Comparison between Impulse Turbine and Reaction Turbine

Impulse and reaction turbine are compared below presented in picture and tabular form.

Schematic diagram summarising the differences between impulse turbine and reaction turbine, where the rotor is the rotating part and the stator is the stationary part of the machine. Image source: Emoscopes (Wikimedia Commons)

Differences between Impulse and Reaction Turbines:

 

S.No	Impulse Turbine	Reaction Turbine
1	In impulse turbine all hydraulic energy is converted into kinetic energy by a nozzle and it is is the jet so produced which strikes the runner blades.	In reaction turbine only some amount of the available energy is converted into kinetic energy before the fluid enters the runner.
2	The velocity of jet which changes, the pressure throughout remaining atmosphere.	Both pressure and velocity changes as fluid passes through a runner. Pressure at inlet is much higher than at outlet.
3	Water-tight casing is not necessary. Casing has no hydraulic function to perform. It only serves to prevent splashing and guide water to the tail race.	The runner must be enclosed within a watertight casing.
4	Water is admitted only in the form of jets. There may be one or more jets striking equal number of buckets simultaneously.	Water is admitted over the entire circumference of the runner.
5	The turbine doesn’t run full and air has a free access to the bucket.	Water completely fills at the passages between the blades and while flowing between inlet and outlet sections does work on the blades.
6	The turbine is always installed above the tail race and there is no draft tube used.	Reaction turbine are generally connected to the tail race through a draft tube which is a gradually expanding passage. It may be installed below or above the tail race.
7	Flow regulation is done by means of a needle valve fitted into the nozzle.	The flow regulation in reaction turbine is carried out by means of a guide-vane assembly. Other component parts are scroll casing, stay ring runner and the draft tub.
8	Example of impulse turbine is Pelton wheel.	Examples of reaction turbine are Francis turbine, Kaplan and Propeller Turbine, Deriaz Turbine, Tubuler Turbine, etc.
9	Impulse turbine have more hydraulic efficiency.	Reaction turbine have relatively less efficiency.
10	Impulse turbine operates at high water heads.	Reaction turbine operate at low and medium heads.
11	Water flow is tangential direction to the turbine wheel.	Water flows in radial and axial direction to turbine wheel.
12	Needs low discharge of water.	Needs medium and high discharge of water.
13	Degree of reaction is zero.	Degree of reaction is more than zero and less than or equal to one.
14	Impulse turbine involves less maintenance work.	Reaction turbine involves more maintenance work.