Sinusoidal drive reciprocating pumps

As seen above, the flow of sinusoidal drive reciprocating pumps is greatly pulsed. Even when a triplex pump is used, a residual pulsation remains (Fig. 9b). Most detectors in general use, especially differential refractoineters, are flow sensitive, the pulses increasing the baseline noise, resulting in a poorer detection limit. Under certain conditions, the pulses can even affect the profile of the eluted peaks and thus the resolution, as the HETP is not a linear function of the actual flow-rate. For these reasons, pulse damping is often necessary. 

With the drive mechanism used in a simple reciprocating pump, the profile of the piston position is sinusoidal. Hence the flow-rate profile, which is the first derivative of the piston position profile, provided that the back-pressure is nearly atmospheric, will be half sinusoidal, as shown in Fig, 9a, It can be seen that the flow delivered by a single head is basically pulsed, as the delivery occurs only during the forward stroke. The maximum flow-rate is 3.14 times the average flow-rate. 

Fig. 8. Gradient system using a dual-head sinusoidal-drive counter-piston diaphragm reciprocating pump, a, a = containers of solvents A and B, b, b, = pump heads, c = pump motor, d, d = variable-speed or stepping motor to adjust the course of the counter-piston, e, e = pulse damping systems and flow-rate sensors, f = mixing chamber, g = to column, h = programmer.

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