| 摘要 |
<p>The gate valve has a backseat which is made up only when the normally non-rising operator stem is permitted to rise a short distance. A smaller-dia. stem may be used than one which is of sufficient area where it passes through the stem packing to cause the internal pressure within the valve cavity to generate sufficient force to overcome the frictional forces resisting stem movement developed by the internal pressure between the gate plates and the seats. To make the stem rise when it is supposed to, to make the backseat, a system of clearances is provided between the stem nut and the gate plates. A different stop arrangement is shown for limiting rising of the gate, for defining the fully open position of the gate.</p> |
