Valve with heat-responsive bearing assembly providing back seat arrangement

For a normally non-rising stem valve having a valve stem which passes out of a chamber in a valve housing through a bonnet having a passageway in which a packing assembly normally seals between the valve stem and the bonnet and in which a bearing assembly journals the valve stem for rotation relative to the bonnet and a retainer means secures the bearing assembly relative to the bonnet against substantial axial movement of said valve stem and of said bearing assembly,

• the improvement wherein:
• the retaining means includes a bonnet gland secured to said bonnet and surrounding the bearing assembly;
• the retaining means further includes a retainer secured to the bonnet gland relatively exteriorly of the bearing assembly;
• and
• the retaining means further includes a body of relatively low temperature fusible material physically axially interposed between said retainer and the bearing assembly, said body being in the form of a washer-like annulus;
• said improvement further comprising channel means out through which said fusible material may run when subjected to a predetermined amount of relatively low temperature heat, so that when the fusible material has run out, the valve stem is free to rise to a limited extent;
• and
• said improvement further comprises an annular first metal sealing surface circumferentially provided on said valve stem and a second metal sealing surface provided on said bonnet within said chamber, which two sealing surfaces normally remain spaced axially apart but which become annularly engaged in a sealed condition upon rising of said valve stem by said limited extent;
• the bonnet gland comprising a tubular member having an internally threaded outer end portion and said retainer comprising an externally threaded tubular retaining gland threaded into the outer end portion of the bonnet gland;
• said valve stem including a radially outwardly projecting flange and said bearing assembly including a first bearing ring below and in contact with that flange and a second bearing ring above and in contact with that flange;
• and
• a tubular spacer means interposed between the second bearing ring and the annulus of fusible material.