A single-stage impulse turbine is known as a de Laval turbine.

• It is the first working impulse turbine.
• These turbines are mostly used for small power and high-speed purposes.
• It consists of a single rotor to which the impulse blades are attached.
• The high-pressure steam will be fed through one or several convergent-divergent nozzles.
• At any given instant of time, only a few blades receive steam from the nozzles.
• The rotor speed can be controlled by closing one or more nozzles which are known as governing of the turbine.
• The entire steam pressure drops in the nozzle increasing the velocity of the steam to the maximum possible extent.
• The velocity decreases when the steam moves over the blades to produce rotary mechanical power.
• It consists of a single set of nozzle and moving blades.
• Therefore, total pressure drop from boiler pressure to condenser pressure takes place in a single nozzle which gives high rotational speed exceeding the pressure limit of 3000 rpm.