Pulse dampers

Most high-performance liquid chromatography (HPLC) pumps can be used in HOPC. The back pressure rating should be at least several thousand pounds per square inch (a few hundred kg/cm ). A type of pump that does not allow bypassing the pressure transducer or a pulse damper, if it is installed, must not be used. The dead volume should be as small as possible. Pumps with a single plunger are better than those with two plungers. 

The truly parallel approach of this technology permits many different samples to be separated simultaneously using a minimum number of common system components such as pumps and pulse dampers. To increase the automation of the system, a plate loader and exchanger that accommodate... 

The pumping rate is controlled by piston retracts or by the cam rotating speed. The main drawback of this type of pump is sinusoidal pressure pulsations which lead to the necessity of using pulse dampers. 

The Micromeritics 7000 liquid chromatograph (Fig.3.30) also uses a reciprocating pumping system. The pump has several unique features. It delivers pulseless flow without a pulse damper, it can operate from an unlimited reservoir, it requires only a single pump for gradient elution and it is capable of operating at constant pressure or constant flow-rate. 

Figure 3.5 Reciprocating-piston pump head showing the check valves, piston, seal, and pulse damper. (Adapted from Ref. 1 with permission.)...

This analysis is performed using a Dionex Model 12 ion chromatograph with 200pL sample loop, an eluent flow rate of 2.3ml min 1 (30% of full capacity) and a sample pump flow rate of 3.8ml min 1 (50% of full capacity). Pulse damper is installed just before the injection valve to reduce flow pulsation. A Dionex amperometric detector... 

Constant flow reciprocating pumps are now the most widely used type (figure 4.26a), but because their mechanical action inherently produces a pulsating delivery of the mobile phase the flow must be smoothed so as to eliminate the pulsations. This can be achieved in several ways, the simplest being the incorporation of a pulse damper in the flow to the column. One... 

The general arrangement of an hplc system is fairly simple, as shown in Fig. 9.17. Solvent is pumped from a reservoir through a piston pump which controls the flow rate. From the pump the solvent passes through a pulse damper which removes some of the pulsing effect generated in the pump and also acts as a pressure regulator. In between the pulse damper and the column there is an injection valve which allows the sample to be introduced into the solvent stream. 

Periodic-pump pulses Service or replace pulse damper purge air from pump clean or replace check valves. 

Pulse damper failure Replace pulse damper. 

Where a single-stage pump is used, it is common to find that pressure fluctuations occur in the ceU, causing serious "noise" in the detector signal. An additional pulse damper working on the Bourdon tube principle can assist in minimising "noise" from this source. 

Figure 8. Schematic of typical apparatus for SEC 1, mobile-phase reservoir 2, solvent metering pump 3, pressure gauge 4 and 5, pulse damper 6, thermostat 7, sample injection valve 8, SEC chromatographic columns 9, detector 10, recorder and 11, computer.

Fig. 20. Block diagram of HPLC column switching system with electrochemical detection. L, sample loop 7125 and 7010, injection valves W, waste PC, precolumn AC, analytical column AMP, electrochemical detector REC, strip chart recorder PD, pulse dampers PS, presaturator columns.

A typical block scheme of gel chromatographic apparatus is shown in Fig. 4.6.4. The mobile phase flows from the solvent container, C, into degassing unit, D, and through filters, F, reaches the pumping system, P, which transports it via the pulse damper, PD, and the sample injecting system, I, into the column, CO. The effluent from the column enters the detector, DE, and flows through the volumeter, V, into the fraction collector, F. 

Twd types of pulse dampers using a controlled gas pressure and a leak have been described one uses a diaphragm to separate the gas and the liquid compart ments and to control the opening of the leak, and the other uses a tee-assembly Such devices act as pressure regulators, and therefore can be considered as pneumatic pumps with unlimited capacity. 

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