Hydraulic turbines driven by flowing or falling water, including run-of-river installations, are covered by this heading. Tidal turbines that operate on the same hydraulic-energy principle may also fall here, but turbines driven primarily by wind or other non-hydraulic forces are classified elsewhere. The operating medium and energy-conversion principle are the key classification factors.

Regulators specifically designed to govern the speed or output of hydraulic turbines — such as governor mechanisms and wicket-gate actuators — are classified under 841090 as parts of this heading. General-purpose industrial valves or flow-control devices not dedicated to hydraulic turbine service are typically classified under their own headings in the pumps and valves section of the tariff schedule.