Red Seal Gasfitter Class B key terms

Pressure expressed relative to the chosen local atmospheric reference, rather than relative to a complete vacuum as with absolute pressure.

The difference between pressures at two specified points, whose sign depends on the reference and the instrument port connections.

A defined comparison or adjustment process used to establish an instrument’s measurement performance against the applicable reference and specification.

The controlled separation and verification of relevant energy sources before work, including consideration of stored pressure or electrical energy.

Documentation of the installation’s measured conditions, test methods, operating checks and restrictions needed to establish and communicate its verified status.

The combined demand of equipment served by a piping section under the assumptions and allowances of the applicable sizing method.

The reduction in pressure associated with flow through a system section, influenced by flow rate, dimensions, length, fittings and operating conditions.

A standardized size designation that must not be assumed to equal the exact inside diameter for every material and wall specification.

A change, commonly a decrease, in controlled outlet pressure as flow demand increases under the regulator’s stated inlet and operating conditions.

The regulator’s stabilized downstream pressure at no flow under its specified test conditions, distinct from the outlet pressure measured during demand.

Air mixed with fuel upstream of the burner flame ports in the particular burner design, before the initial mixture burns.

Additional air reaching the flame after the initial fuel-primary-air mixture leaves the burner ports, supporting the designed combustion process.

Combustion air beyond the theoretical chemical requirement, used to support actual mixing but capable of increasing heat loss when excessive.

Combustion-product flow driven by buoyancy pressure from density differences between the vent gases and the surrounding air, against system resistance.

The portion of an opening actually available for airflow after accounting for the obstruction of a grille, screen or similar component.

A contact shown open in its defined unactuated reference state, which can change when the associated relay or mechanism operates.

A flame-proving method that detects the small asymmetric electrical current through a suitable flame and the designed sensing and return path.

A device or circuit condition that permits or prevents a stage of operation according to the system’s intended sequence and requirements.

The defined control-sequence interval for attempting to establish and prove ignition, followed by the specified response if proof is absent.

A protective control intended to respond to a specified abnormal condition, rather than provide only the system’s ordinary demand regulation.

The energy rate supplied by fuel under the stated measurement basis, distinct from the useful heat rate delivered to the intended load.

The portion of input energy delivered as the intended useful effect under the stated conditions, used when calculating the corresponding efficiency.

The outlet temperature minus the inlet temperature for the stated flow path, related to heat transfer and mass flow under defined conditions.

The approved process for taking equipment or a system branch out of service and leaving it safely isolated, closed and identified as required.

The designed propagation of ignition between burner sections through the intended passages or arrangement, affected by cleanliness and correct assembly.