Patent Publication Number: US-8986074-B2

Title: Fluid control circuit for wet abrasive blasting

Description:
FIELD OF THE INVENTION 
     The invention is directed to a fluid control circuit. An embodiment of the fluid control circuit is for wet abrasive blasting systems used for cleaning, preparing surfaces, removing coatings, and/or other abrasive blasting operations. Embodiments of the fluid control circuit provide the ability and enable a user, among other things, to more easily obtain a consistent slurry flow which results in a more efficient blasting operation as compared to conventional wet blasting systems. Embodiments of the invention provides an accurate, simple, and intuitive control of the fluid supply system, which is used to pressurize the blast pot, control the metering of the wet abrasive, and/or allow for pressure washing (without media). In certain embodiments of the fluid control circuit, all these operations may be controlled through one selector valve. 
     BACKGROUND 
     To remove the paint, dirt or other surface coating from a substrate such as a surface to be painted or cleaned, a blasting system is desirable and effective. There are a variety of blasting processes for these purposes, including, but not limited to, water blasting, dry abrasive blasting, and wet abrasive blasting. In certain applications, abrasive blasting systems are able to efficiently clean or remove a coating without damaging the underlying metal or other substrate, although in other applications, a certain degree of surface roughening may be desired. 
     The use of dry abrasive blasting with particles, such as those used in conventional sand blasting, may result in excessive surface roughness and other damage to the substrate. Typical blast particles are hard and abrasive in order to increase the efficiency of the blasting operation but may, therefore, result in damage to the substrate. Soft recyclable blast particles are sometimes substituted to avoid surface damage. These recyclable blast particles include, but are not limited to, agricultural products such as crushed walnut shells, crushed pistachio shells, corn husks, and rice hulls. Plastic particles are sometimes used to reduce substrate surface damage but may also result in a reduction in efficiency of the blasting operation. 
     Wet abrasive systems have been used to also control and reduce surface damage. Wet abrasive systems combine the benefits of water blasting systems with dry abrasive blasting systems. In wet abrasive blasting, the fluid can encapsulate particles of the abrasive media to simultaneously add mass to the abrasive and buffer the impact of the abrasive against the substrate to reduce potential surface damage, but still effectively strip or clean the surface while also reducing the dust produced by dry blasting. However, wet abrasive systems require efficient mixing of the slurry with a gas stream to produce a consistent blast stream comprising a three-phase mixture of fluid, solid abrasive, and gas. If the mixing of slurry and pressurized gas is not well controlled, the blasting process is less efficient and, therefore, the benefits of the wet abrasive system are not fully realized. 
     There is a need for a wet abrasive system that is easier to control in order for the benefits of a wet abrasive system to be more fully realized. In the past, the control has been overly complicated and required extensive training before an operator became fully proficient. Even then, there remained the possibility of operator error because multiple selector valves have at least nine different positions which could be selected (only one being the correct position); therefore, there were eight possible erroneous positions for any one function. 
     SUMMARY 
     Wet abrasive systems comprise a combination of equipment, controls, and piping systems that allow the fluid flow to be controlled in order to provide the various operations desired to be performed to remove the paint, dirt or other surface coatings from a substrate, such as a surface to be painted or cleaned. A fluid control circuit includes piping systems for directing the fluid to different locations or equipment of the wet abrasive blasting system for the various operations. For example, a fluid control circuit is configured to provide control over the fluid flow for the various operations of a wet abrasive blasting system. The fluid control circuit allows a user to switch from one operation to the next depending on the stage of the abrasive blasting operation including, but not limited to, filling the blast pot, blasting the substrate with a three phase flow of solid blasting media, a fluid, and compressed gas, rinsing the substrate with the fluid, blowing down or drying the substrate with compressed gas, and rinsing the equipment and general work area. 
     An embodiment of the fluid control circuit comprises a multiport selector valve comprising a fluid inlet, and at least two fluid outlets including a first fluid outlet and a second fluid outlet. The selector valve allows selective fluid communication between the fluid inlet and either the first fluid outlet or the second fluid outlet. A first piping system is in fluid communication with the first fluid outlet and a second piping system is in fluid communication with the second fluid outlet to direct the fluid flow to different locations in the wet abrasive blasting system. In one embodiment, the fluid control circuit comprises a jumper piping system between the first piping system and the second piping system. The jumper piping system may comprise a check valve, wherein the check valve allows flow from the first piping system to the second piping system but prevents flow from the second piping system to the first piping system. 
     In a specific embodiment, the first piping system provides fluid communication between the first fluid outlet and the bottom of a blast pot and the second piping system provides fluid communication between the second fluid outlet and the top of the blast pot. 
     In another embodiment, the fluid control circuit for a wet abrasive blasting system may comprise a third fluid outlet in fluid communication with a third piping system in fluid communication with a rinse hose and nozzle. 
     An embodiment of the wet abrasive blasting system comprising a blast pot, the blast pot comprising a top inlet and a bottom inlet, a fluid control circuit, the fluid control circuit comprising a multiport selector valve comprising a fluid inlet, a first fluid outlet, and a second fluid outlet, a source of pressurized fluid in fluid communication with the fluid inlet, a first piping system in fluid communication with the first fluid outlet and the bottom inlet, a second piping system in fluid communication with the second fluid outlet and the top inlet, and jumper piping system between the first piping system and the second piping system, the jumper piping system comprising a check valve. The check valve may allow flow from the first piping system to the second piping system but prevents low from the second piping system to the first piping system. 
