Many of the water and liquid fuel tankers have the container in an elliptical cross section. But for the same surface area a perfect cylindrical cross section container would have more volume. Then why is the elliptical cross section preferred?

V.K. PRAHLADA RAO

Bangalore

There are a number of factors which affect the shape of a liquid carrying tank. Most important one is the stability of the vehicle on the move while taking a turn on the road. To have maximum safety factor, the centre of gravity of the loaded vehicle has to be as close as possible to the ground.

This is achieved by adopting an elliptical shape of cross section of the tank. In fact the height of the centre of gravity will be least for a rectangular cross section.

But then there are other problems with a rectangular section like presence of corners (leading to cleaning problems), large number of joints and larger area of metal sheet for the same volume of the tank.

An elliptical section also provides maximum stability against liquid movement inside the tank on account of lateral acceleration.

Then the question is why there are some tanks which have circular section. In fact for vessels which contain pressurized liquids or gases like LPG or PNG, the circular section is the most efficient section which gives maximum strength against internal pressure.

In such cases the strength of the tank may be the governing factor to decide the shape of the tank. That is why we find circular section tanks for carrying LPG or similar contents.

S.P.S. JAIN

Former Member, Engineering, Indian Railways

Greater Noida, Uttar Pradesh

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