| 摘要 |
PURPOSE:To reduce the switching frequency of electromagnetic valves and to increase the durability of a device, by giving the switching control to only one of plural electromagnetic valves with the necessary duty with other electromagnetic valves opened fully and thus improving both the flow rate and control properties. CONSTITUTION:Electromagnetic valves 13a-13c are connected in parallel; a differential pressure control valve 16 holds the differential pressure between the upper and lower flows of the electromagnetic valves at a prescribed level; and a controller 20 controls the switching of the valves 13a-13c. Then a switching signal of 100 duty is delivered to N-1 units of electromagnetic valves that satisfy an equation (N-1)QO<=Q<N.QO, where Q is the required flow rate, QO is the flow rate per electromagnetic valve in the case of the duty 100 and N is a positive integer respectively. At the same time, the switching signal having the duty which is set to obtain the flow rate of Q-(N-1)QO is delivered to an electromagnetic valve excepting the above-mentioned N-1 units of the electromagnetic valve. |