     The terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting of the invention. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well as the singular forms, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one having ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     In describing the invention, it will be understood that a number of components, parts, techniques and steps are disclosed. Each of these has individual benefit and each can also be used in conjunction with one or more, or in some cases, all of the other disclosed techniques. Accordingly, for the sake of clarity, this description will refrain from repeating every possible combination of the individual steps in an unnecessary fashion. Nevertheless, the specification and claims should be read with the understanding that such combinations are entirely within the scope of the invention and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a general schematic drawing of a wet abrasive blasting system; 
         FIG. 2  is a schematic drawing of a prior art fluid control circuit of a wet abrasive blasting system; 
         FIG. 3  is a schematic of an embodiment of a fluid control circuit of a wet abrasive blasting system; 
         FIG. 4  is a schematic of an embodiment of a fluid control circuit of a wet abrasive blasting system illustrating the fluid flow in Fill/Flush mode to fill and pressurize the pot; 
         FIG. 5  is a schematic of an embodiment of a fluid control circuit of a wet abrasive blasting system illustrating the fluid flow in Blast mode; 
         FIG. 6  is a schematic of an embodiment of a fluid control circuit of a wet abrasive blasting system illustrating the fluid flow in Wash Down mode; 
         FIG. 7  is a schematic of an embodiment of a fluid control circuit of a wet abrasive blasting system illustrating the fluid flow in Rinse/Off mode; 
         FIG. 8  is a schematic of an embodiment of a fluid control circuit of a wet abrasive blasting system illustrating the fluid flow in Wash Down Mode to Flush Abrasive from Internal Plumbing; and 
         FIG. 9  is a schematic of an embodiment of a fluid control circuit of a wet abrasive blasting system illustrating the fluid flow in Fill/Flush Mode to Expel Media from Pot. 
     
    
    
     DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Embodiments of the fluid control system comprise a unique piping system that allow simple and effective control of the fluid supply system for the various operations of a wet abrasive blasting system. 
     Wet abrasive systems comprise a combination of equipment, controls, and piping systems that allow the fluid flow to be controlled in order to provide various operations desired to be performed to remove the paint, dirt or other surface coatings from a substrate such as a surface to be painted or cleaned. A fluid control circuit includes piping systems for directing the fluid to different locations or equipment of the wet abrasive blasting system for the various operations. For example, a fluid control circuit is configured to provide control over the fluid flow for the various operations of a wet abrasive blasting system. The fluid control circuit allows a user to switch from one operation to another depending on the desired operation of the abrasive blasting including, but not limited to, filling the blast pot, blasting the substrate with a three phase flow of solid blasting media, a fluid, and compressed gas, rinsing the substrate with the fluid, blowing down or drying the substrate with compressed gas, and rinsing the equipment and general work area. 
     An embodiment of the fluid control circuit comprises a multiport selector valve comprising a fluid inlet, and at least two fluid outlets including a first fluid outlet and a second fluid outlet. The selector valve allows selective fluid communication between the fluid inlet and either the first fluid outlet or the second fluid outlet. A first piping system is in fluid communication with the first fluid outlet and the bottom of the blast pot and a second piping system in fluid communication with the second fluid outlet and the top of the blast pot. In one embodiment, the fluid control circuit comprises a jumper piping system between the first ping system and the second piping system, wherein the jumper piping system comprises a check valve, wherein the check valve allows flow from the first piping system to the second piping system but prevents flow from the second piping system to the first piping system. This system allows fluid flow to be directed to both the top and bottom of the blast pot when the selector valve is positioned for fluid communication with the first fluid outlet for filling and flushing but only directs fluid flow to the top of the blast pot with the selector valve is positioned for fluid communication with the second fluid outlet for blasting. In a specific embodiment of the fluid control system, the second piping system comprises a flow control or metering valve. In one such embodiment, the jumper piping connects to the second piping system downstream of the metering valve as shown in  FIG. 3 . 
     In another embodiment, the fluid control circuit for a wet abrasive blasting system may comprise a rinse outlet in fluid communication with a rinse piping system in fluid communication with a rinse hose and nozzle. 
     As such, an embodiment of the wet abrasive blasting system comprising a blast pot, the blast pot comprising a top inlet and a bottom inlet, a fluid control circuit, the fluid control circuit comprising a multiport selector valve comprising a fluid inlet, a first fluid outlet, and a second fluid outlet, a source of pressurized fluid in fluid communication with the fluid inlet, a first piping system in fluid communication with the first fluid outlet and the bottom pot inlet, a second piping system in fluid communication with the second fluid outlet and the top pot inlet, and a jumper piping system between the first piping system and the second piping system, the jumper piping system comprising a check valve. The check valve may allow flow from the first piping system to the second piping system but prevents flow from the second piping system to the first piping system. 
     A further embodiment of the fluid control circuit comprises a multiport selector valve comprising a fluid inlet, and at least two fluid outlets including a first fluid outlet and a second fluid outlet. The selector valve allows selective fluid communication between the fluid inlet and one of the first fluid outlet and the second fluid outlet. A first piping system is in fluid communication with the first fluid outlet and a second piping system in fluid communication with the second fluid outlet to direct the fluid flow to different locations in the wet abrasive blasting system. In one embodiment, the fluid control circuit comprises a jumper piping system between the first piping system and the second piping system. The jumper piping system may comprise a check valve, wherein the check valve allows flow from the first piping system to the second piping system but prevents flow from the second piping system to the first piping system. 
