A device for use in a dilution system, the device comprising: a first component comprising a metering disc (116, 216, 316, 416, 516, 616, 716, 816), the metering disc (116, 216, 316, 416, 516, 616, 716, 816) defining a metering groove (144, 244, 344, 444, 844) having an inlet portion (150, 250, 350, 450, 850) and an outlet portion (152, 252, 352, 452, 852), the metering groove (144, 244, 344, 444, 844) formed in a surface (142, 842) of the metering disc (116, 216, 316, 416, 516, 616, 716, 816); and a second component comprising a first housing component (106, 806) coupled with a second housing component (108, 808), wherein the first housing component (106, 806) functions as a cover for the second housing component (108, 808), wherein the metering disc (116, 216, 316, 416, 516, 616, 716, 816) is received in a cavity (118, 818) of the second housing component (108, 808) and is covered by the first housing component (106, 806) such that the second component encloses the first component therein, the second housing component (108, 808) defining an inlet in fluid communication with the inlet portion (150, 250, 350, 450, 850) of the first component and an outlet in fluid communication with the outlet portion (152, 252, 352, 452, 852) of the first component, the inlet and outlet each comprising a through-hole extending through the second housing component (108, 808) from an interior to an exterior of the second component; characterized in that: relative rotation between the first component and the second component causes relative movement between the outlet and the outlet portion (152, 252, 352, 452, 852) that changes an effective length of the metering groove (144, 244, 344, 444, 844) fluidly coupling the inlet and the outlet of the second component; and the cross-sectional area of the metering groove (144, 244, 344, 444, 844) varies along a length of the metering groove (144, 244, 344, 444, 844) to provide different flow restriction depending on the effective length of the metering groove (144, 244, 344, 444, 844). a first component comprising a metering disc (116, 216, 316, 416, 516, 616, 716, 816), the metering disc (116, 216, 316, 416, 516, 616, 716, 816) defining a metering groove (144, 244, 344, 444, 844) having an inlet portion (150, 250, 350, 450, 850) and an outlet portion (152, 252, 352, 452, 852), the metering groove (144, 244, 344, 444, 844) formed in a surface (142, 842) of the metering disc (116, 216, 316, 416, 516, 616, 716, 816); and a second component comprising a first housing component (106, 806) coupled with a second housing component (108, 808), wherein the first housing component (106, 806) functions as a cover for the second housing component (108, 808), wherein the metering disc (116, 216, 316, 416, 516, 616, 716, 816) is received in a cavity (118, 818) of the second housing component (108, 808) and is covered by the first housing component (106, 806) such that the second component encloses the first component therein, the second housing component (108, 808) defining an inlet in fluid communication with the inlet portion (150, 250, 350, 450, 850) of the first component and an outlet in fluid communication with the outlet portion (152, 252, 352, 452, 852) of the first component, the inlet and outlet each comprising a through-hole extending through the second housing component (108, 808) from an interior to an exterior of the second component; characterized in that: relative rotation between the first component and the second component causes relative movement between the outlet and the outlet portion (152, 252, 352, 452, 852) that changes an effective length of the metering groove (144, 244, 344, 444, 844) fluidly coupling the inlet and the outlet of the second component; and the cross-sectional area of the metering groove (144, 244, 344, 444, 844) varies along a length of the metering groove (144, 244, 344, 444, 844) to provide different flow restriction depending on the effective length of the metering groove (144, 244, 344, 444, 844). relative rotation between the first component and the second component causes relative movement between the outlet and the outlet portion (152, 252, 352, 452, 852) that changes an effective length of the metering groove (144, 244, 344, 444, 844) fluidly coupling the inlet and the outlet of the second component; and the cross-sectional area of the metering groove (144, 244, 344, 444, 844) varies along a length of the metering groove (144, 244, 344, 444, 844) to provide different flow restriction depending on the effective length of the metering groove (144, 244, 344, 444, 844).