The excess-flow shutdown valve is used for pipeline safety isolation, when excess flow occurs.
PRINCIPLE OF OPERATION
The excess-flow shutdown valve closes when a preset differential pressure ‘dP=Pu-Pd’ exists across the valve.
The valve is powered by the line-fluid pressure with no need for external actuators, pilots, instruments or an external power source.
SHUTDOWN SETTING ADJUSTMENT
The flow-rate at which the excess-flow shutdown valvecloses, can be adjusted by varying the control orifice size ‘Do’, thus changing the valve’s differential pressure
dP = Pu – Pd
The excess-flow shutdown valve closes at a controlled speed, which is adjustable by a measuring orifice, while the valve’s flow rate reduces gradually as the valve closes by the control orifice contour.
RESETTING – EXCESSIVE DEMAND
- The excess-flow shutdown valve closes when the flowthrough the valve reaches a preset flow rate. The valve will reopen when the: –
- Over demand conditions are over.Column’s downstream is charged through the valve’s bypass
- The valve opens automatically when the downstream pressure is restored
RESETTING – PIPE BURST
The excess-flow shutdown valve closes when the flow through the valve reaches a preset flow rate. The valve will reopen when the following procedure takes place: –
- Pipe burst, causing the excess-flow conditions is rectified
- Column’s downstream is charged by the valve’s bypass
- The valve opens automatically when the downstream pressure is restored.
The excess-flow shutdown valve can be manually isolated by a removable handwheel in order to prevent unauthorised isolation.