Assuming you mean something like [this](https://www.geograph.org.uk/photo/1899640), that’s the frame of a gas holder or [gasometer](https://en.wikipedia.org/wiki/File:Gasometer.svg), which was a form of flexible storage container for gas. The ring and stands were guides for the upper shell of the gasometer as it rose and fell. The rise and fall were driven by the amount of gas in the “tank”: the more gas in the tank, the higher it rose.
This kind of storage solution was useful in the early days of coal gas because it kept the gas at near atmospheric pressure, so the pressure of gas supplied to the town was very consistent. The water below would form a good seal without the need for rubber or any machinery. It’s a very simple, passive storage system.
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