A solvent delivery system for use in a liquid chromatography system, comprising: a first gradient proportioning valve configured for fluidic communication with a first plurality of sources of solvent to produce therefrom a first low-pressure gradient stream; a first pump configured for fluidic communication with the first gradient proportioning valve for receiving and pressurizing the first low-pressure gradient stream and moving the pressurized first low-pressure gradient stream to a flow-combining device; a second pump operable in parallel with the first pump, the second pump for moving a pressurized solvent stream to the flow-combining device where, in use, the pressurized solvent stream combines with the pressurized first low-pressure gradient stream to produce a high-pressure gradient stream; a second gradient proportioning valve configured for fluidic communication with the first gradient proportioning valve and with a second plurality of sources of solvent, the second gradient proportioning valve configured to produce a second low-pressure gradient stream from the second plurality of sources of solvent, wherein, in use, 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 configured for fluidic communication with a third plurality of sources of solvent to produce therefrom a third low-pressure gradient stream, and wherein the second pump is configured for fluidic communication with the third gradient proportioning valve for receiving and pressurizing the third low-pressure gradient stream, wherein, in use, the pressurized solvent stream moved by the second pump to the flow combining device comprises the third low-pressure gradient stream. a first gradient proportioning valve configured for fluidic communication with a first plurality of sources of solvent to produce therefrom a first low-pressure gradient stream; a first pump configured for fluidic communication with the first gradient proportioning valve for receiving and pressurizing the first low-pressure gradient stream and moving the pressurized first low-pressure gradient stream to a flow-combining device; a second pump operable in parallel with the first pump, the second pump for moving a pressurized solvent stream to the flow-combining device where, in use, the pressurized solvent stream combines with the pressurized first low-pressure gradient stream to produce a high-pressure gradient stream; a second gradient proportioning valve configured for fluidic communication with the first gradient proportioning valve and with a second plurality of sources of solvent, the second gradient proportioning valve configured to produce a second low-pressure gradient stream from the second plurality of sources of solvent, wherein, in use, 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 configured for fluidic communication with a third plurality of sources of solvent to produce therefrom a third low-pressure gradient stream, and wherein the second pump is configured for fluidic communication with the third gradient proportioning valve for receiving and pressurizing the third low-pressure gradient stream, wherein, in use, the pressurized solvent stream moved by the second pump to the flow combining device comprises the third low-pressure gradient stream.