An appliance designed with a provision for a vent permanently open to the atmosphere. These types of systems are often marketed as "low" or "medium" pressure units and their installation is characterised by "risers" or vent pipes in place of a PTR Valve. These vents ensure that the units supply hot water at satisfactory pressure without excessive pressurisation of the water heater vessel. Water heaters of this type may be connected to mains pressure cold water but this installation involves special valves to ensure that the vessel is not subject to full mains pressure. This reduced pressure of operation may not be sufficient to supply more than one outlet at a time and may not provide sufficient flow to shower roses etc.
supplied with a vent or vents for intake of air or discharge of gases
Describes the fact that the brake disc was designed in such a way that heat and gases produced when applying the brake are more easily dissipated. This helps to obtain a steady and predictable braking performance.