Telford 18L Potable Expansion Vessel 19EXP - 434458

An expansion vessel is normally spherical in shape and contains a membrane or bladder. it will have a thread normally 1/2" or 3/4" MBSP on one end and on the other end there will be a Schrader valve which can be used for testing pressure or to re-instate the designated pressure required for the vessel. Potable Expansion Vessels are built from different materials than heating expansion vessels to ensure that the water is contaminant free and safe for human consumption. When fitted to an unvented cylinder the internal pressure of the vessel, is set to match that of the pressure reducing valve, which is determined by the set working pressure recommended by the cylinder manufacturer. Expansion vessels operate on the basis that the internal chamber is separated by a rubber membrane, inside this membrane sits the water and surrounding this sits a pocket of air. Water is a non-compressible substance so when it heats up it expands, the expansion vessel is designed to take up this additional volume of water (typically 4-6%) as the air pocket surrounding the membrane will compress to accommodate the additional volume of water. When the water inside the cylinder cools, the additional volume of water that was created from the expansion is forced back inside the cylinder by the air pressure contained within the expansion vessel that surrounds the membrane.