What is a Draft Tube?

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  • Written By: Alexis W.
  • Edited By: Heather Bailey
  • Last Modified Date: 18 September 2016
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A draft tube is one important part of a turbine, which is used to transform water into energy. It's found within the piping system in jets, dams, or anywhere else where turbines help do difficult mechanical work. Turbines need to have a minimum amount of water to propel them in order to produce enough energy. Without these tubes, the pressure could drop because of lack of water, and in turn, the entire turbine could fail to work and power could be lost.

The primary purpose of the draft tube is to monitor the influx of water. The turbine has something called a "tail race," which is the lowest portion of a dam or construction project where water pools. The tube connects the turbine to this tail race, permitting the turbine to be outside of the water but still have access to the water.

A draft tube can be relatively simple to construct, but it must be strong and tough enough to withstand the elements and the work of the turbines. One can also be either straight or curved, depending on the general construction of the turbine.


With this part, it is possible to maintain the important column of water that keeps the turbine running. The right water level can be maintained despite any potential lack within the amount of material that flows into the machine. In this matter, the tube can help keep the inflow of water into the turbine regular, even if water levels drop, so that the turbine can run properly with the correct amount of pressure maintained.

Often, draft tubes have to be installed underneath a dam, plane, or other machinery that is controlled by the work of the turbine. They must be strong enough to withstand the pressure placed on them. If they are installed or repaired after the turbine is already functioning, sometimes they must be placed while other parts are working as well — sometimes even while air, gas or water is already flowing through the turbine. They have to be put into place in the turbine through careful movement along the edge of the equipment as a result.


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Post 5

Is this like, by decreasing pressure at the outlet, draft tubes increase the pressure at the inlet which was earlier at atmospheric pressure. So now, water enters at a pressure higher than atmospheric pressure, which is called increased pressure head. So K.E., which is being wasted at the outlet is utilized to convert into the pressure head, thereby increasing efficiency.

Post 4

As the area increases, it creates a pressure difference from the inlet to the outlet of the draft tube as a result of which the inlet is at higher pressure than the outlet of the draft tube. As per the continuity equation, liquid flows due to the pressure difference.

Post 2

It is really helpful, but I need to know why draft tubes have increasing cross sections and why they prefer elbow type shapes?

Post 1

it is really impressive and i need more about the control portion of the draft tube means, how it regulates the inflow water and what is the velocity maintained at that particular level.

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