Static-dynamic selection valve

Static/Dynamic Selection Valve. This valve is the key feature of our design in that it eliminates the use of a restrictor. Restrictors are the most common means of controlling the pressure or density of a supercritical process. With no restriction, flow is dead-ended (i.e. restricted) via a switching valve in our invention. Supercritical fluid extractions are then conducted in a static (no flow) mode. 

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. 

Figure 6. Static/Dynamic Selection Valve Setup for Six Vessel Multi-vessel Extractor. Extraction Effluent Received from One Tandem Column Switching Valve.

Figure 1 General setup used to carry out PFE. (A) Static mode and (B) dynamic and static-dynamic modes. WR, water reservoir HPP, high pressure pump SV, selection valve PH, preheater EC, extraction chamber C, cooler PV, pressure valve ER, extract reservoir INV, inlet valve RT, restrictor.

The selection of the pump cannot be separated from the design of the complete piping system. The total head required will be the sum of the dynamic head due to friction losses in the piping, fittings, valves and process equipment, and any static head due to differences in elevation. 

However, to date, it is generally agreed, by both researchers and practitioners that bottle testing is still a good guide (257). The bottle test is static and does not model closely the dynamic effects of water droplets dispersed or coalescing in the actual equipment such as control valves, pipes, inlet delivery, baffles, water wash, ete. If the point of injection of chemicals is upstream of the settler, then the test approximates the situation better. It is, however, still crucial that the characteristies of the emulsion be understood before the treatment system is selected (273, 274). 

---