Steam-metering method and apparatus

In the method of metering the supply of a fluid over a wide range of demand involving a high-demand line and a low-demand line connected in parallel, wherein each line includes flow-metering means connected to a control valve to govern the transfer of flow to the low-demand line at the low end of the metering range of the high-demand line and to transfer flow to the high-demand line at the upper end of the range of the low-demand line,

• the improvement which comprises
• Step (1), delaying the control of any such transfer for a predetermined interval of sustained change in demand, whereby to avoid response to transient changes in demand;
• Step (2), initiating only after said predetermined interval has run, and
• Step (3), effecting the transfer control by predetermined relatively slow progressive change in at least a valve-opening actuation of said control valves, whereby to avoid rapid change in fluid flow in the line to which flow is being transferred.

In a steam-flow measuring system comprising a high-demand line and a low-demand line connected in parallel between a supply-receiving inlet and a supply-delivering output, a motor-operated flow-control valve and a metering orifice in each of said lines, first and second differential-pressure switches connected across the respective orifices, the first of said differential-pressure switches being operative to change its state upon detection of steam flow at the upper end of the metering range of the low-demand line and the second of said differential-pressure switches being operative to change its state upon detection of steam flow at the lower end of the metering range of the high-demand line, a first resetting delay-timing switch connected for operation by said first differential-pressure switch for timing a first predetermined interval to avoid valve response to a steam-flow transient condition, first controller means responsive to completion of a timed delay by said first delay-timing switch and establishing a valve-opening motor-drive connection to the motor-operated control valve of the high-demand line, and second controller means concurrently responsive to completion of said first interval and establishing a valve-closing motor-drive connection to the motor-operated control valve of the low-demand line, a second resetting delay-timing switch connected for operation by said second differential-pressure switch for timing a second predetermined interval to avoid valve response to a steam-flow transient condition, said first controller means being responsive to completion of a second interval by said second delay-timing switch and establishing a valve-closing motor-drive connection to the motor-operated control valve of the high-demand line, and said second controller means being responsive to completion of said second interval and establishing a valve-opening motor-drive connection to the motor-operated control valve of the low-demand line.

In a fluid-flow measuring system comprising a high-demand line and a low-demand line connected in parallel between a supply-receiving inlet and a supply-delivering output, a motor-operated flow-control valve and a flow-measuring device in each of said lines, the first of said flow-measuring devices being operative to produce an electrical change of state upon detection of fluid flow at the upper end of the metering range of the low-demand line and the second of said flow-measuring devices being operative to produce an electrical change of state upon detection of fluid flow at the lower end of the metering range of the high-demand line, first resetting delay-timing means connected for operation by said first flow-measuring device for timing a first predetermined interval to avoid valve response to a fluid-flow transient condition, first controller means responsive to completion of a timed delay by said first delay-timing means and establishing a valve-opening motor-drive connection to the motor-operated control valve of the high-demand line, and second controller means concurrently responsive to completion of said first interval and establishing a valve-closing motor-drive connection to the motor-operated control valve of the low-demand line, second resetting delay-timing means connected for operation by said second flow-measuring means for timing a second predetermined interval to avoid valve response to a fluid-flow transient condition, said first controller means being responsive to completion of a second interval by said second delay-timing means and establishing a valve-closing motor-drive connection to the motor-operated control valve of the high-demand line, and said second controller means being responsive to completion of said second interval and establishing a valve-opening motor-drive connection to the motor-operated control valve of the low-demand line.