Excess flow valves are valves that automatically close due to a high fluid flow condition. They are sometimes refered to or branded as a flow fuse, due the analogy with an electrical fuse stopping the flow of elctricity due to a high current condition. Once the valve is "tripped" the flow is blocked completely and the valve is held in the closed position by the upstream pressure until it is equalised or nearly equalised with the downstream pressure. Some of our larger excess flow valves are equipped with manual bypass valves which allow pressure equalisation without depressurising the upstream system. Call us today if you require a quotation or technical assistance regarding excess flow valves.