What is an Excess Flow Valve, and why it is required in Flammable & Toxic Gas Systems?

What is an Excess Flow Valve, and why it is required in Flammable & Toxic Gas Systems?

02 January, 2022


An excess flow valve is a self-regulating safety device installed in a gas service line to automatically latch off the flow of gas / liquid in the event of a significant break, puncture, or severance in the line. Their primary function is to automatically stop the excessive flow of the tank’s liquid or gas contents in the event of a flow line rupture or system failure. Whenever there is a fault in a line like leakage or failure, EFCV designed to shut off the supply of the gas. When the liquid or vapor passing through it exceeds a prescribed flow rate, EFCV shuts down the gas supply. EFCV are also known as velocity check Valve, emergency shutdown device, seismic valve, surge preventer, and line rupture valve.


These valves are used to prevent disasters which can occure in case of rupture of pipeline/ Flexible hoses in working conditions. Excess Flow Check Valve isused to secure damage which can be caused due to large leaks and breaks in a pipeline.


These valves are recommended by several authorities/ standards like OISD, IS-6044 Part 1 & 2, NFPA58, PNGRB, & PESO etc.


How does an excess flow valve function?

Excess flow valves function similarly to electrical circuit breakers, which trip when the current exceeds a preset limit. An excess gas flow trips the excess flow valve, causing a spring-loaded device inside the valve to automatically restrict gas flow. When the reason of excess flowing is repaired, or the service line pressure is similar in both side of valve is equal, the valve automatically resets or reopens.


Where to be install an EFCV ? 

The EFCV is installed in the service line that connects the gas/liquid main. The EFCV is installed as close to the gas/ liquid main as possible in most cases. To accommodate interference from other buried structures, the location may need to be installed further away from the gas /liquid main in some cases. These valves also recommended in some cases in line before Pressure gauge, drainage valve etc.


How to select the size of an EFCV?

It is critical to select the proper closing flow rating for the excess flow check valve to function correctly. If a line or fitting ruptures downstream of the valve, if the rating is too high, the valve may fail to close. If the rating is low, the valve will shut prematurely during pump start-up or when there is a surge of fluid. We recommend contacting SEPL to determine the appropriate flow rating for your specific application. As a general rule, a spring with a closing flow rate that is roughly 50% higher than the average expected flow will provide enough margin to let the valve to close in the occurrence of a catastrophic event while eliminating nuisance closings.


Because excess flow check valves rely on flow to close, the line downstream of the valve should be as concise and free of bends and other flow restrictions as possible. Lines and fittings should not be receded to smaller than the valve’s intended line size. As a general rule, 10 diameters of straight piping should be installed downstream of the valve.


Why choose SEPL?

At SEPL, we are constantly evolving our products to meet the ever-changing demands of our customers, and our team is always conducting new research and development to bring revolutionary products that will change the consumer’s perception.
We believe that our customer is our top priority, and we have pledged to raise the consumer experience to new heights to set a market standard.

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What is an Excess Flow Valve, and why it is required in Flammable & Toxic Gas Systems?


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