Solvent and air mixing system

The solvent and air mixing system is used in an air solvent purging/cleaning system for an at least two liquid component mixing and applying system or a paint color changing system. The mixing and applying system includes at least two sources of liquid coupled to a mixer through respective control valves. An air solvent purging/cleaning system is provided including an air supply line and an air purge valve and a solvent supply line and a solvent purge valve coupled to the mixing and applying system or to a paint color changing system. A pneumatic valve control system is provided for controlling the supply of pressurized air to the air purge valve and for controlling the supply of solvent to the solvent purge valve. The solvent and air mixing system of the present invention includes a solvent and air mixing device having an air passageway coupled into the supply line for supplying pressurized air to the air purge valve. A solvent valve is coupled to the solvent supply line and to the solvent and air mixing device and communicates with a transverse passageway that opens onto, and is in communication with, the air passageway in the solvent and air mixing device. Control structures are coupled to the solvent valve for controlling operation of the solvent valve and for controlling the amount of solvent delivered from the solvent valve through the transverse passageway to the air passageway in the solvent and air mixing device. Preferably, part of the control structure is the pneumatic valve control system.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a liquid delivery line purging or cleaning 
system where at least two lines are brought to a mixer for combining or 
mixing of the liquids and subsequent application of the combined/mixed 
liquids. One line is purged or cleaned with solvent and the other line 
with air. The method and system of the present invention add a small 
amount of solvent to the air in the air cleaning line which is used to 
purge or clean the other line. 
2. Description of the Related Art Including Information Disclosed Under 37 
CFR .sctn..sctn.1.97-1.99 
Heretofore, in paint spray systems, where it is necessary to change the 
paint color available to the spray operator, a device called a color 
changer is employed. A color changer is a stack of valves, each valve 
supplied by an independent paint source such as a pump in a large 
container of a particular type of color of paint. Each valve supplies 
paint to a manifold common to all valves. By opening one valve of a 
particular color, the manifold then directs that paint to a conduit (hose) 
that supplies the paint applicator or application device, typically a 
paint spray gun, sometimes handheld, sometimes robotic, etc. 
The type of applicator is irrelevant to the present invention. The purpose 
of the applicator is to start and stop the delivery of the paint and to 
atomize or otherwise dispense it. In applications where rapid changes from 
one color to another are necessary, color changers are employed. 
This is the sequence of events during a color change using color changers: 
1. The spray applicator is closed to stop fluid (paint) flow. 
2. The spray applicator is positioned to direct the waste paint into a 
waste container. 
3. The "opened" color valve is closed. 
4. The spray applicator is activated to relieve fluid pressure from the 
color changer through the paint supply hose and through an outlet from the 
spray applicator. 
5. An air color change valve (Air Purge Valve) on the color changer is 
opened, introducing compressed air to the color changer and paint hose to 
expel the waste paint through the hose and into the waste container. 
Regardless of the paint supply pressure, this air pressure typically is 
the maximum air supply pressure available in the plant, or typically never 
above approximately 120 psi. It is not unusual for this air supply 
pressure to be as low as 90 psi. 
6. Once the compressed air evacuates the paint hose, the air purge valve is 
closed and a solvent color change valve (Solvent Purge Valve) is opened. 
The purpose of the solvent is to wash away any old paint that still clings 
to the walls of the color changer manifold, hoses, and spray applicator. 
Solvent pressure is typically set to be at the same pressure as the paint 
pressures that supply the paint valves. There are typically three groups 
of paint supply pressures, depending on the spray applicator used in the 
paint process: 
A. Airspray--50 to 120 psi 
B. Air Assisted Airless--700 to 1200 psi 
C. Airless--1200 to 3000 psi 
There are many variations of these categories depending on paint viscosity, 
etc., and a wide range of paint pressures relative to the air pressure are 
available to the air purge valve. 
7. From this point, the solvent and air purge valves alternately open and 
close to provide an alternating solvent and air scrub that is more 
effective in a cleaning action than by solvent itself. The cycle may 
continue until the operator stops it, or it may be automatically 
controlled by a computer or other electro-mechanical device. When the 
operator does not open or vent the spray applicator, problems can occur. 
If the spray applicator is not opened before the color change process 
begins, or if the spray applicator is closed during the purge process, the 
purge process will accomplish nothing since the waste does not have 
anywhere to go. 
