Pressure pulsations

The large variety of displacement-type flmd-transport devices makes it difficult to list characteristics common to each. However, for most types it is correct to state that (1) they are adaptable to high-pressure operation, (2) the flow rate through the pump is variable (auxiliary damping systems may be employed to reduce the magnitude of pressure pulsation and flow variation), (3) mechanical considerations limit maximum throughputs, and (4) the devices are capable of efficient performance at extremely low-volume throughput rates. 

Loose casing and support Pressure pulsations Vibration transmission Gear inaccuracy Valve vibration Dry whirl Blade passage... 

Safriet, B, E., Analysis of Pressure Pulsation in Reciprocating Piping Systems by Analog and Digital Simulation, ASME 76-WA/DGP-3, New York, NY American Society of Mechanical Engineers, 1976. 

Never use malleable iron fittings or pipe unless the fluid is nonhazardous and the pressure not greater than 25 psig. Always use a pressure rating at least four times that of the maximum system pressure. t lso, never use cast iron or malleable iron fittings or valves in pressure pulsating systems or systems subject to physical shock. 

All frequencies probably exist in the pressure pulsations from a compressor however, some are more basic than others and carry the greatest pressure energy peaks. 

Figure 13-23 suggests recommended pulse level (peak-to-peak) pressure pulsations for acceptable pipe vibration. Figure 13-24 presents allowable machinery and pipe vibration at safe limits and damage levels, and Figure 13-25 presents allowable pressure pulsations for various pipe spans between rigid supports when a 5 mil peak-to-peak vibration is allowed at the center of the pipe spans for the pipe sizes noted. 

Pp = pressure pulsation magnitude, peak-to-peak, psi = pulsation attenuation by area-ratio method, or... 

Note Do not use a commercial back-pressure device for this test, as this may dampen the true pressure pulsations arising from the pump. 

FIGURE 8 Example of HPCL pump power up, flow accuracy, and pressure pulsation verification document, as part of either an OQ or PQ protocol. Courtesy of PerkinElmer LAS, Shelton, CT. 

Pump Flow Accuracy and Pressure Pulsation Tests 7... 

It is recommended that OQ test the following on an HPLC system flow accuracy, pump compositional accuracy, pressure pulsations, column oven temperature accuracy/stability, detector noise/drift and wavelength accuracy, autosampler injection precision and carryover. 

Pressure pulsations for incremental flow-patterns are of the least amplitude in horizontal tubes, and increase steadily with tube inclination to become a maximum in vertical tubes. Apparently no correlations for pressure-drops which allow specifically for the effect of tube inclination have yet been developed. 

The pumping rate is controlled by piston retracts or by the cam rotating speed. The main drawback of this type of pump is sinusoidal pressure pulsations which lead to the necessity of using pulse dampers. 

In another paper Ya.B. considered2 the interaction between pressure pulsations in a powder-driven rocket chamber with supersonic flow of the combustion products and pulsations in the combustion velocity. It turned out that for small sizes of the combustion chamber self-generation of oscillations appears, leading to... 

Positive-displacement compressors (pressure pulsation and/or mechanical vibrations)... 

Pressure pulsations can make an SRV relieve below set pressure when the pressure spikes perhaps reach set pressure. These spikes have such high frequency that they are unseen on charts or gauges. Nevertheless, they do art on the SRV, making it vibrate at high frequency. 

Figure 6.22 shows how a sharp-edged SRV inlet entrance can induce pressure pulsations (vortices) that apparently make the SRV relieve low, leak severely and/or wear out prematurely. 

Pressure pulsations caused by sharp-edged nozzle entrances... 

Since all pressure generators in high pressure process technology cause pressure pulsations in the plant, for a trouble-free operation pulsation reducing measures are necessary. 

The pulsation of volume flow leads to pressure pulsations in the following piping system. Their size depends on the geometry of the piping system and the fluid parameters. The relevant effects on pressure pulsations are summarized in table 1. 

Influences on pressure pulsations in high pressure plants... 

A disadvantage of damping flow pulsations by orifices is the additional pressure loss brought into the system. So the obtainable reduction in pressure pulsation is quite limited. 

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