Pumps positive displacement metering

The core - flood apparatus is illustrated in Figure 1. The system consists of two positive displacement pumps with their respective metering controls which are connected through 1/8 inch stainless steel tubing to a cross joint and subsequently to the inlet end of a coreholder 35 cm. long and 4 cm. in diameter. Online filters of 7 im size were used to filter the polymer and brine solutions. A bypass line was used to inject a slug of surfactant solution. Two Validyne pressure transducers with appropriate capacity diaphragms are connected to the system. One of these measured differential pressure between the two pressure taps located about one centimeter from either end of the coreholder, and the other recorded the total pressure drop across the core and was directly connected to the inlet line. A two - channel linear strip chart recorder provided a continuous trace of the pressures. An automatic fraction collector was used to collect the effluent fluids. 

The direction and flow rate of the test and hydraulic fluids are determined by nine three-way valves and six a1r-dr1ven hydraulic pumps that must be sequenced 1n the proper order. The position of the valves 1s determined by six air-driven actuators. Two of the pumps are miniaturized, air-driven, hydraulic pumps used for sample loading and pressurization. One of the remaining four pumps 1s a high-pressure, constant volume, positive displacement, piston metering pump to provide hydraulic pressure, and the other three are positive displacement syringe pumps for In-line addition of additives. 

In general positive displacement pumps have limited flow capacity but are capable of relatively high pressures. Thus these pumps operate at essentially constant flow rate, with variable head. They are appropriate for high pressure requirements, very viscous fluids, and applications that require a precisely controlled or metered flow rate. 

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. 

Methanol or dimethyl ether feeds were fed from an ISCO positive-displacement pump. Liquid products were collected in a room-temperature trap and gaseous products were analyzed by on-line gas chromatography and volumes measured by a wet-test meter. The catalyst could be regenerated in-situ by switching to a nitrogen/air mixture. 

Diaphragm pumps are used for metering small amounts of additive into a fuel or fuel oil. The cost of these pumps is low compared to other positive displacement pumps. These pumps are excellent metering pumps and are primarily designed for low-pressure, low-flow applications. Also, they are not recommended for pumping high-viscosity fluids. 

Kinetic Studies. Peracetic Ac id Decomposition. Studies with manganese catalyst were conducted by the capacity-flow method described by Caldin (9). The reactor consisted of a glass tube (5 inches long X 2 inches o.d.), a small centrifugal pump (for stirring by circulation), and a coil for temperature control (usually 1°C.) total liquid volume was 550 ml. Standardized peracetic acid solutions in acetic acid (0.1-0.4M) and catalyst solutions also in acetic acid were metered into the reactor with separate positive displacement pumps. Samples were quenched with aqueous potassium iodide. The liberated iodine was titrated with thiosulfate. Peracetic acid decomposition rates were calculated from the feed rate and the difference between peracetic acid concentration in the feed and exit streams. 

Fig. 3 shows the experimental apparatus. The feed tank had a 50 gallon capacity and was equipped with a variable speed mixer. The feed pump was a flexible impeller, positive-displacement pump to minimize shearing of the feed emulsion. The pumping rate was regulated by a Graham Variable Speed Transmission. Each flotation tank was 11.5 in. ID with 6.5 in. liquid depth maintained by a CE IN-VAL-CO conductometric level controller with a pneumatically actuated control valve in the effluent line. The fourth cell was not equipped with an air inducer. The outer diameter of the air downcomers was 1.5 in. The rotor in each air inducer was a turbine taken from a 2 in. turbine flow meter. Each rotor was belt driven by a 10,000 rpm, 1/30 hp motor and all three motors were governed by the same variable transformer. Another pulley on each rotor shaft was attached to a non-powered belt connecting all three shafts to ensure that each rotor turned at the same speed. 

Dosing relates to the various methods of applying chemical product to the cooling system. Dosing is normally proportional to the makeup water demands or the system volume, and the most common method is via the use of positive displacement, diaphragm metering pumps. 

Rotary positive-displacement pumps with no valve action gear pumps, lobe pumps, screw pumps, eccentric-cam pumps, metering pumps... 

In the feed section, the mainly l--hexene reactant (98.60% 1-hexene, 0.95% cis-3 hexene, 0.25% trans-2 hexene and 0.15% cis-2 hexene, supplied by Ethyl corporation) is introduced from an Instrumentation Specialties Company (ISCO) model 314 metering pump into a flowing stream of liquefied COo. The l-hexene/C02 mixture is then fed to a high pressure positive displacement pump contained in the SCESS. In this pump, fluids can be pressurized up to 6,000 psig and total flow rate can be adjusted between 46 ml/hr and 460 ml/hr. Since feed to the pump must be in a liquid state, both the l-hexene/C02 mixture and the pump head are sufficiently cooled by circulating chilled water at 5 C. The system pressure is controlled by means of an adjustable back pressure regulator. 

Reactor and Reactor Conditions. A 5-litre glass reactor (15 cm diameter) fitted with four stainless steel baffles (10 cm x 1.5 cm) immersed in a thermostatted oil bath at 80 °C (reflux temperature of methyl acrylate) was used for polymerisation. Stirring was by means of a marine type impeller (6 cm diameter and pitch 45°). The overall reaction rate was sufficiently slow to ensure isothermal conditions. Additions of solutions of the more reactive monomer (styrene, of molar concentration 0.8) to the reactor were made using a computer controlled positive displacement pump (Precision Metering Ltd.) with four long-stroke pump heads, 90 out of phase to minimise pulsation of the flow. 

Flow. Nonintrusive sensors that can be maintained at the process temperature are ideally suited to measure the flow rate of feed and product streams. Magnetic flow meters are suitable and inexpensive choice for aqueous streams. Organic streams with low dielectric constants require a vibrating tube mass flow meter to satisfy these criteria. Although commonly installed, flow meters that operate by inducing a pressure drop proportional to the flow rate present restrictions for solids accumulation that may alter the calibration. An alternative approach is to monitor the rotational speed of a positive displacement pump. Accuracy of this method is subject to wear and tolerances in the pump. 

Continuous nitration demands accurate metering and control equipment. Such equipment as positive-displacement pumps, constant-head orifice flow controls, and rotameters are common accessories to continuous nitrators. 

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