     In another embodiment, the fluid control circuit for a wet abrasive blasting system may comprise rinse fluid outlet in fluid communication with rinse piping system in fluid communication with a rinse hose and nozzle. 
     An embodiment of the wet abrasive blasting system comprising a blast pot, the blast pot comprising a top inlet and a bottom inlet, a fluid control circuit, the fluid control circuit comprising a multiport selector valve comprising a fluid inlet, a first fluid outlet, and a second fluid outlet, a source of pressurized fluid in fluid communication with the fluid inlet, a first piping system in fluid communication with the first fluid outlet and the bottom pot inlet, a second piping system in fluid communication with the second fluid outlet and the top pot inlet, and jumper piping system between the first piping system and the second piping system, the jumper piping system comprising a check valve. The check valve may allow flow from the first piping system to the second piping system but prevents flow from the second piping system to the first piping system. 
     In one embodiment, a fluid control circuit for a wet abrasive blasting system comprises piping systems including four check valves (one check valve in jumper piping between a first piping system and a second piping system, one check valve prior to the inlet at the top of the blast pot, one check valve prior to the inlet at the bottom of the blast pot and one in the wash down piping system), one quick coupler, two ball valves, and one precision metering valve, all of which are in fluid communication with a four-way selector valve. This unique combination produces the capability to perform at least eight different operations of a wet abrasive blasting system. The eight functions include fill, flush, expel media from abrasive hose, expel media from the internal plumbing, blast, power wash, rinse, and air dry. In this embodiment, the eight functions may be controlled by positioning the single selector valve to one of only four positions (and is some cases, opening/closing another valve or coupling/uncoupling piping), this substantially reducing the possibility of operator-error. The fluid piping systems and fluid control circuit allows for greater control and consistency of the mixing of the gas and slurry, resulting in a more consistent flow of the three-phase blasting stream and a more efficient wet blasting process. 
     As used herein, “pipe” and “piping” shall mean any fluid containment device used to convey liquid or gas, such as a tube, hose, duct, pipe, or other similar structure. The pipe may have any cross-sectional shape, including rectangular, square, circular, or other shape. The flow area of the pipe is defined by its internal cross-sectional area. 
     As used herein, “piping system” shall mean pipe, and other components used to connect one part of a system to another. The other components may include, but are not limited to, valves, check valves, elbows, tees, reducers, regulators, connectors, gauges or gauge connectors, flow or temperature sensors, pressure gauges, and control valves. 
     As used herein, “fluid” or “fluids” are liquids. Preferably the fluids are substantially incompressible fluids, such as water. 
     Typically as shown in  FIG. 1 , the flurry piping system  15  connects a blast pot  11  comprising the slurry to a slurry/gas mixer. In certain embodiments of the wet abrasive blasting system, the blast pot  11  contains a mixture of a solid particulate and a fluid (hereinafter “slurry”), and the fluid being under pressure in the blast pot  11  causes the slurry to be conveyed through the slurry piping system  15  at a desired flow rate from the blast pot  11  to the mixer  20 . The pressurized gas piping system  21  is connected to a source of pressurized gas in order that the gas may be conveyed through the pressurized gas piping system  21  to the slurry/gas mixer  20  and is capable of conveying the desired flow rate of pressurized gas to the mixer  20 . The three-phase blasting system exits the mixer  20  in the blast hose  26  to the blast nozzle  27 . 
     Typically, the gas will be air and the fluid will be water, but other gases and fluids may be used. In addition, additives may be combined with the fluid or the gas, as desired, such as, but not limited to, to prevent flash rusting or to keep the liquid from freezing. The fluid is mixed with an abrasive media in the blast pot to form the slurry. 
     The abrasive media of the slurry may be any desired non-floating particulate matter capable of being transferred as slurry through the system. For example, the abrasive media may include media in the range of United States Standard Sieve Screen Size 100μ˜10μ. The media and fluid are mixed into the blast pot, the ratio is variable as long as the slurry may be pushed through the slurry piping system fairly evenly and consistently. The cone shape of the bottom of the vessel and the fact that the media is heavier than the fluid causes the slurry to funnel into a hose or pipe that connects the blast pot to the input piping of the mixer. 
     The slurry piping system  15  and/or the pressurized gas piping system  21  may comprise pipe and other components as defined above. The size of the piping system depends on the size and capacity of the wet abrasive blasting system. Larger piping is needed to make the greater flow rate of larger systems. 
     An embodiment of a wet abrasive system  10  is depicted in  FIG. 1 . This embodiment comprises a blast pot  11 . The blast pot  11  comprises a conical bottom  12  with a slurry exit  19  positioned at the lower end of the conical bottom  12 . Such a blast pot  11  is advantageous for use with solid particulate or media that is heavier than the fluid, typically water, and which will not significantly rust or absorb a significant amount of the fluid, to be used in the blasting operation. Media such as sponge, untreated baking soda, crushed walnut shells, ground corn cob, and plastics have densities less than water and will float and/or absorb water. Such media may be used in a blast pot with an exit at the top of the blast pot, such as a conical top, for example. Blast pots of other configurations may also be used in the wet abrasive blasting systems, such as pots with flat or elliptical bottoms, or pots with tops or bottoms of other desired shapes. 
