Pumps pressure intensifier

Fig. 4.1-14. Double-head high-pressure intensifier metering pump.

Constant pressure pumps utilise pneumatics or hydraulics apply the pressure required to force the mobile phase through the column, either directly or indirectly. Two main designs of constant pressure pump exist the pressurised coil pump, and the pneumatic pressure intensifier type. The pressurised coil pump is now all but redundant, but as it represents the most simple means possible of pumping at high pressure through an HPLC column it is described briefly. 

Pressure intensifier pumps. The most common examples are pneumatic in principle, although hydraulic versions have been described. 

Fig. 8.151 Photograph and schematic (inset) of a modern high pressure intensifier pump (courtesy EPSI, Haverhili, MA. USA).

Fig. 6.7-29 Photograph and diagram of a dry-bag CIP system (courtesy Dorst, Kochel am See, Germany). 1, protective enclosure 2, control cabinet 3, hydraulic unit 4, high-pressure intensifier pump 5, loading device 6, hopper 7, dosing device ...

Other problems with pneumatic intensifier pumps include the fact that access to the high pressure seals for inspection and maintenance is usually quite restricted, by nature of their design. Because of the way they operate, the flow they produce is inherently highly pulsatile in nature and they also tend to be extremely noisy in use. For these reasons, pumps of this type are not used in general analytical HPLC. However, pneumatic intensifier pumps have found a niche in the packing of HPLC columns, where the intermittent nature of the function and their ability to deliver very high pressures compensate somewhat for their shortcomings in the analytical field. 

In all cases, the pressure used should be the lowest which will do the work. This saves first cost, power and time. In many instances a part of an operation can be performed at low pressure, the finish only requiring high pressure. This dual system may be provided by a complete duplication of pumps, accumulators and piping, with manual or automatic transfer valves, or intensifiers may be used at points of fluid consumption. These are pumps using the low-pressure fluid as the actuating medium in what corresponds to the steam cylinder, to produce a local excess pressure. 

Autoclaves, high-pressure optical cells, valves, pumps, gauges, fittings, and intensifiers to 7 kbar... 

Fig. 10. Hydraulic fluid-solvent pumping and distribution systems. Black, tubes pressurized liquid. Hatched tubes alternate, a = oil reservoir, b = gear pump, c = pressure limiter, d = bleed check, e = low-pressure accumulator, f = intersifier (1,2,3,4), g = solenoid valves A,B,C,D), h = blending valve, i = pressure transducer, j = mixing chamber, k = to column, 1 = weak solvent, m = strong solvent. Courtesy Micromeritics Instrument Co. Since completion of the manuscript we have been aware of a change In the method for proportioning mobile phase. Now Micromeritics Model 7000 B uses an additional pair of solenoids to blend mobile phase by proportioning the application of hydraulic fluid on the low pressure side of the hydraulic intensifiers.

To understand the basic cycle of the pump, let us imagine that there is only the weak solvent line (the pump is used to generate a gradient), that the outlet lines of intensifiers Mos. 1 and 2 are connected before the pressure transducer, and ignore the intensifiers Nos. 3 and 4, the blending valve and the mixing chamber. 

When the active intensifier is almost empty, the pressure is recorded in a memory device and the second intensifier begins to pump. The two intensifiers then pump together and the gear-pump speed is controlled so as to keep the pressure constant at the recorded value, irrespective of the selected mode set on the front panel. Then, the empty intensifier is switched off, set in the re-fill position and standard working conditions are resumed. A bleed check valve serves to re-fill the accumulator smoothly. This system avoids the pressure fall which would otherwise follow connutation from one intensifier to the other,... 

FM = flow meter I = intensifier LCV = liquid collection vessel LP = liquid pump P = pressure transducer PCV = pressure control valve RV = relief valve ... 

An overstepping of the presetting produces a back pressure of the liquid in the vacuum pump. This leads to an increase in the internal compression ratios and therewith also to the increase in the power consumption. The results can be an overloading of the components as well as an intensified noise development by flow separations. 

In order to obtain water under high pressure suitable for industrial waterjet cutting, the hydraulic intensifier pump or mechanical directly driven (electric or diesel motor) plunger pumps are used. 

---