By-pass loop

Small lengths of piping (approx. 1 m in length) can be fitted to plant using appropriate flanges and can provide valuable data as to plant corrosion characteristics. The spool can only be removed at shut-down. An alternative procedure is to install the spool on a by-pass loop. 

The valves need to isolate a pump and provide emergency manual control on a by-pass loop. 

Originally, it was believed that an external by-pass of higher hydrodynamic resistance than that of the sample cavity was needed to avoid pressure build-up during the manual switching of the valve between the sampling and inject positions. It was found, however, that the internal short by-pass loop L2 in Fig. 5.1 is sufficient provided that the switching of the valve is executed rapidly. 

Figure 5.3. Six-port valve integrated into a FIA microconduit. The valve is turned by the lever, proper matching of the ports in the two positions being secured by the two stops fixed on the baseplate. The valve is shown in the sampling position where sample solution (5) is being aspirated into the sample loop (5L) and from here to waste (W). In this position the reagent carrier stream (R) is shunted by the small by-pass loop to the manifold and detector (D). For further details, see text [5.1].

By using these fairly clean, dry and hot gases, we were able to build a simple heat exchanger with standard components. The gases, with an average temperature of 230°C, are taken out after the gravel bed filter into a by-pass loop. By controlhng the speed of the fans the water temperature is held at a desired... 

Without an autosampler, an interface can be constructed from an eight-port, two-position sample valve with sample and by-pass loops of appropriate volumes, an injection device that delivers aliquots of the column effluent isolated in the sample loop into the graphite furnace, and electronic control and switching circuitry that allows all steps in the analysis to occur in the correct sequence [55, 56]. All the components of the interface are commercially available. The injection device must... 

All inputs to the control loop (changes in set-point or disturbances) are generically represented by V(s). The input V(s) is found by passing a mathematically bounded normalized input V (s) through a transfer function block lV(s), called the input weight, as shown in Figure 9.22. 

Fig. 3.4 (c) Penn State design tip exchange setup ffor an FIM or a pulsed-laser atom-probe with a vacuum lock. The tip can be heated by passing a current through the wire loop. The tip is mounted on an internal gimbal and is cooled through a copper braid by a refrigerator. 

If 0 is induced by passing a current / through NT turns of a coil wound on the ferromagnetic loop (Fig. 6.14a), then ... 

The injector system is often of the loop type. Here the main solvent delivery tube to the column top is by-passed in a loop, which may be isolated and depressurised, and injected with sample via a septum. After injection the liquid in the loop is released into the main solvent flow. The loop volume is of comparable capacity to the injection volume. Most instruments are designed for autosampling in the case of multiple analyses, the operation being controlled by the instrument software. 

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