Ion Chromatography - Pumps

Pumps

There are a number of different types of high pressure liquid chromatography pumps that have been developed over the years (single piston pumps, dual piston pumps, rapid refill pumps etc.) but it is not appropriate to describe them all in this book. The most common, and least expensive pump that is manufactured is the single piston high pressure pump (that gives a basic understanding of how pumps in general are constructed) a diagram of which is shown in figure 13.

The single-piston reciprocating pump was the first of its type to be used with high efficiency LC columns (columns packed with small particles) and is still very popular today. Most pistons of modern LC pumps are made of synthetic sapphire to reduce wear and extend the working life of the pump. The cylinder is usually made of stainless steel (but in the case of pumps used for ion exchange chromatography may be made from some suitable inert material) and is attached to two non-return valves in line with the inlet and outlet connections to the pump. Most pistons of modern LC pumps are made of synthetic sapphire to reduce wear and extend the working life of the pump. The cylinder is usually made of stainless steel (but in the case of pumps used for ion exchange chromatography may be made from some suitable inert material) and is attached to two non-return valves in line with the inlet and outlet connections to the pump.

Figure 13. The Single Piston High Pressure Reciprocating Pump

The piston is driven by a stainless steel cam, which forces the piston into the cylinder expressing the solvent through the exit non-return valve. After reaching the maximum movement, the piston follows the cam and returns as a result of the pressure exerted by the return spring. During this movement the cylinder is loaded with more solvent through the inlet non-return valve. The shape of the cam is cut to provide a linear movement of the piston during expression of the solvent but a sudden return movement on the refill stroke. In this way the pulse effect that results from the refill action is reduced. The pulses, however, are not completely eliminated and the detector noise resulting from these pulses is probably the most serious disadvantage of the single piston pump. Nevertheless, as a result of its low cost it remains one of the more popular LC pumps.