The air purge valve will open to blow the paint hose out with 100 (plus or 
minus) psi. The paint hose, ballooned up from the paint pressure, and, 
given that the spray applicator is not activated to release this pressure, 
the old paint will move backwards through the air purge valve and into the 
compressed air supply lines. When the air pressure and the decreased fluid 
pressure balance, the backwards flow of paint will stop, and will then 
move forward again when the operator activates the spray applicator. This 
error is minimized by the use of check valves on all paint valves on the 
color changer, as well as on the solvent and air purge valves. There is, 
however, a small cavity in the air purge valve, between the valve seat and 
the face of the check valve. This cavity in the air purge valve holds 
compressed air which will be further compressed by the introduction into 
this cavity of the higher pressure paint when the air purge valve opens. 
The problem becomes more and more severe as paint pressures get higher. In 
fully automatic paint systems, such as robotic, where the spray gun 
trigger can be activated automatically prior to the color change 
sequencing, this is usually not an issue, though the robot has no way of 
knowing if the spray applicator dispensing tip is plugged, at which time 
there could still be a backflow issue because the pressurized paint has 
nowhere to go but backwards. 
Once the air purge valve needle and seat are contaminated by paint, the air 
purge valve is subject to leaking. It will be a matter of time before the 
check valve becomes contaminated too. Any time after that, the compressed 
air supply may be subject to the same failure mode as described above. 
Note that the compressed air passing through the air purge valve and 
associated check valve does a poor job of cleaning, and is not intended to 
do any real cleaning at all, but only is intended to push old paint out of 
the way so that the cleaning solvent can do its job. 
In addition, there are two component paints that, until both components are 
blended together (catalyzed), the components remain generally fluid. Once 
mixing is initiated, however, those paints will turn into a hard material 
over time. The only way to stop this hardening is to break down the 
material by flushing with solvent. Should this catalyzed material 
contaminate the air purge valve, it is a fact that the valve needle and 
seat will leak causing catalyzed paint to move into the compressed air 
supply. 
It is possible to use solvent in all lines, "solvent only", to clean the 
paint passages, thereby eliminating the compressed air altogether. Some 
paint or liquid mixing systems actually do this. The chief disadvantage to 
doing this is that the solvent usage necessary to clean the system 
increases greatly, in volume, to accomplish the same level of cleaning as 
when using compressed air along with the solvent. However, due to solvent 
cost, waste solvent disposal costs, and Environmental Protection Agency 
limits on hazardous waste generation such as waste disposal and solvent 
emissions, this is not the desirable option. 
The layout of the valving in some two component mixing systems is such that 
the solvent purge valve is located to clean the catalyst passageways, and 
the air purge valve is located to clean the resin passageways. Solvent and 
air come together in the same cavity that the resin and catalyst come 
together to mix. The reason that the solvent is installed on the catalyst 
side of the mixing system is that the catalyst is subject to degradation 
when exposed to air, or more specifically, the moisture (water, humidity) 
present in air. The catalyst side is, therefore, protected by the presence 
of solvent. In order to effect the most efficient cleaning procedure, the 
air, therefore, is introduced on the resin side. Protected by check 
valves, this layout is no different in operation than the paint color 
changing system described above. 
Eventually the air purge valve needle and seat will become contaminated, be 
subject to leaking, and eventually be subject to allowing mixed paint 
and/or solvents to move backwards through the compressed air supply 
system. 
SUMMARY OF THE INVENTION 
According to the present invention there is provided a solvent and air 
mixing system for use in an air solvent purging/cleaning system for an at 
least two liquid component mixing and applying system or a paint color 
changing system. The mixing and applying system includes at least two 
sources of liquid coupled through respective control valves to a mixer. 
The air solvent purging/cleaning system includes an air supply line and an 
air purge valve and a solvent supply line and a solvent purge valve which 
are coupled to the mixing and applying system or to a paint color changing 
system. Structure is provided for supplying pressurized air to the air 
purge valve. Structure also is provided for supplying solvent to the 
solvent purge valve. A pneumatic control system is provided for 
controlling the operation of the air purge valve and the solvent purge 
valve. The solvent and air mixing system of the present invention includes 
a solvent and air mixing device having an air passageway coupled into the 
supply line for supplying pressurized air to the air purge valve. The 
solvent and air mixing system also includes a solvent line coupled to the 
solvent supply structure and a solvent valve connected to the solvent 
line, an outlet of the solvent valve being coupled to the solvent and air 
mixing device and communicating with a transverse passageway in the device 
that opens onto the air passageway in the solvent and air mixing device 
and that communicates with the air passageway. Control structures are 
associated with the solvent valve for controlling operation of the solvent 
valve and for controlling the amount of solvent delivered from the solvent 
valve through the transverse passageway to the air passageway in the 
solvent and air mixing device.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
Referring now to the drawings in greater detail, there is illustrated in 
FIG. 1 a solvent and air mixing system 10 constructed according to the 
teachings of the present invention. This system 10 is shown in conjunction 
with a two component mixing system 12 used to mix two liquid components. 
