A variable orifice valve for a storm water management system of the type that discharges water into a discharge pipe, stores the excess storm water in a storage chamber, and is responsive to movement of a float floating in the storage chamber caused by changes in water level of the water stored in the storage chamber to vary the discharge rate from the system as a function of water level, the valve comprising:
- a valve body having an intake opening that receives water into the valve and a discharge opening that discharges water from the valve, and further comprising a movable valving member, a fixed valving member, and a transmission connectable to the float and the moveable valving member;
- the movable valving member being movable with respect to the fixed valving member through a range of motion;
- the transmission when connected to the float and to the moveable valving member converting movement of the float to the relative movement of the movable valving member;
- one of the valving members being an outer valving member of the valve and comprising a tubular body defining a hollow interior of the tubular body, the tubular body comprising a wall surrounding the interior of the tubular body, the wall comprising an outer surface and an inner surface being separated from the outer surface by a thickness of the wall, the outer surface being an outer surface of the valve and the inner surface facing the interior of the tubular body;
- the outer valving member further comprising a first through-hole and a second through-hole, the first through-hole spaced from the second through-hole, each of the first and second through-holes extending through the thickness of the wall and being disposed to fluidly communicate the interior volume of the storage chamber with the exterior of tubular body whereby one of the first and second through-holes forms the intake opening of the valve and the other of the first and second through-holes forms the discharge opening of the valve;
- the other valving member being an inner valving member of the valve, the inner valving member being at least partially disposed in the interior of the outer valving member, the inner valving member being adjacent to and facing the inner surface of the outer valving member, the inner valving member being movable with respect to the outer valving member along the inner surface of the outer valving member during relative movement of the movable valving member with respect to the fixed valving member;
- the inner valving member comprising a through-hole extending through the inner valving member and being disposed to receive water into the inner valving member and to discharge water out of the inner valving member, the through-hole of the inner valving member being disposed in series with the first and second through-holes of the outer valving member whereby water flowing into the intake opening of the valve flows through the inner valving member before being discharged from the discharge opening of the valve;
- an end of one of the first and second ends of the outer valving member facing an end of the through-hole of the inner valving member, each end having a respective flow area, the facing ends cooperatively defining a variable-flow orifice formed from said facing ends, the facing ends overlapping one another during relative movement of the inner and outer valving members to enable water to flow through the variable-flow orifice;
- the facing ends each of the variable flow orifice defining a flow area of the variable flow orifice, the flow area of the variable flow orifice being the net flow area defined by the facing ends, the flow area of the variable orifice varying with relative movement of the movable valving member along at least a portion of the range of motion of the movable valving member.