     The blast pot may further be comprised of a bung (pop-up), valve, flanged top, or other sealing mechanism that allows the blast pot to be purged of gas and pressurized by a source of pressurized fluid, such as a pump  14  or other source of pressurized fluid. Thus, the system may also include a blast pot similar to conventional dry-blasting, however, unlike conventional dry-blasting, the vessel is pressurized by a fluid, such as water, and there is substantially now air in the vessel during the blasting operation. Air trapped in the blast pot may result in pressure fluctuations because air is compressible, while water is substantially incompressible. The pump  14  shown in  FIG. 1  is an air-operated pump. An air-operated pump may be convenient for use in wet abrasive systems as it may be operated from the same compressed air used to connect to the pressurized gas piping. However, the fluid pump may be powered by any source, such as electricity, for example. The media and fluid are mixed into the blast pot and the slurry ratio is determined by the size and weight of the individual particle. The desired slurry ratio depends on the blasting operation to be performed and the material of the substrate to be cleaned or stripped, as well as other factors such as the composition of the coating being removed. The cone-shaped bottom of the blast pot and the fact that the media is typically heavier than water causes the slurry to funnel into a hose or pipe that connects the blast pot to the input piping of the control panel. In this manner, the slurry may be pumped or pushed into the mixer to be combined with the pressurized air to form the abrasive spray. The abrasive spray is a combination of solid and liquid (from the slurry) and gas (from the pressurized gas source). 
     The wet abrasive blasting system  10  of  FIG. 1  further comprises a slurry piping system  15  connecting the blasting pot  11  to the mixer  20 . The slurry piping system  15  comprises pipe  16  and other components, including elbows  19  (in this embodiment both 90-degree elbows and 45-degree elbows are used), a manual shut-off valve  17 , and an air operated shut-off valve  18 . In one embodiment, the components have a similar internal flow area and thus are capable of supplying a consistent slurry pressure to the mixer during operation without resulting in significant cavitation or other pressure fluctuations. Other embodiments of the slurry piping system of the wet abrasive blasting system may or may not include these components and/or may include other components. 
     The wet abrasive blasting system  10  of  FIG. 1  further comprises a pressurized gas piping system  21 . In this embodiment, the pressurized gas piping system  21  comprises a compressed air connector  22  capable of connecting the gas piping system  21  to a source of pressurized gas such as, but not limited to, an air compressor or a pressurized tank, for example. The pressurized gas system  21  further comprises pipe  23 , a pressure regulator  24 , and a check valve  25 . Other embodiments of the pressurized gas system of the wet abrasive system may or may not include these components and may or may not include other components. 
     A check valve in the air supply piping system provides back-flow protection to prevent slurry entering into the gas piping system. A check valve in any of the piping systems may be, but is not limited to, a flapper check valve, a weighted check valve, or a spring-loaded check valve, for example. Preferably, in certain embodiments, the check valve may have a cracking force of approximately 2 psi or a cracking force of greater than 2 psi. Further, to mitigate the risk of slurry entering the check valve and preventing the valve from closing and/or to assist slurry from being cleared from the check valve, the check valve may further be installed in a vertical position with the flow of the pressurized air in a downward direction. Further, the check valve may be installed in a position above the mixer. In contrast, in some conventional wet abrasive piping systems, the check valve is installed in a horizontal position. The horizontal position can contribute to filling and blocking the gas piping system with slurry. 
     To properly mix with the pressurized air, the slurry may be forced into the control panel or mixer at a force substantially equal to or greater than the force of the compressed air (the back pressure) as it passes through the slurry piping system and across the connection point of the slurry&#39;s piping into the mixer with the compressed air on its way to and through the blast hose  26  and the blast nozzle  27 . 
     To create a consistent flow of slurry, the blast pot typically may be maintained at a pressure in the range from approximately 40 psi to approximately 140 psi or greater. A fluid pump is used to fully fill the blast pot with fluid, which already contains media. A venting process then removes substantially all of the air. Once the air is expelled, a sealing valve or bung is used to seal the blast pot, which is not substantially free of compressible gas. As the fluid pump continues to pump, fluid pressure will develop in the blast pot. The pump flow maintains the pressure in the blast pot and during operation forces the slurry into the mixer via the slurry piping system. The slurry piping system may be comprised of a manually operated ball valve, which allows the pressure in the vessel to be isolated from the control panel during the fill process. The ball valve is also used for clean-out purposes (providing the ability to safely reuse the media), and for wash-down purposes, which may be some of the added features to a working wet abrasive blasting system. 
     The driving force of the slurry through the spray nozzle of the wet abrasive blast system may be provided by a high-volume (40˜900 CFM, for example) air compressor attached to the pressurized piping system. The pressure at which the compressed air is delivered to the mixer may be controlled by an air regulator designed to handle the volume of air being supplied by the compressor. 
     As previously discussed, the regulated air may be plumbed through a vertical check-valve with a cracking force of approximately 2 psi. The check valve is designed to be in the vertical position and, in some embodiments, positioned at least two inches above the height of where the slurry and air are mixed. Such an arrangement effectively blocks feed-back of slurry from getting into the air regulator and air control circuitry. 
     An air-controlled or electrically controlled shut-off valve may also be incorporated in the slurry piping system so the operator has the ability to simultaneously turn off the pressurized air supply and shut-off the slurry valve by means of a “dead man” switch at the blast nozzle or from a remote location. This action prevents slurry from being forced up into the pressurized air piping system (while not blasting) due to the fluid pressure&#39;s force in the blast pot. 
