The Tubular type turbines are usually the best choices for exploitation of tidal power and hydraulic power with extremely low heads and extremely large flow rates. They have the advantages such as large discharge, high flow speed, high efficiency and less excavation, etc. Their variations have Bulb, Pit, Siphon and S types according to their structural types.

The water diversion parts, runner and water drainage parts of Tubular turbine are on one axial line. The water flow directly and straightly through the runner without spiral casing. The water flow is axial from the pipe inlet to the draft tube outlet. 
Tubular turbine generally has two categories: fully tubular and half tubular. The half Tubular turbine is divided into bulb, pit and shaft extension types, etc.

The generator's rotor of the full tubular type unit is on the outer circle of turbine's runner, whose application is less because of its difficult sealing.

For half Tubular turbine, the generator is separate from the hydro turbine:
Tubular type: Generator set is installed inside the airtight bulb body, which has a compact structure, straight passage shape, high hydraulic efficiency and so it is widely used.
Shaft extension type tubular unit: The generator is installed outside, the main shaft of turbine extends to the outside of the draft tube.
Pit type tubular unit: The generator is installed inside a pit.

Application scope
Application scope of heads: 2m~25m
Runner diameters: 1.0m ~ 7.2m
Installable capacity: 200KW ~ 200000KW


More information
Tubular type turbine is actually horizontal installed axial flow turbine. The water from the reservoir flow through bulb head and then enter into the turbine along the passage between the outer wall of bulb body and the powerhouse concrete. The structures of tubular turbine and horizontal type axial flow turbine are basically similar. The differences between Bulb Tubular Turbine and axial flow turbine are the water diversion chamber, water distributor and draft tube.

Tubular turbine adopts conical water distributor that mainly includes the inner and outer chambers of the guide vane, guide vane, guide vane arm, connecting rod and control ring, etc. The guide blade axis of conical water distributor is layout into 60 ~ 70 degree angle with the unit axis. The bearings supporting the guide vane are seated on the guide vane inner and outer chamber. The guide vane composes a conical surface for adjusting the water flow or stooping the unit. In order to reduce the water leakage losses on the guide vane end surface, the surface of the guide vane inner and outer chamber are spherical surface.

Bulb or tubular turbines are designed into the water delivery tube. A large bulb is centered in the water pipe which holds the generator, wicket gate and runner. Tubular turbines are a fully axial design, whereas Kaplan turbines have a radial wicket gate.

Pit turbines are bulb turbines with a gear box. This allows for a smaller generator and bulb.

S- turbines eliminate the need for a bulb housing by placing the generator outside of the water channel. This is accomplished with a jog in the water channel and a shaft connecting the runner and generator.