Reciprocating pump characteristics

For the most part, positive displacement pumps can be classified either as rotary pumps or as reciprocating pumps. However, pumps do exist which exhibit some of the characteristics of both types. 

It is important to describe how fluids are propelled, as well as the main liquid drivers such as peristaltic pump [1], piston pump [89], reciprocating pump [154], gas propeller [25] or other strategies for this task, e.g., kinematic focussing [155] or gravity [156]. The peristaltic pump is by far the most common device for propelling fluids in flow analysis therefore, the absence of any information assumes the use of such a pump. Characteristics of the pump tubing are mentioned in most publications, but this information is not needed unless there is an incompatibility with the propelled fluids. 

A reciprocating pump (Fig. 6) consists of three main parts the motor, the drive mechanism and the pump head through which the solvent is flowing, Usually the pump head can be dismantled from the remainder of the pump and sometimes replaced with another pump head with different characteristics. 

The NPSHr of reciprocating pumps is usually calculated for incipient cavitation conditions from the maximum entry pressure losses [18, 19], which are largely dictated by the characteristics of the suction check valve. The manufacturer s NPSHr data are in general based on these fluid mechanical effects. Typical values for the NPSHr range between 1 and 3 m for liquid CO2 (this corresponds to a pressure requirement of between 0.1 and 0.3 bar). 

Figure 9.19 Performance curves and control characteristics of pumps, (a) Differential pressure Ap as a function of volumetric flow rate V. Curves Ca and Cb are performance curves for a centrifugal pump at rotation rates /ia and /Ib respectively. Curve 0 is for a reciprocating pump. Curves a and b give the installation characteristic for the operation points A and B. (b) Volumetric flow rate (delivered by reciprocating pump) as a function of stroke frequency, /i, at constant stroke length hp or of stroke length at constant stroke frequency.

The reciprocating and rotary positive displacement pumps primary characteristic is that they have a nearly direct relationship between the motion of the pumping... 

A central component of the LC instrument is the pump, for its characteristics can strongly influence an analysis (e.g., flow reproducibility). The three principal types of systems— pneumatic, syringe type and reciprocating piston—have been reviewed in the literature (18-20). 

Pulsation can be problematic ancfdifficult to predict. Pulsations are also dependent on acoustic resonance characteristics. For reciprocating equipment, such as reciprocating compressors and pumps, in some cases, an analog (digital) study needs to be performed to identify the deficiency in the piping and pipe support systems as well as to evaluate the performance ofthe machine during operation. The study will also provide recommendations on how to improve the machine and piping system s performance. 

The laser used to generate the pump and probe pulses must have appropriate characteristics in both the time and the frequency domains as well as suitable pulse power and repetition rates. The time and frequency domains are related through the Fourier transform relationship that hmits the shortness of the laser pulse time duration and the spectral resolution in reciprocal centimeters. The limitation has its basis in the Heisenberg uncertainty principle. The shorter pulse that has better time resolution has a broader band of wavelengths associated with it, and therefore a poorer spectral resolution. For a 1-ps, sech -shaped pulse, the minimum spectral width is 10.5 cm. The pulse width cannot be <10 ps for a spectral resolution of 1 cm . An optimal choice of time duration and spectral bandwidth are 3.2 ps and 3.5 cm. The pump pulse typically is in the UV region. The probe pulse may also be in the UV region if the signal/noise enhancements of resonance Raman... 

A Throttling characteristics of centrifugal (c) -and positive- displacement (e, reciprocating d, rotary) pumps. B Control characteristics of positive displacement pumps a,b, Systems characteristics (b, after speed control) VFluid flow Ap, Differential pressure n, Speed h, Stroke length A, B, B, Operating points. 

Figure 5.7 shows that positive-displacement compressors, like vacuum pumps, are divided into two main classes reciprocating and rotary. Table 5.4 lists characteristics of these compressors. Ludwig [14] discusses compression equipment and calculation methods in detail. 

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