Bladder tanks are usually supplied in one of two configurations and are used to reduce pressure surges in pipelines.
The air charge is contained within the bladder inside the tank. The air charge does not come into contact with the liquid in the tank and so cannot be absorbed. Air charge losses due to absorption are therefore not possibel as they have been eliminated.
The pumped liquid from the main flows into and out of the main tank, it will come into contact with the tank walls and so compatible materials must be selected.
The bladder is often made from a highly elastic rubber, such as butyl rubber, and may be sized to expand to fit the entire vessel. The bladder will typically be pre-charged at installation with a pre-determined pressure to give the correct operating level in the tank when the unit is connected to the main and at the operating pressure.
There must be an anti extrusion plate fixed at the outlet from the vessel to prevent the bladder from being drawn into the main at low pressures. The anti-extrusion plate and inlet size must be selected so that they do not impose a restriction on the flow into and out of the vessel, otherwise the unit will not function correctly as a surge tank.