Studies on self-induced vibration of automatic pressure regulator and constant flow valve in the semi closed pipeline

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Semi-closed pipeline that combines an automatic pressure regulator with an automatic constant flow valve is introduced with the aim of achieving an optimum solution between the scale of the agricultural pipeline system and water control. This pipe line attempts to reduce excess pressure by the use of the automatic pressure regulator ; it also uses the chloroethene tube.Further, the use of the automatic constant flow valve that is arranged in the downstream can exclude the effect of the extra watershed management located at the end. However, there exists a possibility that the system combining the automatic pressure regulator with the automatic constant flow valve can generate self-induced vibration.When the demonstration was conducted at the site and the condition of self-induced vibration was verified, it was observed that a large self-induced vibration is not generated when the flow is smaller than the setting flow of the direct-acting constant flow valve. On the other hand, when the direct-acting constant flow valve is used near the setting flow, the working mechanism is used to activate the valve using the pipe pressure and the large self-induced vibration can be generated.Further, with regard to the measures to control self-excited oscillation, it is known that self-excited oscillation is not completely restrained by merely blunting the response sensitivity of the automatic pressure regulator.It is also known that when the safety valve installed in the upstream and downstream is of a small scale, the pressure vibration does not damp even if the safety valve is activated.