     In operation, the compressed air “powers through” the slurry being forced into the air/slurry stream. It is this action that causes the slurry to be “picked up” and propelled through the piping, the blast hose, and the nozzle. The mixture of compressed air, fluid, and media is accelerated by the action of the nozzle and becomes the working blast force used for cleaning, stripping, and removing unwanted coatings, linings, or rust. 
     Propulsion is effectively enhanced due to the fluid mixed with the media (slurry). The fluid serves to encapsulate the media which then aids the compressed air in the transport of the media and also serves as a dust suppressant when the media is blasted out of the nozzle and onto the substrate. The fluid mixed with the media (slurry) also serves the purpose of “lubricating” the interior of the blast hose so that the media can travel more efficiently in a “stream” rather than travelling dry through the blast hose, as is done in dry blasting systems. 
     In one embodiment, the wet abrasive blasting system comprises a vertical check valve located more than two inches above the entry height of the slurry into the blast stream. This design takes advantage of gravity and space to help reduce the possibility of slurry back-feeding into the pressurized air piping system. Although other wet-blast systems exist, the majority of these systems inject water at the nozzle, thus losing many of the effective features of this design. One primary example being the fact that the slurry is easier to transport through the blast hose (the liquid acting as a lubricant) with less drag, thus keeping the speed of each particle higher than in a dry system or a system that injects water at the nozzle. The higher speed of each particle results in a higher momentum factor for the wet abrasive blast design as compared with a dry system that injects water at the final stage at the nozzle. Testing has proven that the identical blast hose and nozzle combination lasts up to 5 times longer in a wet-abrasive blast system as compared with a dry system, thus supporting the lubrication factor. 
     As described earlier, the pressurized blast pot (pressure maintained by a fluid pump in a system from which substantially all of the air has been vented) is just one component in the wet abrasive blasting system, the purpose of which is to create positive flow of slurry through the mixer and into the air stream. Obviously, once the air-controlled slurry shut-off valve is opened, the pressure in the pot and the pressure in the airstream will attempt to equalize. Typically, a higher pressure in the blast pot than the pressure in the air stream is due to the resistance of the slurry and the setting of the fluid pump, which provides consistent positive flow of slurry to the mixer. In certain embodiments, the fluid pump&#39;s pressure output regulator may be set at least 15˜20 psi higher than the intended blast pressure. Testing has shown that as long as the pressure in the blast pot is maintained at or above the blast pressure, the slurry is forced into the air stream rather than air being forced backwards toward the blast pot. The pressure in the blast pot (once initially set) may be maintained by an adjustable flow-control valve (metering valve). The setting of this valve predictably controls the volume of slurry being forced into the air stream. As this valve injects fluid into the pot (using pressurized fluid from the fluid pump), the same amount of slurry is forced into the air stream based on the principle that the fluid in the pot cannot be compressed and, therefore, additional fluid forced into the pot must equal the same volume of slurry forced out of the pot. 
     A fluid control circuit diverts flow of fluid to various locations in the wet abrasive blasting system to perform various operations. In a specific embodiment, the fluid control circuit needs to provide at least eight functions in order to accomplish an easy, yet efficient wet abrasive blasting system. The eight functions may be:
         1. Fill and Pressurize the blast pot with fluid (“Fill”);   2. Maintain Pressure in the pot during blasting operation (“Blast”);   3. Wash down (“Wash Down”) blasted substrate through blast nozzle without abrasive in the mixture (after blasting);   4. Blow down (“Blow Down”) of blasted substrate with compressed gas;   5. Rinse (“Rinse”) with use of rinse hose;   6. Dilute clogged abrasive in abrasive hose from pot to mixer (“Flush”);   7. Flush internal plumbing (“Fill/Flush” with abrasive hose ball valve closed and quick coupler disconnected);   8. Final flush to expel any unspent media from the internal plumbing and the blast pot (“Fill/Flush” with abrasive hose ball valve open).       

     The prior art system&#39;s fluid control circuit, used on conventional wet abrasive blasting systems, is shown in  FIG. 2 . The prior art system comprises two, three-way valves or selector valves. Each three-way ball valve or selector valve has an inlet connected to the source of pressurized fluid such as, in the embodiment shown in  FIG. 2 , a fluid supply pump  14 . The fluid supply pump  14  is in fluid communication with the first selector valve  31  by fluid piping  100  and with the second selector valve  32  by fluid piping  100  and  101 . Each selector valves  31  and  32  has three positions creating fluid communication with the three outlets of the selector. The first selector valve comprises outlet A in fluid communication with the bottom of the blast pot outlet B which is blocked, and outlet C in fluid communication with the slurry piping between the manual ball valve and the diaphragm valve (both not shown in  FIG. 2 , but shown in  FIG. 1 ). The second selector valve  32  comprises outlet D in fluid communication through a metering valve or flow control valve  33  with the top of the blast pot outlet E which is blocked and outlet F in fluid communication with the top of the blast pot beyond the metering valve. 
