Dual-piston reciprocating pump

Figure 6-15 Cross-sectional view of a dual-piston reciprocating pump. (From Walker JQ, Jackson MT Jr, Maynard JB Chromatographic systems Maintenance and troubleshooting, 2nd edition, New York Academic Press. 1977.)...

Figure 6.8 Single-cam dual piston reciprocating pump.

The most important parts of the instruments are the pumps for maintaining constant, pulseless rates of flow, the column types for the molecular weight range of analysis, and the detector system see Table 3.12. Some of the popular types of solvent delivery pumps include syringe pumps, the plunger of which is actuated by a screw-fed stepper motor, and the dual piston reciprocating pumps, which may have the pistons in either series or parallel see Figure 3.19 (79). 

Table 1. List ot modern HPLC dual piston reciprocating pump operating specifications.

Dual-head reciprocating pumps offer lower solvent pulsation at the expense of mechanical complexity. Here two pistons fill and pump 180° out of phase and in theory provide pulseless flow. Dual-head pumps are more expensive and have either two check valves (series heads) or four check valves (parallel heads). Both designs generally provide for some type of pressure or flow feedback control to further compensate for minor flow variations during switching from one head to the next. A detailed discussion of the mechanics of these and other pumping systems is provided elsewhere (13). 

In order to damp almost completely the pulses generated at high pressure in a dual-head, special-drive piston reciprocating pump, the electronic correction circuitry in the Altex Model 100 pump calculates the average back-pressure and then corrects the speed of the pump motor so as to maintain the actual pressure close to the average calculated pressure. The effect of this correction is to speed up the motor momentarily when pumping is switched from one piston to the... 

Reciprocating pumps are those most commonly used in high performance Ic. The single-piston type usually has inlet and outlet check valves with some mechanism such as variable stroke frequency to minimize the effect of pump pulsations. Dual-piston pumps operate with the pistons 180° out of phase to minimize pulsations. For this system to work optimally, the piston units must be identical. 

Reciprocating Pumps—Single- and dual-headed pumps that use a piston and check valves to pump solvent from a reservoir into the system. 

Figure 3.6 Cam-driven, dual-head reciprocating-piston pump capable of delivering constant flow with relatively low pulsation. Flow rate is controlled by the cam rotation frequency. (Reprinted from Ref. 3 with permission.)...

Figure 19-17. A dual piston two-cam reciprocating pump. (Courtesy - R. Macrae, HPLC in Food Analysis, Academic Press, London, 1982)...

Fig, 9. Piston position and flow in reciprocating pomps. In each figure the upper curve gives the position of the piston and the lower curve the flow-rate profile as a function of time, (a) Single sinusoidal piston movement head A = backward stroke, B = forward stroke, (b) Three sinusoidal piston movement heads. In the lower diagram the thick solid line indicates the total flow-rate, (c) Dual-head, special-piston movement pump. 1 piston A accelerates 2 piston A moves at constant speed 3 piston A decelerates 4 piston A retracts 1 to 4 similar movements of piston B. The broken line indicates the total 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.

Type of pump dual piston dual bead reciprocating reciprocating diaphragm reciprocating pneumatic amplifier pneumatic amplifier syringe dual head reciprocating... 

A reliable high pressure liquid pumping system (generally reciprocating-dual piston design to avoid pressure fluctuations) is one of the most important parts of SEC. Since SEC calibration is based on the retention time in the columns and the logarithm of the molecular weight varies very often as a linear function... 

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