The proportioning pump

A commercial pump supporting 24 tubes (Ismatec, Switzerland) is shown in Fig. 10-17. 

This peristaltic pump uses a roller wheel with a planet drive, i.e., each roller is driven actively to reduce the frictional wear on the tubes. The pump allows the pressure of the roller to be adjusted individually for each tube. The lifetime of a tube is 100-200 h of continuous operation depending on the corrosive action of the reagent on the tubing material. As the frictional wear acts mainly on the roller side of the tubes, turning them over after about half the lifetime may reduce the risk of the tube breaking. 

Colour code Inner diameter (in) Flow rate mL/min 

Remarks The pumping volumes depend on the speed of the peristaltic pump. The values listed refer to a standard speed which is the fixed speed (or one of those selected) of most peristaltic pumps which these tubes fit geometrically. 

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The proportioning pump controls the rate of advancement, viz 10 inch/minute, of each sample through the analysis stream. Hence, a fixed length of tubing is equivalent to a fixed amount of time. Each analysis stream is made of transparent plastic flexible tubing, and each patient-sample is separated from one another by an air-bubble. 

Method. A diagram of the apparatus is shown in Fig.4.29. Any suitable liquid chromatograph may be used. The AutoAnalyzer is modified such that the liquid sampler is fitted to the end of the chromatographic column. The proportioning pump is by-passed. The set-up of the AutoAnalyzer is the same as that for normal measurements of cholinesterase. The application of this technique to the determination of CGA 18809 in plum-leaf extract is shown in Fig.4.30. A comparison is made with UV analysis of the same extract. The limit of detection for CGA 18809 is c . 20 ng at a 3 1 signal to noise ratio. The relative inhibitions of several organophosphates and carbamates are compared in Table 4.9. Diazoxon may be detected in low picogram quantities. 

Change in the position of the sorption front, which is in the part of the column positioned between electrodes, results in bridge imbalance that is registered by a potentiometer. Divergence of the needle, as a result, breaks the contact and a relay reacts. Resistance is increased if the sorption front has risen. If the front has lowered, resistance is reduced. Response of the electric motor of the proportional pump controlling solution flow in response to such signaling with respect to sorption front... 

The instrumentation used is part of the AutoAnalyzer system manufactured by Technicon, Inc. 19), The AutoAnalyzer modules required are the sampler, the proportioning pump, the colorimeter with range expander, and the recorder. The AutoAnalyzer sampler alternately delivers sample solution and cleansing water from a small reservoir. The quantity of sample is controlled by the sampling rate, adjusted by means of a cam on a clock mechanism, and by the diameter of the sample tube on the manifold of the pump. 

Fig. 2. Flow sheet of lecithin producing unit. Crude soybean oil is heated in the preheater, 1, to 80°C, mixed with 2% water in the proportion control unit, 2, and intensively agitated in 3. The mixture goes to a dweUing container, 4, and is then centrifuged after a residence time of 2—5 min. The degummed oil flows without further drying to the storage tanks. The lecithin sludge is dried in the thin-film evaporator, 6, at 100°C and 6 kPa (60 mbar) for 1—2 min and is discharged after cooling to 50—60°C in the cooler, 8. 9 and 10 are the condenser and vacuum pump, respectively.

There are three basic requirements that Hquid level control devices are designed to satisfy alarm functions, pump/valve control, and transmitted output signal to track level continuously. Alarm devices provide warning or shutdown functions when process levels pass a predeterrnined point in the vessel pump /valve control devices turn on/off pumps or open/close valves at predeterrnined levels in the vessel and transmitters provide a proportional output signal over a predetermined span to send to a local meter or signal back to a control room. 

In a submerged-tube FC evaporator, all heat is imparted as sensible heat, resulting in a temperature rise of the circulating hquor that reduces the overall temperature difference available for heat transfer. Temperature rise, tube proportions, tube velocity, and head requirements on the circulating pump all influence the selec tion of circulation rate. Head requirements are frequently difficult to estimate since they consist not only of the usual friction, entrance and contraction, and elevation losses when the return to the flash chamber is above the liquid level but also of increased friction losses due to flashing in the return line and vortex losses in the flash chamber. Circulation is sometimes limited by vapor in the pump suction hne. This may be drawn in as a result of inadequate vapor-liquid separation or may come from vortices near the pump suction connection to the body or may be formed in the line itself by short circuiting from heater outlet to pump inlet of liquor that has not flashed completely to equilibrium at the pressure in the vapor head. 

