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* Hydraulic control valve system manipulating a 12" ball valve to regulate pump discharge and suction pressures on a gas pipeline.
* PLC output to the control valve system is -8 mA to +8 mA; where a negative signal closes the valve, a positive signal opens the valve, and 0 mA maintains the current position.
* Currently using Proportional only control (assuming bias is "built-in" to valve; it stays put at zero output).
* Problem 1: When opening or closing the valve and a change in valve direction is required, the mA signal must come all the way back to and cross over 0 mA to get the opposite action from the valve. Sloppy!
* Problem 2: At times, line conditions dictate that the discharge pressure cannot be maintained at setpoint. The control valve will open to 100%, but will have not have much effect on the pressure. When conditions change and the pressure rises again, not only does the mA signal have to decrease below 0 mA to begin closing the valve (see problem 1) the ball valve must travel from 100% to about 35% before any change in pressure is seen. Sloppy! Limiting the maximum open position of the valve is not an option because of the wear and tear it would cause on the ball.
Currently, intermediate setpoints are used to prevent the pressures from overshooting (discharge) or undershooting (suction) at startup.
Any suggestions would be greatly appreciated.
* PLC output to the control valve system is -8 mA to +8 mA; where a negative signal closes the valve, a positive signal opens the valve, and 0 mA maintains the current position.
* Currently using Proportional only control (assuming bias is "built-in" to valve; it stays put at zero output).
* Problem 1: When opening or closing the valve and a change in valve direction is required, the mA signal must come all the way back to and cross over 0 mA to get the opposite action from the valve. Sloppy!
* Problem 2: At times, line conditions dictate that the discharge pressure cannot be maintained at setpoint. The control valve will open to 100%, but will have not have much effect on the pressure. When conditions change and the pressure rises again, not only does the mA signal have to decrease below 0 mA to begin closing the valve (see problem 1) the ball valve must travel from 100% to about 35% before any change in pressure is seen. Sloppy! Limiting the maximum open position of the valve is not an option because of the wear and tear it would cause on the ball.
Currently, intermediate setpoints are used to prevent the pressures from overshooting (discharge) or undershooting (suction) at startup.
Any suggestions would be greatly appreciated.