hereinabove adapted to spray a two-component coating product and including 
a mixer for said two components of said product on an input side of said 
at least one sprayer and having two inlets, one for each component, and an 
outlet connected to said at least one sprayer, a respective feed circuit 
for each component, a respective gear pump in each feed circuit on the 
input side of said mixer, respective motors adapted to drive said gear 
pumps at variable speed and respective control means for said motors 
adapted to maintain the flowrates of said two components in a 
predetermined ratio. 
In another aspect, the invention consists in a pneumatic sprayer adapted to 
be driven by compressed air, including a trigger and means for 
progressively varying the compressed air flowrate responsive to the 
position of said trigger. 
The invention will be better understood and other advantages of the 
invention will emerge more clearly from the following description given by 
way of non-limiting example only with reference to the appended 
diagrammatic drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With particular reference to FIG. 1, a manually operated paint sprayer 10 
includes in the conventional way a spray nozzle 11, a connector 12 
connected to a paint feed line 12a and a connector 14 connected to a 
compressed air feed line 14a. A trigger 16 is articulated at 17 to the 
body of the sprayer. It is coupled to the plunger of a proportional valve 
(not shown) controlling the paint flowrate. It is also coupled by an 
articulated rod 19 to means for progressively varying the flowrate of the 
compressed air. These comprise a flowrate adjuster valve 21 including an 
obturator member 22 movable relative to a seat 23 defined within a chamber 
24 between an inlet 25 connected to the connector 14 and an outlet 26 
connected to the spraying means. The rod 19 is attached to the obturator 
member 22 and a spring 28 in the chamber 24 urges the obturator member 
towards the seat 23, that is to say towards the closed position of the 
valve. 
The progressive adjustment of the air flowrate according to the position of 
the trigger is obtained by throttling the air over a variable axial 
distance in an annular passage 30 defined between the obturator member and 
the seat. To this end the obturator member comprises a core member 22a 
which is substantially cylindrical and the seat 23 comprises or is 
extended by a conduit portion 23a which is substantially cylindrical and 
the diameter of which is greater than that of the core member 22a. The 
variable length annular passage 30 is defined between the core member 22a 
and the conduit portion 23a. Acted on by the rod 19 and the spring 28, the 
core member moves axially within the conduit portion. The length d of the 
latter corresponds substantially to the travel of the trigger. 
Consequently, the head loss occasioned by throttling the air in the 
passage 30 and the resulting spraying air flowrate depend on the position 
of the trigger. The air flowrate and paint flowrate therefore vary 
according to the position of the trigger. In particular, for a low 
flowrate of paint there will be a low consumption of air, avoiding drying 
of the paint by the excess air. 
FIG. 2 shows in its simplest form an installation for spraying coating 
product using the sprayer from FIG. 1. However, this can be further 
simplified in that, as will be explained later, the paint flowrate control 
valve no longer needs to be of the proportional control type. In this 
installation the air feed means connected to the connector 14 include an 
air flowrate sensor 34 for measuring the spraying air flowrate as 
determined by the valve 21. This sensor, of any known type, is inserted 
between the compressed air supply, here represented by the line 36, and 
the sprayer 10. The sensor could of course be integrated into the sprayer. 
The sensor delivers at its output 34a an electrical signal representing 
the air flowrate and consequently the degree to which the trigger is 
depressed. The coating product feed means include a gear pump 38 driven at 
variable speed by a motor 39. The pump is inserted between a paint line 40 
and the connector 12. The motor 39 is energized by control means 42 (a 
current amplifier, for example) responsive to an electric signal 
representing the position of the trigger 16. This signal is produced at 
the electrical output 34a of the air flowrate sensor 34. 
In the alternative embodiment of FIG. 3 opto-electric means are used to 
produce the signal representing the position of the trigger 16. The latter 
is mechanically coupled to a pivoting reflective member 44 included in an 
optical fiber circuit 45, 46 established between a light source 47 and an 
opto-electric sensor 48. The latter is part of the means for producing the 
electric signal representing the position of the trigger. The electric 
signal output of the sensor 48 can therefore be connected to the control 
means 42 in the same way as the output 34a of the air flowrate sensor 34. 
The FIG. 2 embodiment is preferable because it has the additional advantage 
of rendering the pump also responsive to any fluctuations in the air 
pressure. In other words, in the event of malfunctioning of the air feed 
means, the paint flowrate can be modified automatically to maintain a 
substantially constant air-paint mix. This avoids the spraying of excess 
paint and therefore any risk of paint running. 
FIG. 4 shows a particularly beneficial application of the invention to the 
use of a two-component coating product, in particular a paint obtained by 
mixing a colored base and a hardener. The same sprayer as described above 
is used again. It is desirable to mix the components continuously, as the 
mixture is consumed. The installation therefore includes a mixer 50 on the 
input side of the sprayer 10. The mixer has two inlets 50a, 50b, one for 
each of the two components, and an outlet 51 connected to the connector 
12. The mixer is also connected via a check valve 52 to a cleaning unit 53 
known in itself including a solvent inlet 53a and a compressed air inlet 
53b. The installation comprises a paint (or base) feed circuit 55 and a 
hardener feed circuit 56. The outlet from the circuit 55 is connected to 
the inlet 50a of the mixer and the outlet of the circuit 56 is connected 
to inlet 50b of the mixer. The circuit 55 is connected to a color change 
unit 60 known in itself connected to several paint or base feed lines for 
different colors 61 -63, to an air feed line 65 and to a solvent feed line 
66. The circuit 55 therefore comprises in succession between the color 
change unit 60 and the mixer: a gear pump 67a driven at variable speed by 
an electric motor 68a, a flowrate sensor 69a and a purge valve 70a. A 
safety valve 71a is connected in parallel with the pump. The flowrate 
sensor 69a is advantageously of the "gear" type, meaning that its 
mechanical part is very similar structurally to a gear pump. One of the 
gears of this sensor is coupled to an inductive transducer 72a the 
electric output of which delivers a signal representing the liquid 
flowrate in the circuit 55. The hardener circuit 56 is in all respects 
comparable with the circuit 55. It is connected to a hardener line 78 and 
includes, interconnected in the same way, a gear pump 67b driven by a 
motor 68b, a flowrate sensor 69b with its transducer 72b, a safety valve 
71b and a purge valve 70b. 
The compressed air feed means are similar to those of FIG. 2 and therefore 
comprise an air flowrate sensor 73 connected between the line 65 and the 
connector 14. A computer 75 of any type, as available through normal 
commercial channels, for example, receives the output signals from the 
flowrate sensors 69a and 69b and from the air flowrate sensors 73 
(delivering a signal representing the position of the trigger) and 
delivers control signals to two current amplifiers 76a, 76b respectively 
feeding the motors 68a, 68b. The computer 75 forms part of the control 
means for the motors 68a, 68b. It is programmed to maintain the flowrates 
of the two components in the circuit 55 and 56 in a predetermined ratio. 
The system is set so that when the trigger is very slightly depressed a low 
flowrate of spraying air is established before paint is admitted into the 
sprayer. The plunger of the paint inlet valve is still closed at this 
time. The pump is enabled to operate only above a particular air flowrate 
for which it is certain that the valve plunger is effectively open. All 
these operating details can easily be processed by the computer 75. 
Likewise, on closing the valve, a minimum flowrate threshold is set prior 
to which the pump is stopped. The opening and closing thresholds may be 
different. It is also possible to stop the pump before closing the 
plunger, if the air flowrate sensor has a relatively slow response.