     The first piping system  102  may be considered to be in fluid communication with the bottom of the blast pot  11  if the first piping system  102  is connected to the slurry piping system  15  at the bottom of the blast pot  11  or other location wherein fluid may flow to the conical bottom  12  of the blast pot  11 . To perform the Fill and Pressurize step (No. 1) on a conventional wet abrasive blast unit, the first selector valve should be set to B, and the second selector valve should be set to F so that the fluid flow goes directly to the top of the pot without going through the metering valve. 
     To perform the Blast step (No. 2) on the conventional wet abrasive blast unit, the first selector valve should be set on B and the second selector valve set on D so the fluid flow to the top of the blast pot may be controlled with the metering valve. 
     To perform the Wash Down step (No. 3) on the conventional wet abrasive blast unit, the abrasive hose ball valve  17  (shown in  FIG. 1 ) must be closed, the first selector valve  31  should be set on C and the second selector valve  32  set on E so the fluid flows directly into the slurry line between the abrasive hose ball valve  17  and the diaphragm valve  18  (shown in  FIG. 1 ) to be propelled by the compressed gas through the blast hose and nozzle as a fluid/gas mixture, without any abrasive. 
     To perform the Blow Down step (No. 4) on the conventional wet abrasive blast unit, the first selector valve should be set on B and the second selector valve set on E, and the abrasive ball valve  17  (illustrated in  FIG. 1 ) closed, so that the fluid and abrasive flow is stopped, leaving only gas propelled through the blast hose and nozzle. 
     To perform the Rinse step (No. 5) on the conventional wet abrasive blast unit, the first selector valve should be set on B and the second selector valve set on E and the Rinse valve  36  set to open. This provides fluid at the full volume of the fluid pump to aid in clean up or to help wash the media into the pot during initial setup. 
     To perform the Dilute clogged abrasive step (No. 6) on the conventional wet abrasive blast unit, the first selector valve should be set on A and the second selector valve set on E and the metering valve  35  opened fully to allow fluid to be injected into the abrasive hose at the bottom of the pot. This serves to dilute any clogging of the media that may occur if the unit sits idle for too long of a period. 
     To perform the Flush Internal Plumbing step (No. 7) on the conventional wet abrasive blast unit, the abrasive hose ball valve  17  (illustrated in  FIG. 1 ) should be closed so that the abrasive hose&#39;s quick coupler can be disconnected safely. The first selector is set on C and the second selector is set on E. This will cause media inside the internal plumbing (below the diaphragm valve) to be flushed out of the opened quick coupler. 
     To perform the Final Flush step (No. 8) on the conventional wet abrasive blast unit, the first selector valve should be set on A and the metering valve  35  should be fully opened. The second selector valve set on F so the fluid flows directly to the top of the blast pot. With the abrasive ball valve closed, the quick coupler can be safely opened. The disconnected abrasive hose can now be flushed clean by opening the abrasive hose ball valve. 
     The complexity of the steps and ability to set the selector valves in positions that do not perform a particular function demonstrates the problems with the design and configuration of the conventional fluid control circuits and fluid piping of conventional wet blasting systems. These problems result in possible operator error due to all of the possible combinations of positions presented by two or more selector valves and metering valves. The selection of each process is complicated by having to set each selector valve in the correct position and if the selector valves are not turned in the correct position the desired operation may not be accomplished or accomplished inefficiently. As previously stated, both the first selector valve and the second selector valve are connected to the source of pressurized fluid through a common piece of piping. During a Blast operation, the user could incorrectly set the first selector valve to A and the second selector valve to D simultaneously. This directs fluid through the “Abrasive Metering valve” to the top of the blast pot and also through the “Water Metering valve” to the bottom of the blast pot. The blasting may appear to be operating normally, but additional fluid is being added at the bottom of the blast pot, diluting the slurry. This produces an inefficient blasting operation that is, unfortunately, difficult to notice, especially for inexperienced operators. 
     The fluid control system described herein as new technology eliminates this combination possibility. The inventor determined that many users were setting the prior art blast equipment to this combination of A and D (some intentionally) and flooding the blast (media to fluid ratio), thus using too much media and consuming too much fluid and causing “run-off”—a major issue in some states, especially California. Depending on the proximity to storm drains or natural water ways, this could also become a pollution issue. 
     In the same manner, the user could mistakenly select C and F simultaneously setting the selector valves to Fill and Wash Down at the same time while intending to be in Blast mode. This would totally bypass both metering valves and result in a very inefficient and uncontrolled wet abrasive blasting system. The water control system and selector valve positioning of conventional wet abrasive systems are not intuitive and can prove to be difficult to set correctly for inexperienced operators. 
     Often the two major mistakes users perform, described above, result in inefficient wet abrasive blasting operations, and the benefits of the wet abrasive system are defeated. The inventor devised an easier to use and operate system, which greatly reduces the opportunity for operator error. This innovation allows an inexperienced operator such as, for example, a person merely renting a system with little training in wet abrasive blasting, to operate the machine almost as effectively as an experienced operator. 
     For example, the inventor realized that for conventional wet blasting systems, service calls are generally due to operator error in setting up the fluid configuration system, and not due to problems with the wet abrasive blasting system. These problems are not because there are failures of components in the wet abrasive blasting system. Typically they are due to operator confusion concerning the correct combination of positions or settings of two or more selector valves and two or more metering valves utilized on conventional, prior art wet abrasive blasting systems. 
