| 摘要 |
<p>A fluid control valve of the pilot operated kind has a main valve comprising a valve seat and valve member. The valve member is moved by piston action in response to fluid pressure in a control chamber. The control chamber may be coupled to the upstream pressure or the downstream pressure to close or open the valve respectively. When the valve is open there is a bleed of fluid through the control chamber via inlet and outlet passages from the upstream side and to the downstream side of the valve respectively. An auxiliary valve is situated in the downstream passage and effects control of the main valve The auxiliary valve may be an on/off valve or a continuously controllable valve whereby the operating position of the main valve member may be controlled at an intermediate position automatically to limit flow rate.</p> |
