Flow, valve method

Automation is especially advantageous for analysing large numbers of samples on a routine basis. The flow injection method requires low sample volumes, hut even the recommended 600 pi loop size can be reduced to approximately 100 pi without substantial losses in sensitivity, accuracy or precision. In certain applications involving ICPs samples as small as 20 pi have been reported [7]. There is Httle doubt that sample introduction with a flow-injection valve and driven by a peristaltic pump or another... 

A similar PDMS valve control layer was used to achieve rotary liquid pumping for PCR [357]. In another report, a similar valving method was used to deliver cells and to introduce reagents for cell reactions. Solutions were pumped at 5-60 Hz to achieve a linear flow rate of 300-1000 pm/s [368]. 

Some valve manufacturers use the valve-flow coefficient C for valve sizing. This coefficient is defined as the flow rate, in gal/min, through a valve of given size when the pressure loss across the valve is 1 lb/in2. Tabulations such as Table 6.19 and flowcharts such as Fig. 6.9 incorporate this flow coefficient and are somewhat easier to use. Their accuracy equals that of the flow-coefficient method. 

Guidelines for sizing relief valves are given in API RP 520. Different design equations are recommended for vapor, liquid, steam, or two-phase flows. Sizing methods are also discussed in the DIERS Project Manual (Fisher et ah, 1992). 

For each parameter, the pH, DO (dissolved oxygen), ORP (oxidation-reduction potential), temperature, agitation speed, culture volume and pressure can be measured with sensors located in the fermenter. The output of the individual sensors is accepted by the computer for the on-line, continuous and real-time data analysis. Information stored in the computer control system then regulates the gas flow valves and the motors to the feed pumps. A model of a computer control system is shown in Fig. 11. The computer control systems, like the batch systems for mammalian cell culture, seem to level out at a maximum cell density of 10 cells/ml. It may be impossible for the batch culture method to solve the several limiting factors (Table 10) that set into high density culture where the levels are less than 10 cells/ml. 

I.Y. Kolotyrkina, L.K. Shpigun, Y.A. Zolotov, G.I. Tsysin, Shipboard flow injection method for the determination of manganese in sea-water using in-valve preconcentration and catalytic spectrophotometric detection, Analyst 116 (1991) 707. 

The remarks made in Section 8.1 translate across to the gas flow cases more or less word for word, except that the methods of Chapter 9 must now be allied to those of Chapter 6 in order to calculate gas flow through line and valve. But the more complicated equations for both line flow and valve flow render explicit solutions to the full set of equations impossible. Two implicit methods, the Velocity-Head Implicit Method (VHIM) and the Smoothed Velocity-Head Implicit Method (SVHIM), will be presented, where the solution process has been reduced to iteration on a single variable. The SVHIM is judged to be more accurate because it deals with the compressible-flow valve equations at all times. 

Gravity flow. This method is used wherever possible since it is safe it requires no expensive equipment and, by careful control of the outlet valve, the flow rate may be accurately controlled. Naturally, the basic requirement is that the outlet of the discharging vessel must be situated at a higher point than the receiving vessel (Fig. 2.6). 

The different methods of unloading may require different valve types and related equipment. In all cases, the liquid unloading lines should be equipped with pressure gauges and shut-off valves. As mentioned earlier, the unloading lines should be equipped with properly sized excess flow valves or emergency shut-off valves to protect against loss of product in the event of a hose failure. 

The ScienceFinder database was searched up to March 2014 for flow analysis methods for the determination of acesulfame-K, cyclamate, and saccharin. The keywords used as search criteria were flow injection analysis, sequential injection analysis, lab-on-valve, multicommutation, multisyringe, multipumping, as well as the individual sweetener names. As can be seen in Figure 24.2, only three flow analysis methodologies had been applied to the determination of these sweeteners, namely, flow injection analysis (FIA), sequential injection analysis (SIA), and multicommutation. 

The method is based on the international standard ISO 4053/IV. A small amount of the radioactive tracer is injected instantaneously into the flare gas flow through e.g. a valve, representing the only physical interference with the process. Radiation detectors are mounted outside the pipe and the variation of tracer concentration with time is recorded as the tracer moves with the gas stream and passes by the detectors. A control, supply and data registration unit including PC is used for on site data treatment... 

A separator is fed with a condensate/gas mixture. The condensate leaves the bottom of the separator, passes a flowmeter and is followed by a choke valve, after which the condensate is boiling. The flow can not be measured using the transit time method, due to the combination of short piping, the absence of a suitable injection point and the flow properties of the condensate, which is non-newtonian due to a high contents of wax particles The condensate can not be representatively sampled, as it boils upon depressuratioh... 

The most accurate flow rate control can be achieved by using the loss-in-weight method. The total amount of material required for a downstream process is first added to a tank or hopper scale. As the material is discharged, the loss-in-weight is monitored and used to modulate the discharge valve or gate to achieve the desired flow rate. 

Pinch The industrial equivalent of controlling flow bv pinching a soda straw is the pinch valve, Mves of this tvpe use fabric-reinforced elastomer sleeves that completely isolate the process fluid from the metal parts in the valve. The valve is actuated bv applying air pressure directly to the outside of the sleeve, causing it to contract or pinch. Another method is to pinch the sleeve with a linear actuator with a specially attached foot. Pinch valves are used extensively for corrosive material service and erosive sliirrv senice. This type of valve is used in applications with pressure drops up to 10 bar (145 psi),... 

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