Multi-port valves

The run and regeneration cycle on small to medium-size units is normally governed by a multi-port valve, which is the only moving part required. There have been many cases where this has failed and brine was injected directly into the boiler. A conductivity meter on the make-up line would guard against this. 

The parallel reactor for the screening of the titer-plates consists of several modules, each of them is responsible for just a single operation (Fig. 4.12). The gas flow for example is preheated and evenly distributed within the distribution module and delivered to the wells on the titer-plate. The latter is clamped between the distribution module and the insulation module and also treated as a separate reaction module. The insulation module separates the heated section of the parallel reactor from the unheated section and is further cooled by the heat exchanger module on top of it. The last module, just above the heat exchanger module, is a multi-port valve that delivers the product gas to the gas-chromatograph. 

Multi-port Valves, Injection Valves and Sensors... 

Multi-port valves belong to the key components in screening. Most equipment for analysis exists only in single-channel versions. Exceptions are, for example, radiation beam measurements of Atkins and Senkan [114] and tools for parallel analysis at Symyx. As long as equipment for parallel analysis does not exist for every type of desired measurement, multi-port valves will always be an essential part of every screening device. 

The optimum process for this binary separation would be to have fixed positions for the introduction of mobile phase and feed, and fixed collection points for the two components of the mixture whilst having the ability to move the stationary phase upwards. In practice it is impossible to engineer a system where the column bed moves, but it is possible to simulate the movement. Such a system is shown schematically in Figure 1.6 where four columns are set in sequence with four multi-port valves between the columns. 

Multi-Port This term refers to any valve or manifold of valves with more than one inlet or outlet. For throttling control, the three-way body is used for blending (two inlets, one outlet) or as a divertor (one inlet, two outlets). A three-way valve is most commonly a special globelike body with special trim that allows flow both over and under the plug. Two rotary valves and a pipe tee can also be used. Special three-, four-, and five-way ball-valve designs are used for switching applications. 

For in situ reaction studies, an IR cell which approximates a continuously stirred tank reactor (volume = 1.5 cm ), equipped with 1/16" gas in- and outlet tubing and CaF2 windows, was used [12]. For the characterization of the surface species in the zeolite pores during the reaction, time resolved IR spectra of the catalyst were recorded as the activated zeolite was contacted with a He stream containing the reactants. Simultaneously, samples of the effluent gas stream were collected in sample loops of a multi port valve and subsequently analyzed by gas chromatography. This allowed to directly compare the type and concentration of the surface species with the rate of the catalyzed reaction. 

The multi-port selection valve of a sequential injection analyser can be regarded as an advanced commuting device, which selects one inlet port to be commuted to any one outlet port at a time. Also, the entire manifold can be accommodated in such a valve, leading to the lab-on-valve concept [84]. 

The basic components of the system are a liquid driver with only one carrier stream, a multi-port selection valve and a detector (Fig. 2.9). The valve is the heart of the sequential injection system and normally comprises 6—10 peripheral ports and a central port in a multi-position valve configuration. The central port is linked to a holding coil and the peripheral ports are connected to different solution aspiration tubes and transmission lines that are linked to different manifold components, e.g., detector and mixing chamber. Only one peripheral port is connected to the central port at any one time. Stream management inside the holding coil is accomplished by a bi-directional piston (or peristaltic) pump. The analyser is fully computer controlled and the injection volumes, residence times, delivery of solutions and analytical path lengths are selected based on a valve timing sequence and related flow rates. 

K. Yasuda, T. Kuroishi, Magic of multi-port valve for flow injection analysis, J. Flow Injection Anal 6 (1989) 5. 

A pipe DN 80 (88.9 mm outer diameter) is equipped with a lagging of thickness of 4.1 nun. Normally steam at 150 °C passes through it. An operator mistakenly exposes the pipe to steam of 175 °C by placing a multi-port valve into a wrong position. An interlock, which would have prevented this, is not installed. The ambient temperature is 20 °C. Is self-ignition (at 181 °C) to be expected ... 