Equation (18-36) is the general expression for impeller-induced nucleation. In a fixed-geometry system in which only the speed of the circulating pump is changed and in which the flow is roughly proportional to the pump speed, Eq. (18-36) may be satisfactorily replaced with... 

Pressure drop under streamline flow conditions is directly proportional to the quantity of oil flowing. The effect of reduced flow rate after take-off points, as compared with full flow rate throughout the full length of the pipeline when there is no take-off, should be taken into account to ensure that variation in pressure is within the specified pump output. Special consideration is necessary with gravity and ring main systems serving several take-off points. 

The flow loss in a system varies as (velocity) or (flow rate), so the total loss imposed by a system on a pump can be shown to vary with flow rate in the way shown in Figure 32.38(a). Figures 32.38(b) and 32.38(c) illustrate how system curves vary with the proportions of static and dynamic losses. 

Unfortunately, neither the computer nor the potentiometric recorder measures the primary variable, volume of mobile phase, but does measure the secondary variable, time. This places stringent demands on the LC pump as the necessary accurate and proportional relationship between time and volume flow depends on a constant flow rate. Thus, peak area measurements should never be made unless a good quality pump is used to control the mobile phase flow rate. Furthermore, the pump must be a constant flow pump and not a constant pressure pump. 

The ACTIV-OX chlorine dioxide system evaluated in this trial overcomes many of the problems associated with chlorine dioxide for the small water user. A chlorine dioxide precursor solution and a dilute acid solution are mixed in a 1 1 ratio immediately prior to injection into the water to be treated. The dose rate of chlorine dioxide is controlled by water meter signal to two proportioning pumps. The mixing of the two chemicals immediately produces a chlorine dioxide solution which is diluted to the required strength by injection into the water to be treated (Fig 3). 

Figure 12.6 illustrates the outline of such an analysis. An automatic pipette extracts a preset volume of the liquid sample (or solution) from a cup presented to it on a turntable. The measured sample is mixed with the reagents in the appropriate proportions, and propelled through the instrument by the peristaltic proportioning pump. This pump operates by means of moving bars, attached to a chain drive, which sequentially compress the plastic sample and reagent tubes to drive the liquids forward through the instrument. The incorporation of a succession of air bubbles at... 

This particular section of the Auto Analyzer consists mainly of the sampler, proportioning pumps, and programmer. First, the sampler introduces a fixed quantity of serum sample into the analysis train , which varies from one instrument to another instrument supplied by different manufacturers. For instance, the SMA-12 Survey Auto Analyzer possesses 12 analysis trains or streams as illustrated in Figure 2.7. 

The continuous flow process shown in Figure 4—2 has a mixture of benzene, cyclohexane, and hydrogen being heated to about 4Q0°F, pressured to about 400 psi, and pumped through the first reactor. The proportions of each feed depend on the type of catalyst being used. On a once-thro ugh basis, about 95% of the benzene is converted to cyclohexane. 

Fig. 5.14. The principles of CFA and FIA. For details see the text. 1 - sampling device 2 - proportioning pump 3 - mixing spiral,...

The disadvantages are that fuel and oxygen must be premixed. The proportions are such that the mixture may be flammable or even explosive, particularly if small variations (e.g. as a result of pumping and vaporizing liquid fuels) are possible. 

Boyle s experiments with the vacuum pump ceased in 1662, when Hooke moved to London to become curator of the Royal Society. However, by this time, Boyle and Hooke had performed a number of additional experiments that are described in the second edition of Spring of the Air, published in 1669. Included in the second edition was a statement of what is now known as Boyle s law the pressure of a gas is inversely proportional to its volume. In other words, if the pressure is doubled, the gas is compressed to one-half of its former volume and if the pressure is halved, the volume doubles. 

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