Excess flow limiting valve

摘要

A conduit coupling includes an improved plug assembly. The plug assembly has a valve which limits excess flow in the direction of normal flow and prevents backflow in the opposite direction. The valve includes a valve member which is operated from a first closed condition to an open condition in response to a pressure differential caused by normal flow. The valve member further moves to a second closed condition in response to a predetermined pressure differential across the valve member which would result in an excess flow in the downstream direction. The valve member operates from its open condition to the first closed condition whenever the difference between the upstream pressure and the downstream pressure is less than a predetermined amount, thus preventing backflow. A leak down passage is provided which allows fluid to flow through the valve assembly even when the valve is closed. This enables the valve member to return to its normal open position after there has been an excessive fluid flow by allowing fluid to flow from a high pressure side to a low pressure side of the valve member to reduce the pressure differential.