It will be understood that instead of a two component mixing system 12, 
the solvent and air mixing system 10 can be utilized with a paint color 
changing system (not shown). 
As shown in FIG. 1, in the two component mixing system 12, a catalyst 
source 14 supplies catalyst through a meter 16 to a catalyst delivery 
valve 18 where delivery of catalyst through a delivery line 19 to a mixer 
20 is controlled. 
At the same time, resin from a resin source 24 is supplied through a meter 
26 to a resin delivery valve 28 that controls the flow of resin through a 
delivery line 29 to the mixer 20. 
The output from the mixer 20 is delivered to an applicator (not shown) such 
as a spray gun or robotic liquid delivery system. 
Catalyst and resin mixing systems 12 on two or more paint mixing systems 
and paint color changing systems are typically of the type sold by Binks 
Manufacturing Company, DeVilbiss, Inc. or Graco, Inc. 
During the use of the two component mixing system 12, the mixed liquid is 
delivered to an applicator such as a spray gun. 
When it is time to clean or purge the lines, tubings, hoses and valves, 
e.g., lines 19 and 29, and valves 18 and 28 of the mixing system 12, an 
air solvent purge system 30 controlled by a pneumatic valve control system 
31 is actuated to supply pressurized air to an air purge valve 32 of the 
system 30 to open same and to a solvent purge valve 34 of the system 30 to 
open same. 
First, however, the catalyst delivery valve 18 and the resin delivery valve 
28 are closed. Next, the operator opens the applicator, such as by 
squeezing a trigger of a spray gun. Then, the pneumatic valve control 
system 31 is operated to supply pressurized air, first to the air purge 
valve 32 for opening same to supply purging air to the resin lines, e.g. 
line 29, mixer 20 and outlet hose/applicator, with compressed air. Next, 
pressurized air is supplied by the control system 31 to the solvent purge 
valve 34 to open the solvent purge valve 34 to supply solvent to the 
catalyst lines, e.g., line 19, and to the mixer 20 and outlet 
hose/applicator. 
According to the teachings of the present invention, a solvent and air 
mixing device 40 of the solvent and air mixing system 10 is provided and 
connected into a compressed air purge supply line 42 of the air solvent 
purge system 30 leading to the air purge valve 32, as shown. Further, a T 
connector 44 is connected into a pressurized air control line 46 from the 
pneumatic valve control system 31 for the air purge valve 32, as shown. A 
tubing or hose 48 from the T connector 44 is coupled to a solvent valve 50 
mounted to the solvent and air mixing device 40. In this way, the same 
control pressure used to open the air purge valve 32 also opens the 
solvent valve 50. 
The solvent valve 50 can be a conventional valve of the type normally used 
with the two component mixing system 12 or with a paint color mixing 
system. 
As shown in FIG. 1, a T-connector 51 is provided in a solvent supply line 
52 that supplies solvent to the solvent purge valve 34. A tubing or hose 
53 extends from the T-connector 51 to the solvent valve 50 as shown. 
As best shown in FIG. 3, an outlet 54 from the solvent valve 50 
communicates through a filter 55 with a transverse passageway 56 in the 
solvent and air mixing device 40 that opens, at 58, onto an air through 
passageway 60 in the block shaped device 40 connected into the air purge 
supply line 42. 
A solvent throttling member 62, in the form of a screw-in member 62 with an 
orifice 64 therethrough is provided in the transverse passageway 56. The 
screw-in member 62 is shown in larger detail in FIG. 4. Typically, the 
throttling passage 64 has a diameter of 0.040 inch, but can be a different 
size dependent upon orifice size needed to achieve a desired solvent to 
air ratio. 
The filter 55 can be made of any known material and one material that 
provides satisfactory results is an expanded solvent resistant plastic 
mesh material. As shown in FIG. 3, the transverse passageway 56 is 
countersunk at 66 to provide a recess 66 for receiving the filter 55. 
The filter 55 protects the orifice 64 from clogging with debris in the 
solvent supply. 
