In recent years the pump-turbine hydraulic machine has been developed.
It is very similar in design and comstruction to the Francis turbine.
When water enters the rotor at the periphery and flows inward the machine acts as a turbine.
With water entering at the center (or eye) and flowing outward, the machine acts as a pump.
The direction of rotation is, of course, opposite in the two cases.
The pump turbine is connected to a motor generator which acts as either a motor or generator depending on the direction of rotation.
The pump turbine is used at pumped-storage hydroelectric plants which pump water from a lower reservoir to an upper reservoir during off-peak load periods so that water is available to drive the machine as a turbine during the time that peak power generation is needed.
An example of a pump turbine is that at the Kisenyama Pumped Storage
Project of the Kansai Electric Company in Japan.
There are two identical pump turbines at that installation.
Under the normal range of operating conditions each machine has the following characteristics,
As a turbine (n = 225 rpm):
Develops 241,000 kW at maximum net head of 220 m
Develops 178,000 kW at minimum net head of 185m
As a pump (n = 225 rpm)
Delivers 110 m^3/s at minimum net head of 197 m.
Delivers 86 m^3/s at maximum net head of 230 m.
When operating as a turbine these machines have a specific speed n_s = 133.
As a pump, these machines have n_s = 40 (Sec. 17.5).