Pneumatic pump The pneumatic pump is double piston pump, one piston having a relatively large diameter and the other a relatively small diameter. The two pistons are connected together and fit inside two connected cylinders. The smaller cylinder is fitted with inlet and outlet non-return valves. The larger piston is driven by compressed air(the gas alternately driving the piston in one direction and then the other) and actuates the smaller piston which pumps the liquid. The system acts as a pressure amplifier, as the output pressure from the pump with the smaller piston will be equal to the pressure applied to the larger piston times the ratio of the cross-sectional area of the larger piston to that of the smaller piston. This type of piston was originally used for normal liquid chromatography separations but was found to be noisy and produced strong flow pulses that destabilized the detector. It is now used almost exclusively for slurry packing liquid chromatography columns. It is the simplest type of pump that can be designed to provide exceedingly high pressures.

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Author: RPW Scott Book:Liquid Chromatography
Section:HPLC   Basic-HPLC   Pump   Pneumatic

common use; they were the pneumatic pump, where the necessary high pressures were achieved by pneumatic amplification, and the syringe pump, which was simply a large, strongly constructed syringe with a plunger that was driven by a motor. Today the majority of modern chromatographs are fitted with reciprocating pumps fitted with either pistons or diaphragms. For more information on HPLC pump requirements see the pump section in the HPLC supplement. The Pneumatic Pump The pneumatic pump has a much larger flow capacity than the piston type pumps but, nowadays, is largely used for column packing and not for general analysis. The pneumatic pump can provide extremely high pressures and is relatively inexpensive, but the high pressure models are a little cumbersome and, at high flow rates, can consume considerable quantities of compressed air. A diagram of a pneumatic pump is shown in figure 4. Figure 4. A Diagram of the Pneumatic Pump

HPLC   Basic-HPLC   Pump   Pneumatic