In the use of the solvent and air mixing device 40, only a small amount of 
solvent is added to the pressurized air for the purpose of wetting areas 
in the resin delivery system or paint delivery system which may become 
contaminated with resin, catalyst or paint. 
The solvent can be alcohol, water, MIBK, MEK, MAK, xylol, toluol, butyl 
cellosolve or other suitable solvent for cleaning paint lines and valves. 
The ratio of air to solvent is between 50:1 to 150:1 by volume. 
Also, it is to be understood that the solvent air mixing system 10 of the 
present invention is integrated into an existing air solvent purge system 
30 controlled pneumatically by the pneumatic valve control system 31. 
The solvent and air mixing device 40 is designed to mix solvent into the 
compressed air stream that supplies the air purge valve 32. The solvent is 
supplied to the solvent and air mixing device 40 at the same supply 
pressure as is used on the solvent supplied to the solvent purge valve 34. 
This solvent pressure should be set at the highest paint pressure supplied 
to the mixing chamber in the mixer 20, or slightly higher (+20 PSI), to 
assure that there can be no backwards movement of the fluid column. The 
solvent valve 50 on the solvent and air mixing device 40 opens and closes 
simultaneously with the opening and closing of the air purge valve 32. 
Should the spray applicator not be opened to allow the paint hose to 
depressurize when the purge cycle is initiated, solvent will be dispensed 
by the solvent valve 50 of the solvent and air mixing device 40 into the 
air purge line, 42 and 60, to bring the air passage up to the solvent 
pressure which, if the system 30 is set up properly, will balance the 
paint pressure with the air/solvent pressures in the air passageways, 
preventing backflow of paint through the compressed air system, line 42. 
A check valve on the air inlet to the solvent and air mixing device 40 
closes when the pressure in the air passageway 60 becomes higher, due to 
solvent introduction, than the applied air pressure. There is nothing else 
that can be done, if the operator does not trigger the spray applicator, 
than to add some solvent to the air passage to dilute any mixed paint that 
did move backwards. The solvent and air mixing system 10 does this 
automatically. As the solvent and air/paint column moves forward during 
the first portion of the purge cycle, the solvent and air mixing device 40 
returns automatically to its metering function that allows a large 
percentage of air as opposed to solvent, to flow, and allows the air to 
resume its scrubbing action. 
The benefits of the solvent and air mixing device 40 in the solvent and air 
mixing system 12 are as follows: 
1. Provides controlled volume of solvent in an air purge stream to clean 
fluid passages in paint, ink, or other fluid handling devices that were 
previously cleaned by air only. 
2. Enhances the cleaning of paint systems where a solvent/air chop is used 
during a purge cycle. 
3. Works automatically with the air purge valve and needs no additional 
external controls. 
4. No variable orifice exists that can be manipulated or closed by 
unauthorized personnel to cancel proper function. The screw-in member 62 
with the fixed orifice 64 is replaceable and optional orifice sizes can be 
chosen to control maximum solvent amounts dispensed into the air stream. 
The filter 54 protects the orifice 66 from clogging. 
5. The solvent valve 50 on the solvent and air mixing device 40 provides a 
positive stop to prevent unintentional dispensing of solvent into the 
mixed material stream. Solvent pressure is not applied at all times to the 
air purge valve. 
6. Provides additional check valve in the system 30 to assure no material 
backflow. 
7. Provides automatic pressure compensation in the air purge supply line, 
for a fluid column that may be at a higher pressure than the compressed 
air column. 
8. In two component paint systems (regardless of paint pressures) that have 
color changers on the resin (A) side, along with a gear meter to measure 
the resin flow, it was previously impossible to use air in the purge cycle 
because air pushing through the meter would burn up the gears and meter 
housing. (Meters cost $3,500.00 to $4,000.00). It would greatly enhance 
the speed and efficiency of the purge cycle if air could be used in the 
resin (A) color changer. In this application, the solvent and air mixing 
device 40 would be set to supply enough solvent to cool the gears, and 
thus allow for use of a solvent/air chop into the color change cycle. 
From the foregoing description, it will be apparent that the solvent and 
air mixing system 10 including the solvent and air mixing device 40 and 
the solvent valve 50 of the present invention has a number of advantages, 
some of which have been described above and others of which are inherent 
in the invention. Also it will be understood that modifications can be 
made to the solvent and air mixing system 10 described above without 
departing from the teachings of the present invention. Accordingly, the 
scope of the invention is only to be limited as necessitated by the 
accompanying claims.