Gases are sometimes stored in tanks which is called gas holders. Its structure is such that a cylindrical chamber that is open on one side and is placed vertically inside a tank of full of water or another fluid. The placement should be such that the closed side of this cylindrical chamber is at the top and the open side is at the bottom.

The boundary between the two walls and between the cylindrical chamber and the tank of full of water forms the sealing part. As the gas enters the cylindrical chamber and accumulates in it, the chamber moves and rises inside the full of water tank and the gas is kept in the space of cylindrical shape and water.

Welded Rails to the wall of the cylindrical chamber are used to maintain the balance of the cylindrical chamber as it ascends and descends. These rails go up and down inside the wheels connected to the full of water tank. In order to prevent the cylindrical chamber from rising too high or from hitting the bottom of the water tank, retainers are used at the top and bottom of the water tank that are attached to the wall.

 VCM storage tank ( Gas Holders ) in Bandar  Imam Petrochemical Complex PVC unit is an example of such tanks