A system (100, 300) for mixing deionized water and sheath fluid concentrate comprising: a first container (104, 304) adapted to supply deionized water; a second container (106, 306) adapted to supply concentrated sheath fluid; a pressurized reservoir (102, 302); a valve (112, 312) that has: a first input (108, 308) that is coupled to the first container, a second input (110, 310) that is coupled to the second container, and an output (114, 314) wherein the valve supplies the deionized water through the output to the pressurized reservoir when the valve is in a first position, and supplies the concentrated sheath fluid through the output to the pressurized reservoir when the valve is in a second position; a pump (116, 316) that is interposed between the valve and the pressurized reservoir and that, when operating and depending on the position of the valve, delivers the deionized water or the concentrated sheath fluid into the pressurized reservoir at a rate that is sufficiently slow that no bubbles form in the pressurized reservoir; a controller (122, 322) that places the valve in the first position until a predetermined amount of the deionized water is supplied to the pressurized reservoir, and switches the valve to the second position until a predetermined amount of the concentrated sheath fluid is supplied to the pressurized reservoir, so that the predetermined amount of the deionized water and the predetermined amount of the concentrated sheath fluid maintain a mixture in the pressurized reservoir having a desired concentration of sheath fluid. a first container (104, 304) adapted to supply deionized water; a second container (106, 306) adapted to supply concentrated sheath fluid; a pressurized reservoir (102, 302); a valve (112, 312) that has: a first input (108, 308) that is coupled to the first container, a second input (110, 310) that is coupled to the second container, and an output (114, 314) wherein the valve supplies the deionized water through the output to the pressurized reservoir when the valve is in a first position, and supplies the concentrated sheath fluid through the output to the pressurized reservoir when the valve is in a second position; a pump (116, 316) that is interposed between the valve and the pressurized reservoir and that, when operating and depending on the position of the valve, delivers the deionized water or the concentrated sheath fluid into the pressurized reservoir at a rate that is sufficiently slow that no bubbles form in the pressurized reservoir; a controller (122, 322) that places the valve in the first position until a predetermined amount of the deionized water is supplied to the pressurized reservoir, and switches the valve to the second position until a predetermined amount of the concentrated sheath fluid is supplied to the pressurized reservoir, so that the predetermined amount of the deionized water and the predetermined amount of the concentrated sheath fluid maintain a mixture in the pressurized reservoir having a desired concentration of sheath fluid. a first input (108, 308) that is coupled to the first container, a second input (110, 310) that is coupled to the second container, and an output (114, 314) wherein the valve supplies the deionized water through the output to the pressurized reservoir when the valve is in a first position, and supplies the concentrated sheath fluid through the output to the pressurized reservoir when the valve is in a second position; a pump (116, 316) that is interposed between the valve and the pressurized reservoir and that, when operating and depending on the position of the valve, delivers the deionized water or the concentrated sheath fluid into the pressurized reservoir at a rate that is sufficiently slow that no bubbles form in the pressurized reservoir; a controller (122, 322) that places the valve in the first position until a predetermined amount of the deionized water is supplied to the pressurized reservoir, and switches the valve to the second position until a predetermined amount of the concentrated sheath fluid is supplied to the pressurized reservoir, so that the predetermined amount of the deionized water and the predetermined amount of the concentrated sheath fluid maintain a mixture in the pressurized reservoir having a desired concentration of sheath fluid.