Fluid dispensing system and valve control

Chemistry: analytical and immunological testing – Including sample preparation – Volumetric liquid transfer

Reexamination Certificate

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Details

C436S174000, C422S105000, C422S105000, C422S105000, C422S068100, C422S067000

Reexamination Certificate

active

06689621

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to a fluid dispensing system with a device for controlling the flow of fluids through a plurality of valves, and more particularly to a shaft-mounted cam that through a combination of translational and rotational motion can sequentially open or close one or more valves to precisely control the ratio of fluids added to a fluid mixture.
The use of valves and valve actuators to control the flow of gases and liquids in a fluid combining process or system is well known in the art. One area where precise actuation and control of the valves is critical is in chemical processes, where a large number of valves are employed, often in an extensive array of piping, conduit, ducting or related fluid carrying and containing equipment. The attendant level of monitoring and process control necessary to ensure that these larger, more complex valving systems are performing their intended tasks has rendered manual control of such systems difficult. In response, automated valve control was developed, and with the advent of computer-controlled systems, even more sophisticated ways to control and monitor any given chemical process have become commonplace. While the more precise, predictable control over valve closure and opening associated with automated devices has enabled improved system functionality, it has come with system cost, weight and complexity burdens.
Many of today's modern chemical processes, including oil or petroleum refining, food and drug manufacturing and electric generation, rely extensively on the complex interconnection of pumps, piping and valves to effect a particular chemical conversion or mixture. One of the more frequently used forms of chemical processing involves the use of a fluid dispensing system, wherein a single fluid transport conduit permits multiple fluids to be selectively injected into a main stream to create a final mixed product for dispensing. However, there are situations in which fluid dispensing systems, although potentially beneficial, have not found application. One example is the preparation of etchants for metals in the metallurgical laboratory. They are usually prepared in small quantities (typically 100 ml or less), and owing to their reactivity with metals are corrosive and hazardous by nature. Typically, these etchants are recipes comprising a mixture of constituents formulated to react with a given metal. As such, precise control over the ratios to ensure a quality etchant mixture is necessary. While such precise control with prior art systems embodying fluid dispensing features is possible, their reliance on multiple dedicated pumps or redundant valve and actuator engaging configurations results in complex, expensive systems that require that each actuator must be equipped with numerous dedicated devices in order to control multiple valves.
Another especially acute problem involves the precise control of minute quantities of fluids. When small quantities of injectants are being mixed, such as with medicament samples, acid etchants and related chemical reagents, the lack of a simplistic fluid dispensing system, which can meter precise amounts of the desired fluids reliably, affordably and safely is a hindrance to the creation of application-specific fluids. In response to ever-increasing demands that end product mixtures be of extremely high quality, with minimal contamination, waste and risk of exposure of personnel or the environment to hazardous substances, existing systems have added backup and redundant componentry, exacerbating system cost and complexity. Depending on the size of the fluid transport conduit in a fluid dispensing system, the driver fluid in the conduit's main stream could be either a conventional liquid (most notably water) carrier or an immiscible gas (most notably air) being drawn into the main stream through a supply valve. With a liquid-based driver system, a “pusher” fluid is used to move the injectant through the main stream of the conduit and into the dispensing unit. By using an “all liquid” approach (i.e.: liquid pusher and liquid injectant), the potential for an extremely accurate final mixture exists, due in part to the incompressibility of the liquids. However, the present inventors have discovered that the size of the conduit effects the mixing process. If the conduit is too large, the discrete volume of fluid in the conduit tended to collapse and mix with the pusher fluid. Likewise, if the size of the conduit is too small (as can be the case when small quantities of injectant are used), friction effects can dominate, resulting in slow dispensing speeds and higher power requirements.
In metallurgical laboratories, metallurgists and metallurgical technicians routinely prepare etchants, mixtures of acids, solvents, and salts, which are used to etch metallographic samples, thus revealing microstructure and other features. The preparation of etchants, as it is currently practiced in the metallurgical lab, entails: the transfer of acids and solvents from the bottles in which they are supplied to smaller containers to facilitate handling; the measurement of volumetric quantities of these acids and solvents using graduated cylinders; and the mixing of the same in a container along with mass quantities of salts, if required. The handling and measurement activities are time consuming and entail significant risk to both personnel and the environment. Alternatively, some laboratories transfer acids and solvents from the containers in which they were purchased into an individual dispenser for each reagent, or insert a bottle top dispenser into each bottle in which a reagent is purchased. After the etching operation is completed, the etchant must be neutralized prior to disposal. Many laboratories perform the pH neutralization procedure with sodium hydroxide pellets. Because sodium hydroxide is highly reactive in acid, as are related acid neutralizers, it must be added slowly to minimize foaming and spatter. Personnel performing this operation check the neutralization process frequently using litmus paper to determine the pH of the solution. This can be tedious, time-consuming, and potentially dangerous to personnel, adjacent laboratory equipment and the ambient environment. In addition, it is frequently the case that too much neutralizer is added, thus necessitating the addition of more acid in an ad hoc process to ensure that an acceptable pH (typically in the range of 6 to 8) is reached prior to disposal. Not only does the prolonged exposure due to this back-and-forth process present additional risks to personnel, equipment and the environment, but it generates additional quantities of waste product as well.
Other applications for a fluid dispensing system capable of handling acids and solvents exist outside of the metallurgical laboratory. One example is compositional analysis of metals in the chemical laboratory using a technique known as inductively coupled plasma. Prior to analysis, the metal to be analyzed must be placed in liquid solution. To accomplish this, chemists dissolve the metallic sample in mixtures of acids and solvents similar to etchants. In the chemical laboratory, the preparation, neutralization and disposal of these solutions of acids and solvents proceeds in much the same way as it does in the metallurgical laboratory. Similarly, in other contexts, examples of commercially available systems exist in which a peristaltic pump is devoted to each liquid to be dispensed. Such systems may be combined with valve manifolds to redirect liquids to a plurality of locations. Valves in such manifolds are generally activated individually using electromechanical devices such as solenoids. Other commercially available systems use multiple screw driven syringes or multiple syringe pumps to dispense a multiplicity of liquids. In any event, exposure to harsh chemicals can present safety and operability risks that typically require additional costs associated with redundant, protective system componentry.
Accordingly, there exists a need for

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