| 摘要 |
PURPOSE:To reduce both switching frequencies and the wear of a valve and then to shorten the switching time, by having the hysteresis with different loss coefficients with which a primary valve action is switched to a secondary valve action and vice versa. CONSTITUTION:A primary valve 2 and a secondary valve 3 are provided to a water pipe 1 and a by-pass pipe 4 respectively. The valve 3 is fully opened with a small loss coefficient, and the control is performed with the valve 2. While the valve 2 is fully opened with a control of the valve 3 for a large loss coefficient. The control is possible with either the valve 2 or 3 in a section during which the equivalent synthetic loss is set at an intermediate value. The loss coefficient etac is calculated 8 with comparison 9 and discrimination 10 through a flowmeter 5 and a pressure transmitter 6. Then the openings are calculated 13 and 11 for the valves 2 and 3 to be set 14 and 12, and these openings are compared 15 with each other. A motor 16 is driven via a driving circuit 17. As a result, the open/close of the valves 2 and 3 due to the increase/decrease of the loss coefficient draws a hysteresis. This reduces both switching frequencies and the wear of the valves, and the switching time is shortened. |
