Excess flow valves

Fit an excess flow valve to the outlet of a regulator, selected to allow the maximum required gas flow. 

Freeman, R. A. and Shaw, D. A., Sizing Excess Flow Valves, Ibid., p. 176. 

Piping Rating, Codes, Cross-Connections, Purging, Excess Flow Valves... 

Can passive leak-limiting technology (e.g., blowout resistant gaskets and excess flow valves) be utilized to limit potential for loss of containment ... 

Are excess flow valves plainly and permanently marked with name of manufacturer, catalog number, and rated capacity ... 

Are loading/unloading lines fitted with backflow check or excess flow valves ... 

Are all liquid and vapor connections to containers, except safety relief valves, liquid gauging, and pressure gauge connections fitted with orifices not larger than No. 54 drill size, equipped with excess-flow valves ... 

Excess flow valves provide automatic isolation when pipe failures occur. For these valves to be effective, the downstream piping must have a flow capacity greater than the set point of the excess flow valve. The main advantage of these valves is that they operate automatically to stop leaks and do not require fire conditions to be present for them to close. For example, in FNG service, excess flow valves can limit the maximum possible leak rate to protect nearby areas. 

Isolation devices, such as manual/automatic valves, check/excess-flow valves, dry-break couplings, which shut off flow if the coupling is parted, and positive displacement pumps, which stop flow when shut down ... 

In some cases, after careful evaluation, other valves may be considered for EBVs such as spring-loaded control valves that fail closed, back flow check valves (these are not normally considered reliable enough for EBVs by many engineers), and excess flow valves. Excess flow is the loss of material from the confined environment of a vessel or pipeline. Two approaches are available for the detection and valve action of excess flow valve systems (1) External, where excess flow is detected outside the valve itself, and (2) internal, which is within the valve unit and has limited applications. Excess flow conditions are detected more readily because of loss of resistance to flow than because of loss of pressure. All excess flow detection systems are based on product physical properties as well as flow rate. A change of products or process conditions may require a change in the excess flow detection system. For example, a number of excess flow valves are rated for low pressure and are made of materials not suitable for hydrocarbons. 

If, after careful review, it is necessary to use a transparent device that could result in a hazard if broken, design safeguards should be used such as (1) shields or covers, (2) extra-strong devices (such as 300 psig equipment in 100 psig service), or (3) suitable excess-flow valves or remotely operated isolating valves. 

Remotely Operated Shutoff Valves These should be considered for supply lines and other vulnerable pipelines. Excess flow valves that close when flow exceeds a set amount are possible substitutes, but they are not acceptable to some operators. 

Excess-flow valves, to limit the dmation of a high-rate leak... 

Benz, G.R. Sinclair, T.A. Development and Use of Excess Flow Valves in LPG Industry. Petroleum Refiner, February 1945, p. 52. 

---