The directive covers the following pressure equipment and accessories:

• Vessel: An enclosure for containing pressurized fluids. The vessel includes all direct attachments to other equipment until the coupling. There may be multiple chambers in a vessel.
• Steam generator: Steam generators are heated pressure equipment designed to produce steam or superheated water at temperatures higher than 110C.
• Piping: Component used to transport liquids. Piping includes a pipe or a system of pipes, tubing, expansion joints, fittings, hosing, or other pressure-bearing components. The term includes heat exchangers containing pipes for the cooling or heating of air.
• Safety accessories: Safety accessories protect pressure equipment from exceeding its allowable limits; safety valves, bursting discs, pressure switches, and temperature switches are all included.
• Pressure accessories: Devices with a pressure-bearing housing and an operational function, such as valves, pressure regulators, pressure gauges, and filters, are considered pressure accessories.
• Assemblies: Assemblies are defined as pressure equipment produced by one manufacturer to form a functional and integrated unit, such as distillation units, evaporation units, and filtration units.

A few instances where PED does not cover pressure equipment even though they are designed within the limits include:

• Equipment already regulated by the EU.
• Equipment with minor pressure hazards: low voltage machinery and devices.
• Equipment that does not exhibit any pressure hazard: water distribution system, radiators, pipe networks for hot water heating system.
• Equipment with considerable pressure hazard, but does not require inclusion in the directive: high voltage devices such as switchgear.

The key requirements of PED include:

• PED is required for pressure equipment rated for more than 0.5 bar (7.25 psi).
• For pressure equipment that do not fall under the CE categories 1-4, Sound Engineering Practice (SEP) must be used during design and production. The SEP refers to the general engineering practices followed by the member states that apply to the pressure equipment that ensures sound use and conformity to the design and manufacturing standards.
• For pressure equipment that does reach the criteria for CE categories, the basic safety requirement of the PED should be met. This may require a pressure test as proof of pressure strength. An EU/EC declaration of conformity must be prepared once the pressure test is performed and the instrument will be marked CE once all the requirements are met.
• It is not allowed to mark-up equipment. A category 2 product may not be assigned a category 3 or 4. The intention of the directive is to show the true pressure category.