(f) A space of at least three-quarters of an inch must be allowed between the sides of the tank and the bell.
(g) All water-seals must be so arranged that the water-level may be readily seen and maintained.
19. WATER-SUPPLY.--(a) The supply of water to the generator for generating purposes must not be taken from the water-seal of any gasholder constructed on the gasometer principle, unless the feed mechanism is so arranged that the water-seals provided for in Rules 18, (c), (d), and (e) may be retained under all conditions. This provides for the proper level of water in the gasholder.
(b) In cases where machines of the carbide-feed type are supplied with water from city water-mains or house-pipes, the pipe connexion must discharge into the regularly provided filling trap on the generator and not through a separate continuous connexion leading into the generating chamber.
This is to prevent the expulsion of explosive mixtures through the filling trap in refilling.
20. RELIEFS OR SAFETY BLOW-OFFS.--(a) Must in all cases be provided, and must afford free vent to the outer air for any over- production of gas, and also afford relief in case of abnormal pressure in the machine.
Both the above-mentioned vents may be connected, with the same escape- pipe.
(b) Must be of at least 3/4-inch internal diameter and be provided with suitable means for connecting to the pipe loading outside of the building.
(c) Must be constructed without valves or other mechanical working parts.
(d) Apparatus requiring pressure regulators must be provided with an additional approved safety blow-off attachment located between the pressure regulator and the service-pipes and discharging to the outer air.