# Sonic Choking in Gas Networks

Sonic velocity CANNOT be attained by a gas as it flows through a pipe of constant cross-sectional area. Sonic choking occurs when the flowing gas experiences a local velocity equal to the sonic velocity of the gas at that temperature and pressure. Within any piping system sonic choking can only occur at locations where the gas attempts to accelerate beyond the local sonic velocity. This can only occur at locations where the flow path cross sectional area experiences a change. Examples of these types of locations are: ▪Endpoint choking occurs as flow exits a pipe into a vessel or to atmosphere. FluidFlow automatically detects this condition and limits mass flow accordingly. ▪Sonic choking can also occur through any of the Size Change components, for example a nozzle, expansion or orifice plate. FluidFlow detects this condition and again limits mass flow accordingly.