Linear piston pump

Linear-piston pump. The third type of pump used in dispensers, linear piston, is a true positive-displacement pump. This pump uses a piston to change the volume of a reservoir that is fed from the main syringe. The displacement of the piston produces an equivalent positive displacement of fluid through the pump. Changes in viscosity have little or no effect on the repeatability of dispensedmass. Ofthethreemethods, the repeatability ofthe linear-piston type is the best ( 1 %, except for very small dispense volumes of less than 20 microliters), Repeatability of the time-pressure method is... 

Rotary piston vacuum pumps are based on the rotational action of an eccentric cam — not a piston producing a reciprocating action in a linear direction. Like linear piston pumps, it is the piston in this pump which is exposed to the material being removed from the work chamber. 

A wide variety and numerous suppliers of automated dispensing equipment are available as listed in Table 4.22. An important consideration in selecting an automated, contact-type dispensing system is the pump used in the system, of which there are three types time-pressure, auger, and linear piston or positive displacement. " ... 

Another pump, the Evolution 200, can also deliver low flow rates with high precision, with isocratic flows down to 0.1 pi min and gradient flows from Iplmin. This system uses binary high-pressure gradient formation with two linear drive piston pumps. 

In order to obtain very low flow rates without pulsation (e.g. 1 pl/min), pumps based on the principle of high volume motorised syringes are used. The piston, activated by a pneumatic amplifier, moves at a constant linear velocity. These pumps are still in widespread use. 

The outlet flow-rate of one pump head depends on the length of travel of the piston and its cycle frequency, and also on the back-pressure. Indeed, solvent delivery occurs during the forward piston stroke only when the column check valve opens, that is, when the pressure in the solvent chamber becomes equal to the back-pressure. As the pressure in the solvent chamber is atmospheric at the end of the backward stroke and because of the compressibility of liquids (about 10 /atm for most chromatographic solvents) and the elasticity of the chamber, part of the forward stroke of the piston serves to compress the liquid in the solvent chamber before delivery against the back-pressure. Hence the outlet fTow--rate decreases nearly linearly when the outlet back-pressure increases. The importance of this phenomenon increases with increasing chamber volume and liquid... 

The compressor is a device that increases the pressure of air and pumps the compressed air into a tank. The compressed air tank is called a reservoir. The compressed air is then routed to the desired location through transmission lines. Transmission lines are tubing through which the compressed air flows. Control valves regulate the flow of gases. The pneumatic system uses a cylinder with a movable piston to convert its fluid power into mechanical power in the form of linear motion. 

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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