Valve with heat seal - has fusible metal gasket to release valve stem for metal to metal seal at high temperatures

摘要

The bearing of a normally non-rising stem gate valve has an annulus of fusible material. Upon subjection to a preselected temperature level, the fusible body melts out of the way, permitting the stem to raise slightly, making up a metal-to-metal seal between the valve stem and bonnet. This prevents loss of sealing normally provided by the valve stem packing. It has a channel through which the fusible material may run when subjected to a predetermined amount of relatively low temperature heat.