Piston pump, advantages

The use of traditional rod and piston pumps continues at many LNAPL recovery locations, particularly at refineries and distribution terminals. These units are usually powered by single-speed electric motors and have adjustable stroke lengths to control the pumping rate. When installed with the intakes set at the optimum pumping depth, they function fairly well. The primary advantage of rod and piston pumps is that the smooth slow stroke rate can pump mixtures of product and water without creating a significant emulsion. 

To form a pendant drop, the gear pump (2) was switched off and the air driven oscillating double piston pump (4) with 1.8 ml per stroke was used. This pump has the advantage of keeping the volume constant in the apparatus while pumping. The drop size was controlled by closing the metering valve (5). 

The same detector system can be used in FIA work, although it is obvious that, without the use of an HPLC column, separation of compounds with similar electrode discharge potentials will not be possible. The FIA system does however have advantages over straight-forward voltammetry in that the volumes required for injection are of the same order as they are in HPLC work. The pump requirements are often simpler, and a motor-driven piston pump is very often adequate for precise and accurate work. 

Reciprocating pumps are versatile and widely used. They consist of a small cylindrical chamber that is fdled and then emptied by the back-and-forth motion of a piston. Advantages include small internal volume, high output pressures, adaptability to gradient elution, and constant flow rates that are independent of viscosity and back pressure. The pulsed output must be damped. 

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