Reciprocating piston pumps

Vacuum pumps reciprocating piston type decrease the pressure to 1 Torr rotary piston down to 0.001 Torr, two-iobe rotary down to 0.0001 Torr steam jet ejectors, one stage down to 100 Torr, three stage down to 1 Torr, five stage down to 0.05 Torr. 

Constant-flow systems are generally of two basic types reciprocating piston and positive displacement (syringe) pumps. Reciprocating piston pump can maintain a liquid flow for indefinitely long time. 

Type of pump Reciprocating, piston-type metering pump... 

From the last shown elution method, it is clear that the pump is a very important accessory for high-pressure liquid chromatography. There are three main types of pumps used in modern chromatographs membrane pumps reciprocating piston pumps syringe type pumps constant pressure pumps... 

The flow of the SCF under pressure is maintained by long-stroke piston pumps, reciprocating piston pumps, or membrane pumps which deliver the mobile phase in liquefied form. The fluid is then heated to supercritical conditions before entering the column. Pressure and flow rate must be kept as constant as possible in order to maintain constant conditions for separation and to achieve a stable baseline in the chromatogram. Oscillating pumps can therefore have three heads, which deliver at different times, or a pulsation dampener in order to minimize pulsation. 

The delivery system can either be a syringe pump, reciprocating piston pump, or gas compressor. Both syringe and reciprocating piston pumps are available on analytical-scale commercial instrumentation. These are used for analytical-scale extractions, while gas compressors are typically used for large-scale... 

There are several important calculations that are needed in order to properly evaluate and select the appropriate reciprocating piston pump [17]. These calculations are used in conjunction with Equations 3-32-3-37. 

In much the same manner as pumps, compressors are classified as one of two general classes positive displacement or dynamic (see Figure 3-68) [23]. These two general classes of compressors are the same as that for pumps. The positive displacement class of compressors is an intermittent flow device, which is usually a reciprocating piston compressor or a rotary compressor (e.g., sliding vane, screws, etc.). The dynamic class of compressor is a continuous flow device, which is usually an axial-flow or centrifugal compressor (or mix of the two). 

Positive-displacement pumps can be divided into two major types rotary and reciprocating. All rotary pumps use some form of rotating element, such as gears, vanes, or lobes to increase the discharge pressure. Reciprocating pumps use pistons or wobble plates to increase the pressure. 

SINGLE - ACTING RECIPROCATING PISTON PUMP --[fixed speed - AD2U S ABL E S1LR0KE L E GT h]... 

A central component of the LC instrument is the pump, for its characteristics can strongly influence an analysis (e.g., flow reproducibility). The three principal types of systems— pneumatic, syringe type and reciprocating piston—have been reviewed in the literature (18-20). 

Reciprocating-piston pumps deliver a constant flow at si fixed backpressure. At high pressures some minor flow variability ziay arise due to the compressibility of the mobile phase. Soms instruments incorporate a flow controller which provides a fixadi backpressure for the pump to work against, independent of the column backpressure. The influence of pressure fluctuations, solvent compressibility, and solvent viscosity on the volumetrie output of the pump are thereby eliminated. Reciprocating-piston pumps can provide continuous solvent delivery, fast solvent change--... 

The piston is driven in and out of a solvent chamber by an eccentric cam or gear. On the forward stroke, the inlet check valve closes, the outlet valve opens, and mobile phase is pumped to the column on the return stroke the outlet valve closes and the chamber is refilled. Unlike syringe pumps, reciprocating pumps have an unlimited capacity, and their internal volume can be made very small, from 10-100 p. The flow rate can be varied by changing the length of stroke of the piston or the speed of the motor. Access to the valves and seals is usually fairly straightforward. 

FIGURE 13.4 An illustration of a reciprocating piston pump with check valves. Left, the piston is in its upstroke, drawing mobile phase in from the reservoir. Right, the piston is in its downstroke, pushing mobile phase out to the column. 

Describe what is meant by a reciprocating piston pump. 

A reciprocating piston pump is a pump that utilizes a piston in a cylinder to pull and push the liquid mobile phase from the mobile phase reservoir through the HPLC system. Two check valves (backflow preventers) are in-line to help force the liquid in only one direction. See Figure 13.4. 

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