A variation of flow-injection analysis, sequential-injection analysis (SIA), has recently been introduced. Contrary to flow-injection analysis, where the components are injected into a continuous flowing stream, in SIA injections are done sequentially directly into the reactor/detector system. The instrumental setup usually consists of a syringe pump in combination with an electronically controlled multi-port valve. SIA systems have been shown to be more flexible regarding injection volumes and injection times. This technology has been demonstrated to be very efficient for carrying out immunoassays. Both fluorescence and chemiluminescence immunoassays have already been carried out with this technique. 

Both types can be made in multi-port form, that is the hole in the ball or plug may be T or L shaped and the valve body has three or four outlets (Fig. 3.15). The careful selection of a single, multi-port valve will not only eliminate two or three valves but it will also eliminate the dead leg of material that remains in a branch above the conventional valve (Fig. 3.16). 

Since the columns must be interchangeable, the full set of connections must be provided on them all, and this involves a fairly extensive set of control valves. Since the start of one feed corresponds precisely with the cessation of another, it is convenient to employ multi-port valves, and various mechanical designs are available. These may be manually operated or may be driven by motors controlled by time switches if operating on a constant time cycle and with constant flow rates. A poppet valve assembly of this type is shown in Fig. 3.5. If each cycle must be unique to cope with variations of feed concentrations, etc., it is possible in some processes to control the motorized valve assemblies by means of automatic analysers on the effluent, eluent and wash streams. Instrumentation of this type can only be installed after very thorough development trials with process solutions under a wide variety of anticipated operating conditions, if reliable operating results are to be obtained. 

This equipment is not known to have been used on an industrial scale and it probably achieves little which could not be equally well engineered by a conventional column plant controlled automatically to a fixed time cycle, using a system of multi-port valves. It has the disadvantage that a high proportion of the essential part of the plant is continually in motion, with the attendent mechanical engineering problems which this implies. 

The experimental apparatus consists of a gas flow system with a four-port valve, a multi-reflection Attenuated Total Reflection (ATR) accessory (Pike Technologies), and a custom reactor manifold mounted to the ATR top plate, shown in Fig. 45.1. The ATR reactor manifold consists of (i) a Cap2 window for UV irradiation, (ii) an inlet and outlet port, and (iii) an injection port for the liquid phase reactant. 

Figure 6. Schematic diagram of instrumentation used to perform the multi-dimensional 1C. (a) 10-Port valve positions for detection of 2nd dimension separation (i.e. effluent from column 2 diverted through conductivity detector 2). (b) 10-Port valve positions for injection of 2 dimension cut fractions onto 3 dimension column with subsequent detection using conductivity detector 2 [12],...

Autofill Valve. The VALCO autofill valve and actuator is an option available on the Suprex Model 50 extractor that presented problems during routine operation even without the multi-vessel adaptations. With the multi-vessel option, rapid refill of the syringe pump is a necessity for routine unattended operation. This is accomplished via a VALCO 1/16 five port valve (Model E04) mounted on an electric actuator. The valve has a pressure rating of 11,000 PSI. In the tank mode, the autofill valve directs flow from the mobile phase tank to the pump. In the column mode, flow is directed from the pump to the column. 

In spite of its favourable characteristics, relocation of manifold components has not been widely exploited, being restricted to some laboratories in Portugal, Spain and Brazil. This is perhaps due to a misunderstanding that the system is somewhat sophisticated and requires specific components. On the contrary, simple commercially available components (e.g., the widely used six-port rotary valve) are used for accomplishing multi-commutation. 

An attractive alternative is the use of the multi-position selecting valve (Fig. 2.10), usually with 6, 8,10, or 12 outer ports and a common central port [15]. Selection valves are inherent to sequential injection analysis and... 

Nitrogen speciation has been facilitated with the introduction of SIA, which allows multi-parametric determinations with simpler instrumental setups and reduced reagents consumption [165-169]. SIA systems using the Griess reaction have been exploited for determination of nitrite and nitrate in natural waters, wastewaters, vegetables, dairy products, and soils with incorporation of the solid-phase reactor either on one port of the selection valve or in the holding cod. 

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