Radial gates have been used for decades primarily because they require about the same force to move them in the closed position against a maximum head pressure or in the nearly full open position, albeit that this raising force is often large enough to require powerful motors.
They traditionally offer only one mode of operation.
The flow goes under the gate as orifice flow and into one of three environments, namely, free-flow, transitional-range-flow, or submerged-flow.
Attempting to accurately measure with these gates has met with limited success.
The lip seals are variable; many of the flows are in the transitional zone that responds poorly to accurate computational procedures, and provision for useful weir flow is not available.
RSA Environmental, INC's Adler Automated Metering Gate addresses many of these concerns by raising the gate mounting blocks, which then allows the gate to rotate though the bottom so that it can operate as an overflow weir as well as in the traditional underflow mode.
The bottom seal is removed from the traditional radial gate edge and is attached to the floor and the side seals are mounted on the channel walls.
The gate bottom is rounded with a half-pipe in an attempt to standardize the exit jet in the hopes of improving and simplifying its hydraulic behavior.
The weir blade is hinged to the gate top so it can rotate and remain vertical regardless of gate opening.
The entire gate is counter weighted to minimize the motor-size requirements.
Previous radial gates depended on the gate weight to close, and usually used cables for opening.
Because of the weir flow requirement, and the counterweights, positive drive to both open and close the gate is needed and is provided with gear drives or linear actuators, depending on size.
The overshot and undershot options, allow the operation of the gate so that the troublesome transition zone can usually be circumvented, particularly when two or more gates are installed across the canal.
The modifications to both the top and bottom of the gate should provide an estimated improvement in measurement accuracy to ±2 %, in the weir mode, and ± 4 %, in the orifice, or undershot, mode.
Sets of multiple adjacent mounted gates with the gate's overshot or undershot features offer canal operators new and useful capabilities to maintain upstream water levels that can pass both bottom and floating debris when using the weir to pass top flow and the undershot mode to pass bottom sediments, while sending controlled volumes of accurately measured flow downstream.
