EXCESS FLOW SHUT-OFF VALVES


EXCESS FLOW SHUT-OFF VALVES

Excess Flow Shut-Off Valves are designed to automatically shut-off the delivery of gas in a line if the flow exceeds a preset limit. They are commonly used as a safety device to protect a system from excess flow in the event of equipment failure or to protect personnel and property in the event of a line rupture. The capability of operating from 10 to 3500 psi allows them to be used either in high or low pressure applications. An excess flow shut-off valve is an isolating valve which is flow sensitive. Under normal operating conditions the valve is open and fluid flows with a slight pressure drop. In the event of process control failure or pipe/vessel fracture the normal fluid flow rate can increase dramatically and very serious consequential damage can ensue. Incorrect proportions of chemicals being mixed can lead to devastating results. Fluids flowing from open pipes and vessels can create dire personnel hazards or permanent environmental damage. Costly products can be lost for ever. The excess flow shut- off valve senses fluid velocity higher than required and isolates the system. The higher fluid velocities create increased fluid drag within the valve and produce sufficient force to close the valve. Figure 5.8 shows a typical liquid excess flow design. Valves up to DN600 have been produced. Pressure ratings are not a problem as the valve body has no openings around the periphery. Valves can be manufactured in most materials to suit the process. Once closed, the excess flow shut-off valve must be reset before it will open. To reset the valve, the pressure on both sides must be equalized: this can easily be achieved by a small by- pass.

SAFETY / PRESSURE RELIEF VALVES  THERMAL RELIEF VALVE    ATMOSPHERIC RELIEF VALVE   PRESSURE REDUCING VALVES / STATION   PRESSURE CUM VACUUM RELIEF VALVES  BREATHER VALVES   EXCESS FLOW CHECK VALVES    UNDERGROUND SAFETY VALVES FOR WATER TANK /  WATER FLOW CANAL AS PER BS – 4558 : 1983 NON – RETURN VALVES  BALL VALVES DIAPHRAGM VALVES  NEEDLE  VALVES / MANIFOLDS/ THROTTLING VALVES   FLUSH BOTTOM VALVES