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； Self − induced vibration is possibly caused by the semi − closed pipeline combining the automatic pressure regulator with the automatic constan 田 ow valve ， Thus ， a test was conducted on the site to analyze the generation of the coupled osciUation between the automatic pressure regulator and the direct − acting constant fiow valve ． Fumher ， the investigatiou was conducted j 皿 order to show the function of the constant flow valve ， obtain self −excited oscillation ， and to study the control measure ． Consequenlly ， when the direct − acting constant fl ow yalve is used near the setting flow ， the working mechanism activates血 e valve using the pipe pressure and the large selfLexcited oscillation can be induced． On the other hand， when the flow is smaller than that of the setting fiow of the d廿ect − acting constant flow valve ， the self − excited oscillation is not generated ． Further ， with regard to the measures to control self − excited oscillation ， it is known that self − excited oscillation is net completely restrained by merely blunting the response sensitiVity of the automatic pressure regulator ． κ eywords ； 5 θ履 一 d ・ sed pip ・line ； Aut・ matic ・ pre∬ ure ・eg ・ lat ・ r； Aut・鰄 た ・ … tantfl ・W ・ va ' レe ； Self − induced・め ・α 一 t' on ； Direct − acting constantflo 脚 alve

A field test was conducted on the stability of a pressure-reducing system combining a new type of automatic control valve in parallel with a conventional automatic control valve in a test pipeline in Ohno Mountain of Kagoshima Prefecture. The pressure control functions which include initiation of water flow and closing during transient conditions of increases and decreases in flow were investigated in a field experiment. The results were as follows: 1 When the conventional and new type automatic control valves are employed in parallel, and a safety valve is not used, the characteristics of the conventional valve take precedence. So when the flow is stopped, pressure builds up in the up-and downstream sides of the valves. 2 It is possible to combine the conventional and new type automatic control valves in a series installation. But when they are installed in parallel as a main valve and a bypass valve, respectively, countermeasure comprising concurrent installation of a safety valve to control the secondary side pressure of the control valves is needed. 3 The pressure control functions of conventional control valves are not as effective as the new type of control valve during stopped flow and very low-volume flows, so it is difficult to deal with changes in flow volume with an end valve. Furthermore, conventional control valves are slower in operation than the new type of control valve. Thus, if the conventional model is installed as the main valve in combination with the new model installed as the bypass valve, the system will no longer be dependent on the safety valve for control of secondary side pressure of the control valve. And with this, it will be possible to control the pressure in response to changes in flow rate.

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In the downstream part of the water supply system using a long open channel, a supply-demand gap occurs in which the water supply amount is smaller than the demand amount. In the agricultural water section of Aichi Canal Project, the supply-demand gap is adjusted by the upstream and downstream water level control gates that control both the upstream water level and the downstream water level of the gate. The setup method of downstream control water level of the gate enables switching between demand-oriented operation using level-reactive gate and supply-oriented operation using flow rate-reactive gate. As a result of simulation of water supply management using the upstream and downstream water level control gates, it became clear that the difference in the setting method of the gate downstream control water level affects the allocation function of the channel storage amount and the replenishment for supply-demand gap. When combining two types of downstream controlled water level setting methods, it is possible to switch to supply-oriented operation, based on demand-oriented operation, and the flow condition improvement effect is obtained.