Hybrid gradient delivery system and operation

A solvent delivery system for use in a liquid chromatography system, comprising:

• a first gradient proportioning valve in fluidic communication with a first plurality of sources of solvent and producing therefrom a first low-pressure gradient stream;
• a first pump in direct fluidic communication with the first gradient proportioning valve to receive and pressurize the first low-pressure gradient stream and to move the first pressurized low-pressure gradient stream to a flow-combining device;
• a second pump operating in parallel with the first pump, the second pump moving a pressurized solvent stream to the flow-combining device where the pressurized solvent stream combines with the first pressurized low-pressure gradient stream to produce a high-pressure gradient stream;
• a second gradient proportioning valve in direct fluidic communication with an inlet of the first gradient proportioning valve and with a second plurality of sources of solvent, the second gradient proportioning valve producing a second low-pressure gradient stream from the second plurality of sources of solvent, wherein one solvent source of the first plurality of sources of solvent used by the first gradient proportioning valve to produce the first low-pressure gradient stream comprises the second low-pressure gradient stream;
• and
• a third gradient proportioning valve in fluidic communication with a third plurality of sources of solvent and producing therefrom a third low-pressure gradient stream, and wherein the second pump is in direct fluidic communication with the third gradient proportioning valve to receive and pressurize the third low-pressure gradient stream, wherein the pressurized solvent stream moved by the second pump to the flow-combining device comprises the third low-pressure gradient stream.