     For example, at certain times (i.e. after a prolonged idle period on a very hot day), the slurry flow may be diminished or completely stopped, resulting in only air exiting the blast hose. Should such a situation exist, this invention has added an additional function to the fluid control system called the “Flush” function. This function can be activated by simply turning the selector valve to the indicated position (without the need for any other adjustment, such as changing the setting of a metering valve). Returning the selector to the “Blast” position, after the situation has been resolved, results with reduced possibility of an operator error because no other adjustment or setting needed to be changed and the metering valve remains how it was previously set. This is not the case in conventional prior art wet blasting systems. 
     Embodiments of the fluid control circuit for the wet abrasive blasting system described herein provide a smooth, consistent, predictable, and controlled flow of slurry and produce far less chance of operator error than conventional wet abrasive systems. Thus, the wet abrasive blasting system is safer and more efficient to use (both for the operator and the environment). 
     An embodiment of the fluid control system is shown in  FIG. 3 . The fluid control system has one selector valve  33 . In this embodiment, the selector valve  33  is a four way valve comprising one inlet G for the source of pressurized fluid and four fluid outlets (H, I, J, K). In the embodiment shown in  FIG. 3 , only one of the outlets H, I, J, and K may be selected at any time. The four outlets are as follows: 
     1. Outlet H (first fluid outlet) is used in the Fill/Flush step and is in fluid communication with both the top inlet of the blast pot and the bottom inlet of the blast pot. Specifically, this is done through first piping system  102  to the bottom of the blast pot and through jumper piping  107  by opening check valve  36  and second piping system  106  to the top of the blast pot. The blast pot is filled from the top and bottom inlets in this mode, preventing dry media from clogging the abrasive hose at the bottom of the pot. 
     2. Outlet I (second fluid outlet) is used in the Blast step and is in fluid communication with the top of the blast pot through the second piping system  106  and the metering valve  37 . As discussed previously, efficient operation of the wet abrasive blasting process is performed when the fluid enters at the top of the blast pot and exits through the bottom nozzle with the entrained abrasive. In the embodiment of the wet abrasive blasting system shown in  FIG. 3 , fluid will not flow through the jumper piping  107  with the selector valve  33  in communication with outlet I (second fluid outlet) because the check valve  36  will remain closed. The jumper piping system  107  comprises a check valve  36  that allows fluid flow from first piping system  102  to second piping system  107  and jumper piping system  106  so that outlet H is in fluid communication with both the top and the bottom of the blast pot  11 , however, check valve  36  does not allow flow from piping system  106  to piping system  102 , therefore, outlet I is not in fluid communication with the bottom of the blast pot but is only in fluid communication with the top of the blast pot  11  through the metering valve  37 . 
     The four way valve (selector valve  33  in  FIG. 3 ), jumper piping  107  and check valve  36  eliminate the need for the second selector valve of the prior art conventional system of  FIG. 2 . An embodiment of a fluid control system for a wet abrasive blasting system comprises a selector valve  33  with a first fluid outlet H in fluid communication with a first piping system  102  to the bottom of a blast pot  11 , a second fluid outlet I in fluid communication with a second piping system  106  to the top of a blast pot  11 , and jumper piping system  107  between the first piping system  102  and the second piping system  106 . In a particular embodiment, the jumper piping system  107  comprises a check valve  36  that prevents fluid flow from the second piping system  106  to the first piping system  102  but allows fluid flow from the first piping system  102  to the second piping system  106 . 
     3. Outlet J is connected to a bypass piping system  108  to bypass the blast pot  11  and direct fluid into the top of the slurry piping system, without abrasive, and then into the blast hose  26  and nozzle  27  providing a pressurized wash down feature. 
     4. Outlet K is in fluid communication with a rinse piping system including a rinse ball valve  109  and rinse hose (not shown). The rinse piping system  109  bypasses the wet abrasive blasting system to aid in loading the media into the blast pot  11  and to allow general cleanup of the equipment and the blasting area. 
     As previously mentioned, the blast pot should be substantially purged of the air from within to reduce an accumulator effect caused by compression and expansion of trapped air. In one embodiment of the wet abrasive blast system, the air from the blast pot is vented during filling of the blast pot with fluid through an automatic air-purging vent. The air may be substantially vented during the fill step with the selector set on the “Fill/Flush” function of the selector valve. A schematic of an embodiment of the fluid control circuit of a wet abrasive blast system in Fill/Flush mode is shown in  FIG. 4 . The piping systems in fluid communication with the fluid inlet of selector valve  33  an the air supply piping are shown in bolt. A ball valve  17 , installed between the outlet  28  of the blast pot  11  and the inlet of the mixing tee  20 , is closed to prevent flow of slurry to the mixing tee  20  during this operation. 
     The blast pot  11  is filled and pressurized by the fluid pump&#39;s flow being directed through the selector valve inlet G in fluid communication with outlet H. The fluid flows to the Lower Pot Check Valve  39  and also to the Upper Pot Check Valve  40  through the jumper piping system  107  by opening the Fluid Circuit Check Valve  36 . This action pressurizes the blast pot  11  in preparation for blasting. 
