Section 18(4) in The Static and Mobile Pressure Vessels (Unfired) Rules, 2016
(4)Liquid level gauging device-(i)a vessel used for liquefiable gas or dissolved gas shall be equipped with a liquid level gauging device to afford ready determination of the amount of liquid in the vessel at any time;(ii)all liquid level indicators shall be suitable for operation at the design pressure of the vessel;(iii)every vessel shall, in addition, be equipped with a fixed maximum level indicating device depending upon the liquefiable gas or dissolved gas filled in the vessel;(iv)gauging devices that require bleeding of the contents of the vessel such as a rotary tube, fixed tube and slip tube shall be designed in such a manner that the same cannot be completely withdrawn in normal gauging operations.
