Volumetric metering pump

When solution must be pumped, consideration should be given to use of holding tanks between the dry feed system and feed pumps, and the solution water supply should be controlled to prevent excessive dilution. The dry feeders may be started and stopped by tank level probes. Variable-control metering pumps can then transfer the alum stock solution to the point of application without further dilution. Means should be provided for calibration of the chemical feeders. Volumetric feeders may be mounted on platform scales. Belt feeders should include a sample chute and box to catch samples for checking actual delivery with set delivery. Gravimetric feeders are usually furnished with totalizers only. Remote instrumentation is frequently used with gravimetric equipment, but seldom used with volumetric equipment. 

The amounts are adjusted either by volumetric metering or mass-flow metering [85], Solid ingredients must first be solubilized, to be metered with a pump (in the batch process, they are directly added into the mixer). 

In the volumetric metering approach, the quantities are determined through the pumps used to send them to the mixing lines. Densities of all raw materials must be known under the particular conditions of temperature and formulation, and the accuracy of the pumping rate regularly checked to get the right mass flow rate from the volumetric flow rates. 

Equipment used to manufacture RIM products must be extensively rebuilt to process RIM nylons. Because the viscosity of nylon RIM systems is low and the ingredients are quite reactive, leakage at the seals and the volumetric efficiency of the metering pumps (that is, the amount of material actually pumped divided by the volume displaced by the metering pumps) may cause problems, which require special attention. Hence, most manufacturers recommend having the machine designed specifically for nylon RIM systems. 

Positive displacement meters—direct volumetric totalizers—are often used in laboratories for calibration. The principle is based on delivering a discrete volume of fluid in aliquots. In fact, water wheels and shadoofs could be considered as positive displacement meters. Pumps may also be considered as meters. 

Typical equipment used to make PET fibers is shown in Figure 6. Prior to melting, the polymer chips must be thoroughly dried, t5q)ically under vacuum at elevated temperature for several hours. The equilibrium moisture content of PET imder ambient conditions is about 0.5% (11) and this much moisture would cause imacceptable levels of depolymerization. The dried polymer chips are fed to an extruder which melts the chips and forwards them to a metering pump, which delivers a volumetrically controlled flow of polymer into a heated spinning pack. 

For metering, suitable devices are used, such as various types of balances containers or weigh hoppers, belt weigh types, etc., for gravimetric weighing or travelling band conveyer or screw conveyer for solid materials and rotameters, piston pumps, etc., for liquid components, in the case of volumetric metering [44]. 

A standard gear pump can have one or more exit streams as needed. Each stream has a constant volumetric output based on the rotational speed (RPM) of the gears. The gear pump is driven by an AC motor with inverter or vector drive speed control. The exit pressure from a metering pump in a typical spinning process will range from approximately 7000 kPa (1000 psi) to 25 000 kPa (3500 psi). Once the pressure reaches 25 000 kPa (3500 psi), the process is typically shut down and the filter media replaced. 

Another efficiency which is important for positive displacement pumps is the volumetric efficiency. This is the delivered capacity per cycle as a percentage of the true displacement per cycle. If no slip occurs, the volumetric efficiency of the pump is 100 per cent. For zero pressure difference across the pump, there is no slip and the delivered capacity is the true displacement. The volumetric efficiency of a pump is reduced by the presence of entrained air or gas in the pumped liquid. It is important to know the volumetric efficiency of a positive displacement pump when it is to be used for metering. 

Flow Rate Accuracy. One of the key performance requirements for the pump module is the ability to maintain accurate and consistent flow of the mobile phase. This is necessary to provide stable and repeatable interactions between the analytes and the stationary phase [8,9]. Poor flow rate accuracy will affect the retention time and resolution of the separation. The flow-rate accuracy of the pump can be evaluated simply by calculating the time required to collect a predetermined volume of mobile phase at different flow rate settings. For example, the flow-rate accuracy at 2 mL/min can be verified by using a calibrated stopwatch to measure the time it takes to collect 25 mL of effluent from the pump into a 25-mL volumetric flask. A calibrated flow meter can be used to determine the flow rate as well. The typical acceptance of the flow rate accuracy is listed in Table 11.1. A steady backpressure may be required, depending on the requirement of the system. 

Starch slurry make-down systems are designed to prepare a uniform suspension, using batch or continuous systems. In modem paper mills, automated batch or continuous systems are used. Water content and bulk density will affect the flow of dry starch.90 In the batch slurry system, weighed increments of starch are drawn from the silo and periodically added to a measured quantity of water in the make-up tank. The suspension is screened and automatically pumped to a larger storage tank on demand by a level transmitter. Continuous make-down of starch slurry is accomplished by simultaneously feeding starch and water at controlled rates into the slurry make-down tank. The dry starch is metered with a volumetric screw feeder. The slurry is screened before dispersion by batch or continuous cooking. 

Two-part adhesives are generally dispensed by volumetric pumps for semiautomated and automated medium- to high-volume assemblies. Metered dispensing systems are easily capable of processing adhesives with mix ratios of 1 1 up to 15 1. 

Because volumetric rather than mass metering instruments are typically employed on actual treatments, conversion from standard condition gas injection rates to pumping condition liquid rates must be performed. Figures 8 and 9 can be used to estimate the pumping requirements at liquid conditions. 

Figure 13-6 Apparatus for RESS A = SCF reservoir PV = high pressure volumetric pump HI, H2 = heat exchangers V, VI, V2, V3 = on-off valves S = saturation vessel EN = expansion nozzle E = expansion vessel F = flow meter G = rotameter PI = pressure indicator TI = thermometer.

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