Pulse piston operation

Weber (1973) has put forth a rather simple approach to pulsed piston modeling which couples the gas and solid behavior. The expression that Weber suggested is given in Eq. (9). One notes that this expression has an exponential decay of the pressure as the plug length decreases. This behavior has often been seen in industrial operations. 

Its operation ean be seen as analogous to a meehanieal flywheel and a one-piston engine. The L-C Alter, like the flywheel, stores energy between the power pulses of the driver. The input to the L-C Alter choke input filter) is the ehopped input voltage. The L-C Alter volt-time averages this duty-cyele modulated input voltage waveform. The L-C Altering funetion ean be approximated by... 

In many instances, the design of suction and discharge pulsation dampening drums (or bottles) for reciprocating compressors is based on piston displacement and volumetric efficiency, and this design normally will suffice to reduce peak pulsation to approximately 5% of the line pressure. In special or other cases, experience has shown that operational difficulties (vibrations, meter pulsations, etc.) may indicate that the peak pulse pressure of 5% line pressure is inadequate. Thus, the pressure in pulsation-reduction design selection is... 

Figure 6. Schematics of the three common regenerative cryocoolers. The Stirling eryocooler (a) uses a valveless compressor or pressure oscillator and has a moving displacer operating synchronously with the piston. The pulse tube eryocooler (b) has no displacer in the cold head. The Gifford-McMahon eryocooler (c) uses a valved compressor with oil lubrication and oil removal equipment.

A discernible trend in modem pump design is towards the use of very small pistons (stroke volume around 100 pi). These tiny pistons have to be operated at very high driving speeds, to provide the flow rates required in analytical HPLC. However, when they are used in combination with electronic feedback pulse control mechanisms, as described above, they can provide extremely stable solvent delivery characteristics. Such is the efficacy of this approach that single piston pumps designed in this way are able to easily out-perform older dual piston pumps, and are consequently beginning to account for a major part of the LC pump market. 

These pumps can be designed with or without a diaphragm. Their operation involves the same mechanism as a cam-drive piston pump, but the movements of the piston are achieved by passing (or not) an electric current through a coiled resistor around the piston [29]. As the solenoid-driven displacement is very abrupt, the pump delivers a pulsed flow [30]. 

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