Positive displacement pump fluid flow

The ease with which the separated products leave the bowl determines the richness of the fat. Fluid whole milk enters the separator under pressure from a positive displacement pump or centrifugal pump with flow control (Fig. 1). The fat (cream) is separated and moves toward the center of the bowl, while the skimmed milk passes to the outer space. There are two spouts or oudets, one for cream and one for skimmed milk. Cream leaves the center of the bowl with the percentage of fat ( 30 40%) controlled by the adjustment of a valve, called a cream or skim milk screw, that controls the flow of the product leaving the field of centrifugal force and thus affects the separation. 

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. 

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. 

The binder solution is delivered to the nozzle port through a spray lance and tubing (Fig. 7b). The peristaltic, or positive displacement, pump is conunonly used to pump the binder solution. The pneumatically controlled nozzle needle prevents the binder liquid from dripping when fluid flow is stopped. Nozzle port openings 0.8 and 2.8 mm in diameter are most common and are interchangeable. 

In positive displacement pumps, a discrete parcel of fluid is taken from the pump inlet to the pump outlet where it is discharged. This continues even if there is substantial resistance to flow at the outlet. Positive displacement pumps may develop very high pressures and pressure relief devices should be fitted. 

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. 

Figure 2.1-6 (a) Small-volume reciprocating pump head. Single ball check valves are used for controlling the air/fluid flow (Superpressure Inc.), (b) Laboratory scale positive displacement pump (syringe pump High Pressure Equipment Co.). 

Positive-displacement pumps work by trapping a fluid in a cavity and then squeezing it out at a higher pressure they are generally high-pressure-rise, low-flow-rate devices. 

Linear peristaltic pumps transport fluid through a flexible duct using traveling contraction waves. In a typical linear peristaltic pump, discrete translational elements rhythmically compress a straight section of flexible tube, moving fluid volumes. In contrast to rotary peristaltic pumps, linear peristaltic pumps usually do not use rollers or sliding contact elements. Because a moving boundary displaces fluid and induces the flow, linear peristaltic pumps are an example of positive-displacement pumps. 

One of the earliest types of rotary micropumps developed for microfluidics applications, drug delivery in particular, is the jet-type magnetically driven fluid micropump. It is based on a rotary micromotor which is attached to a toothed rotor (Fig. 1). Basically, it is a micro version of conventional positive displacement pump. Flow rates up to 24 pL/min at a pressure of 10 kPa have been obtained using this design [4]. 

More recently, HNP Mikrosysteme GmbH [14] has commercialized a type of rotary pump called micro annular gear pump. This t3q>e of pump is a positive displacement pump with an externally toothed rotor and internally toothed ring, which are assembled with a small eccentricity of their rotation axes with respect to each other. The rotation of the internal rotor forces the fluid pockets which are interlocked between two gears to flow. The pump flow rates vary from product to product, but are in a range of 1 pL/h to 1.2 1/min. Advantages of this product include accurate control of flow rate and minimum pulsation in delivery. 

Huid power is the product of flow rate by head. In an ideal positive displacement pump, flow rate is independent of head. Therefore, the maximum fluid power is approximately P = p Q = p ct V/3T. One actuator closes at each step, and two actuators must be held closed at each step. If energy act is required to close an actuator, and power / act is required to hold it closed, we see that each cycle requires total energy 3 act + PactT (we assume no energy is required to open an actuator). The total power consumed per cycle is (fiact/7) + 2/ aot> and the maximum efficiency is r] = pact W(3 act + 6PactT). 

The fluid is pumped to the sandstone core by a twin cylinder Ruska Pump, This is a constant volumetric positive displacement pump which will deliver fluid at a constant flow rate (0-240 cc/hr) against a pressure of up to 2000 psi. The cylinders are stainless steel, to avoid potential corrosion problems. Immediately following the pump are two Millipore filters which will trap any suspended particles larger than 0,45y that might be in the fluid. 

The Pioneer Figure 7) peptide synthesis system (42) was introduced recently as a successor to the 9050Plus instrument, which was first commercialized in 1988. The Pioneer combines dual simultaneous column capability with a high throughput multiple peptide synthesis option (discussed in Section 4.1). It is an Fmoc/rBu continuous-flow system that in its standard mode of operation functions with two columns operating simultaneously with independent control of solvent, reagent, and amino acid delivery. Fluid flow is via programmable positive displacement pumps that deliver with a flow rate of up to 50 ml/min and require no flow-rate calibration. Each column can function... 

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