| 摘要 |
PURPOSE: To return a control valve to a control range again at the development of a pressure peak after the control valve runs away from the control range by setting the cross section of a safety hole always small compared with the return strength of a spring in the full opening. CONSTITUTION: A valve casing is provided with two connected conductors at an entrance side, and those connected conductors are opened in the valve casing 1 by a control opening 8 or a safety hole 16. An oil conductor at the entrance side is connected through the control opening and the variable open cross section of the safety hole with the oil conductor at an exist side independently of the position of the axial direction of a control piston. That is, a control piston 9 is provided with two control edges 10 and 17, and one control edge 10 cooperates with the control opening 8 and the other control edge 17 cooperates with the safety hole 16. The cross section of the safety hole is made always small compared with the return strength of a spring so that a pressure difference acting on the control piston can exist. Thus, the control piston can be returned to the control range again by the spring strength.
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