Positive displacement pump pulsation

Use centrifugal pumps. If positive displacement pumps must be used, these pumps must be fitted with approved pulsation dampening equipment surge tanks may also be required, particularly for very short and very long pipe runs. 

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. 

Positive displacement pumps. The minimal shear operation of progressing cavity or lobe pumps make them ideal for slurries. The non-pulsating flow is beneficial in most processes, but they are significantly more expensive and less portable than diaphragm pumps. 

Diaphragm pump Precise flow control Only true positive-displacement pump For low flow applications Must manage pulsation... 

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. 

Sliding vane. Positive displacement pumps in which a multi-bladed impeller rotates inside an eccentric pump cavity. They are self-priming and deliver a non-pulsating flow. 

The pulsations of a positive displacement pump are transmitted to the slurry. To prevent their propagation to the pipeline and its support, it is essential to install hydraulic dampeners (Figure 9-14). 

Vetter, G. and Schweinfurter, F. (1989) Computation of Pressure Pulsations in Pumping Systems with Reciprocating Positive Displacement Pumps, in Proc. 3rd Joint ASCEIASME Mech. Conf. San Diego, Pumping Machinery, pp. 83-89. 

There are two principal classes of pumps positive-displacement and centrifugal. In positive-displacement pumps, a given volume of fluid is mechanically forced from the suction port to the discharge with every rotation of the shaft. In reciprocating pumps, this is done in a periodic fashion, such that outflow pulsates if multiple cylinders are used, they are phased so as to diminish the amplitude and period of the pulsations, smoothing the flow. Often an air chamber is attached to the discharge line to help absorb these pulsations. 

For small feed rates, it may be considerably cheaper to use a positive-displacement pump (piston type). Control may be by stroke adjustment on a constant-speed pump as shown by Figure 5.2A or by adjustment of a variable-speed drive of a pump with a fixed stroke as shown by Figure 5.2B. If the minimum stroke rate is at least three times the reciprocal of the feed-tray holdup time, no pulsation damper is required. 

On systems with positive displacement pumps, location after the pulse dampener or bubble trap is preferred to reduce the likelihood of erratic readings due to pulsation. 

The Perkin-Elmer Model 604 liquid chromatograph (Fig.3.31) has a reciprocating pump with positive displacement. The delivery of a constant volume is digitally controlled from flow-rates of 0.05 ml/min to 6.0 ml/min at pressures of up to 7000 p.s.i. Solvent pulsations are removed by means of a damper system. 

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