Section 18(3) in The Static And Mobile Pressure Vessels (Unfired) Rules, 1981
(3)Shut-off and emergency shut-off valves .-(i) all liquid and vapour connections on vessels, except those for relief valves, plugged openings, and those where the connection is not greater than 1.4 mm diameter opening shall have shut-off valves located as close to the vessel as practicable;(ii)all liquid and vapour connections on vessels, except those for relief valves, and drainage connections of small diameter, shall have an emergency shut-off valve, such as, an excess flow valve, an automatically operated valve or a remotely controlled valve. The emergency shut-off valve shall be in addition to the shut-off valve referred to in clause (i), unless the emergency shut-off valve is a remotely controlled valve which can be operated from a safe area and shall be of a type which shall not fail:[Provided that the emergency shut-off valve is not required in cases where the connection to a vessel is not greater than three millimetre in diameter for liquid and eight millimetre in diameter for vapour, or for vessels meant for storage of non-corrosive, non-flammable or non-toxic gas;] [ Substituted by G.S.R. 141(E), dated 14.2.2000 (w.e.f. 18.2.2000).](iii)where the emergency shut-off valve is of the excess flow type, its closing rate of flow shall be below the rate which is likely to result from a fracture of the line it is protecting, calculated under the most adverse weather conditions likely to be experienced. Excess-flow valves shall have a rated flow capacity sufficiently above normal flow requirements to prevent valve chatter.
