Nitrogen, a dry inert gas used in the Reflex range of expansion vessels, improves the vessel’s life span by reducing corrosion inside the vessel, and prevents loss of pre-charge pressure. Nitrogen permeates through rubber slower than oxygen, is far less reactive to both steel and aluminium and does not degrade rubber prolonging the membrane life. Oxygen in compressed air permeates through the membrane, thus reducing the pre-charge pressure over time. During normal operation, oxygen oxidises the membrane in the vessel, causing under-inflation, but dry nitrogen will maintain proper inflation pressure and will not corrode the inside of the vessel.