     When the selector valve  33  is turned to the “Blast” function and the abrasive ball valve  17  is opened, the fluid pump&#39;s flow is directed through the selector valve inlet G to outlet I and through the metering valve  37  and through the Upper Pot Check Valve  40  to maintain pressure and, when desired, flow to the top of the blast pot for blasting. The fluid cannot open the Fluid Circuit Check Valve  36  to flow into the blast pot&#39;s lower check valve  39  due to the orientation of the Fluid Circuit Check valve  36 . This provides metered control over the volume of wet abrasive that will be forced into the air stream because the existing volume of media and fluid in the blast pot  11  cannot be compressed. Therefore, any additional fluid forced into the top of the blast pot  11  must result in the same volume of wet media being forced out of the bottom of the blast pot  11 . A schematic of an embodiment of the fluid control circuit of a wet abrasive blast system in Blast mode is shown in  FIG. 5 . The piping systems in fluid communication with the fluid inlet of selector valve  33  and the air supply piping are shown in bold. 
     After blasting has been performed, it may be desirable to pressure-wash the blasted surface. This can be accomplished with the abrasive ball valve  37  closed and turning the selector valve to outlet J for “Wash Down” mode. In this position, the fluid pump&#39;s flow is directed through the selector valve G to outlet J and then through the Wash Down Check Valve  41 . This forces fluid, without additional abrasive, into the piping that carries slurry during blasting. The fluid, without abrasive media, is fixed into the compressed air stream and serves as a power wash through the blast hose. A schematic of an embodiment of the fluid control circuit of a wet abrasive blast system in Wash Down mode is shown in  FIG. 6 . The piping systems in fluid communication with the fluid inlet of selector valve  33  and the air supply piping are shown in bold. 
     After washing down the blasted surface it may be desirable to blow down the surface with air to aid in drying the surface. This is accomplished by turning the selector valve  33  into the “Rinse/Off” mode. In this mode, the fluid pump&#39;s flow is directed through the selector valve G to outlet K but then it is blocked because the rinse ball valve is closed. The slurry is also blocked by the abrasive hose ball valve  17  in the off position. This will allow only compressed air to pass through the blast hose. A schematic of an embodiment of the fluid control circuit of a wet abrasive blast system in Rinse/Off mode is shown in  FIG. 7 . The piping systems in fluid communication with the fluid inlet of selector valve  33  and the air supply piping are shown in bold. 
     Using the “Rinse/Off” function, it may be desirable to have access to the water pump&#39;s flow for washing off the machinery or aiding in washing the media into the blast pot during initial setup. The fluid pump&#39;s flow, through the selector valve inlet G to outlet K, is controlled by opening the rinse ball valve  38  to allow fluid to flow through a rinse hose attached to the rinse piping system  109 . 
     As mentioned earlier, in certain circumstances, such as using ultra-fine abrasives (smaller than 120 grit) or when the equipment has been sitting idle for long periods of time (especially in hot weather), the abrasive flow through the abrasive hose  120  to the mixer  20  could become too slow or stopped. In such a circumstance, the “Fill/Flush” function will cause the fluid pump&#39;s flow to be directed through the selector valve inlet G to outlet H and then through the Fluid Circuit Check Valve  36  and then through the blast pot&#39;s top check valve  40  and bottom check valve  39 , thereby introducing fluid, at the initial pot pressure setting, to dilute the clogged abrasive and allow the abrasive media to begin flowing again. When the clog has been cleared the fluid control circuit is set back to Blast Mode. 
     Finally, at the end of the shift or job, it may be prudent to expel all of the unspent media from the certain piping and from the blast pot  11 . This is accomplished by first turning the abrasive ball valve  17  into the closed position, so one can safely uncouple the Quick Coupler  42 . A catch bucket may be positioned under the open piping and the selector valve  33  set to the Wash Down position allowing the fluid pump&#39;s flow to be directed through the selector valve inlet G to outlet J and then through the wash down check valve  41 . This will wash all of the media, still inside the slurry piping system  106 , out through the open quick coupler  42 . A schematic of an embodiment of the fluid control circuit of a wet abrasive blast system in Flush Piping mode, to expel media from the piping and hose, is shown in  FIG. 8 . The piping systems in fluid communication with the fluid inlet of selector valve  33  and the air supply piping are shown in bold. 
     By turning the selector valve  33  to the “Fill/Flush” position, the fluid pump&#39;s flow will be directed through the selector valve inlet G to outlet H and then through the Fluid Circuit Check Valve  36  and through the pot&#39;s top check valve  40  and the bottom check valve  39 . This will introduce fluid, at the initial pot pressure setting, which will push down like a piston on the media inside the pot and which will also be injected into the clean-out tee at the bottom of the pot. This in turn will dilute the media in the abrasive hose  120  and cause it to flow out through the open quick coupler  42  (controlled by the abrasive hose ball valve  17 ). A schematic of an embodiment of the fluid control circuit of a wet abrasive blast system in Final Flush mode to expel media from the blast pot  11  is shown in  FIG. 9 . The piping systems in fluid communication with the fluid inlet of selector valve  33  and the air supply piping are shown in bold. 
     The embodiments of the described fluid control circuits and wet abrasive blasting systems are not limited to the particular embodiments, components, method steps, and materials disclosed herein as such components, process steps, and materials may vary. Moreover, the terminology employed herein is used for the purpose of describing exemplary embodiments only and the terminology is not intended to be limiting since the scope of the various embodiments of the present invention will be limited only by the appended claims and equivalents thereof. 
     Therefore, while embodiments of the invention are described with reference to exemplary embodiments, those skilled in the art will understand that variations and modifications can be effected within the scope of the invention as defined in the appended claims. Accordingly, the scope of the various embodiments of the present invention should not be limited to the above discussed embodiments, and should only be defined by the following claims and all equivalents.