Every boiler shall be provided at least with the following:-

Two safety valves, one of which may be a high steam and low water type safety valve. In no case should the bore of the seat of the valve be less than 19 mm (¾");

Two means of indicating water level;
A steam pressure gauge;
A steam stop valve;
A feed check valve;
One feed apparatus. When the heating surface exceeds 200 square feet-two independent feed apparatus, each such apparatus shall have a capacity of not less than the maximum continuous rating of the boiler. (For boilers in battery see regulation 336A), and
A blow –down cock or valve;
Fusible plugs as provided under Regulation 331;
An attachment for Inspector’s test gauge;
A manhole, where size and construction permit, and such mudholes or sightholes as are necessary for effectively cleaning the boiler.

In the case of boilers fitted with integral superheaters, an additional safety valve shall be fitted at the end of the superheater outlet header.

In the case of boilers with no fixed steam and waterline, the fitting of such accessories that are manifestly not needed or used, such as water gauges, water columns and gauge cocks, may not be insisted upon.

Two independent feed apparatus mean  feed apparatus to which power is supplied from two independent sources or from a main or mains to which two sources of generation are connected or from a common steam main fed by two or more active boilers or, a combination of any of the above.

*NOTE.-It is recommended that in Lancashire and Cormish Boilers one of the safety valves should be of high steam and low water type. In Water Tube and Horizontal Multi-tubular Boilers, a low water alarm directly operated by steam should be fitted. Rams-bottom type safety valves consisting of two valves and with spring and lever in common may be considered as two safety valves for the purpose of this Regulation.

In the case of Marine Type boilers low water alarm may be fitted in place of a fusible plug.

In the case of automatic or semi-automatic oil-fired or gas fired boilers, low water alarms may be fitted in preference to fusible plugs provided such boilers are equipped with automatic tripping device to disconnect fuel supply and to start the feed pump simultaneously in the event of low water in the boilers.

In the case of a single boiler of the shell Type and not connected in a battery with other boilers, the heating surface of which does not exceed 102² (1,00 sq. ft.), two independent source of power supply to the two feed apparatus will not be necessary.

In the case of miniature boilers coming under Chapter XIV the Steam pressure gauge may be connected to the steam space or to a steam connection to the water column by a syphon tube or equivalent device that will keep the gauge tube filled with water. If brass or bronze composition is used the minimum size of the syphon tube shall be 6mm.(¼ in.) standard pipe size; for other materials the minimum inside diameter of the pipe or tube shall be 13 mm ( ½ in.).

For Electrode boilers, see Regulation 437.