Fluid delivery systems syringe pumps

Briefly the positions of the valve are used in a manner illustrated in Figure 3. Position 1 is fitted to a 1/16" stainless steel tee (T3) fitting for delivery of fluid from the system syringe pump to the two 6-port tandem selectors for 12 column operation. In the 6 column system, this tee is eliminated. If six column operation is desired on the twelve column system, an on/off valve placed in line with one of the exit tubes (OU-4) from the stainless steel tee is manually closed and single delivery to one tandem selector is achieved. Position 2 of the VALCO selector valve delivers modifier from the liquid pump to each one of the extraction vessels automatically. 

Once the extraction is complete, the static/dynamic selection valve is repositioned to the dynamic mode to allow flow. Subsequently, pressure and density are rapidly reduced to prevent significant losses of the supercritical fluid from the syringe pump tank and the extraction effluent, which is being transferred for collection. With a non-re-stricted transfer, the flow of supercritical fluid effluent is rapid. This desire for rapid depressurization led to the development of a delivery nozzle which would ensure collection of the extracted solutes without losses. Details of this delivery system can be found in the next section. 

Most flow-based analytical procedures rely on constant flow rates (Fig. 3.4a). These have also been used in model systems designed for studying sample dispersion, in order to simplify the related mathematical models. Uniform solution delivery is accomplished by exploiting pumping devices relying on pistons such as automatic burettes or syringe pumps, peristaltic pumps with dampeners, or gravity as fluid propellers. 

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