Hydraulic amplifier pumps

Basically, hydraulic amplifier pumps are similar to pneumatic amplifier pumps as they contain a low-pressure, high-surface-area piston rigidly connected to a high-pressure, low-surface-area piston which deliver the solvent to the column. 

The difference is that they use a low-pressure fluid (oil) instead of a gas. 

The only commercially available hydraulic amplifier pump is the Microiiieritics Model 7000 pump, which is briefly described below (see Fig. 10). 

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, 

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Depending on the principle of operation, we shall distinguish four categories of pumps pneumatic pumps, syringe-type pumps, reciprocating pumps and hydraulic amplifier pumps. The principles of operation of these four types are different and will be described briefly. 

Gradients generated with a hydraulic amplifier pump ... 

Gerhardt, G.C. Compton, B.J. Hydraulic amplifier pumps for use in ultrahigh pressure liquid chromatography. U.S. Patent 6,712, 587 B2, April 30, 2004. 

Pump characteristic Simple single- head Single- head smooth pulse Simple dual-head Dual-head, compressibility-corrected, smooth pulse Dual-head, closed loop flow control Triple head low-volume Syringe- type Hydraulic amplifier Simple Amplifier Amplifier with flow control... 

Jet-cutting systems need to be compact and suitable for robotic action in automated trains of production. Usually the hyper-pressure plunger pumps for water-jet cutting purposes are based on hydraulic amplifiers, of double-cylinder design, and provide high pressure water of up to 5000 bar. 

It is impossible, however, to carry out column recycle chromatography even with pneumatic amplifier pumps because the compounds partially separated would be re-mixed in the hydraulic chamber. Here recycle operation must be understood... 

Another approach to generate ultra-high pressures is to use a conventional HPLC pump with a hydraulic amplifier (see Fig. 9). The differential area provided by the difference in the diameters of the pistons creates a pressure amplification that is proportional to the ratio of the areas. Specifically, the pressure amplification can be calculated as follows ... 

The EOF-induced flow has been amplified by using multiple capillary channels (of width 1-6 pm), so that the multiple flow streams are combined to produce adequate hydraulic pressure for liquid pumping (see Figure 3.7) [115]. The multiple channels (100) ensure the generation of sufficient flow rate (10-400 nL/min), while the small dimensions (of depth 1-6 pm) result in the necessary hydraulic pressure to prevent pressurized backflow leakage (up to 80 psi) [115]. Based on a similar approach, a narrow-gap EOF pump was constmcted to produce 400 Pa pressure with 850-nm-deep channels cascaded in three stages to produce a 200-pm/s flow velocity [390]. Another pump was constructed with 130-nm-thin channels cascaded in 10 stages to produce 25 kPa pressure [264]. 

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