Hewlett-packard Company

Alan C Herman

Joel Myerson

Andrew Stefanski

H Bryan Bente

Benjamin G Shaw

A plurality of different liquid solutions are connected to an input of a pump system having at least two displacement chambers and in a manner to control the proportions of each constituent that are taken into each chamber during its intake stroke. The outputs of the chambers are connected to a common liquid output. The chambers are driven by independently controllable motors so that the discharge stroke may be chosen to have some parameters, such as speed profile and duration, that are different than during the intake stroke. As a result, both chambers may simultaneously discharge liquid through the common output, if desired. The proportion of constituents may be made different each time one of the chambers is filled, so the simultaneous discharge of the chambers allows a gradual, carefully controlled change from the mixture of one chamber to that of the other. Thus, the pump system can be operated to provide a combination of low pressure and high pressure mixing of two or more liquid constituents in order to provide a smooth gradient in the output liquid flow. Output liquid flow rate can be controlled by changing the time in which the chamber's volume is reduced, or by controlling the maximum volume of the chamber's displacement, or both. Such a pumping system is especially useful in providing a solvent mixture with a gradually changing composition to a liquid chromatograph column.

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Half Moon Bay, CA, United States of America

Alan C Herman