(a) Number and capacity.

Every boiler or steam reservoir shall be equipped with at least two safety values, the capacity of which shall be sufficient to prevent, under any condition of service, an accumulation of pressure more than five per cent above the allowed steam pressure.

(b) Setting of safety valves.

Safety valves shall be set to pop at pressures not exceeding six pounds above the working steam pressure. When setting safety valves two steam gauges shall be used, one of which must be so located that it will be in full view of the person engaged in setting such valves; and if the pressure indicated by the gauges varies more than three pounds they shall be removed from the boiler or steam reservoir, tested, and corrected before the safety valves are set. Gauges shall in all cases be tested immediately before the safety valves are set or any change made in the setting. When setting safety valves the water level in the boiler or steam reservoir shall not be above the highest gauge cock.

(c) Time of testing.

Safety valves shall be tested under steam at least once every three months and also when any irregularity is reported.