A Globe Valves, particularly for high pressure, high temperature steam, is equipped with an exterior bypass line for hydraulic balancing. The GLOBE VALVE has a pneumatic operator and biases a valve plug closed by a spring. A guide for the valve plug is fitted at its lower end with a ring so that only a small amount of steam flows between the ring and the plug when the valve is closed or nearly closed; but, when the valve is open, steam flows between the plug and the ring faster than it can be evacuated by the bypass line. The steam flowing past the ring pressurizes a chamber at the top of the plug. The bypass line includes a pneumatically operated valve. When the main valve is to be opened, the bypass valve is opened, and remains open, to evacuate the chamber and begin balancing the hydraulic forces on the valve plug. The lower end of the plug is undercut, so that after partial opening of the valve, enough steam flows into the chamber to pressurize it again for assisting the next reclosing. During closing, the bypass valve remains open until the closing cycle is completed. Thus, when the plug approaches closed position, the supply of steam to the chambeis reduced and the pressure therein drops to cause hydraulic balancing again and thereby prevent the plug from slamming closed. Thereafter, the bypass valve closes and the chamber pressure increases to hold the plug tightly closed.

MORE NEWS