1. In this Act, unless otherwise required by the context, the expression “pressure vessel” designates any of the following apparatus, including the plumbing and accessories used for its operation:(1) a boiler or furnace, operated by steam or hot water or by another liquid or gas;
(2) an automatic apparatus for heating a boiler or furnace;
(3) a refrigerating plant; and
(4) a tank or a vessel containing a gas or a liquid under pressure.