An unvented hot water cylinder is fitted in a home to sore the water that is supplied straight from the mains water feed, and the it heats it by the use of either an electrical heating element (immersion heater) or with heat provided by a boiler. These cylinders give high pressure hot water supplies that supply outlets with a high pressure flow of hot water. Hampstead Plumbers are trained on all types of cylinders. The pressure under which these cylinders store water is quite high, usually in the region of 2-3 bar, and because of this are able supply water to outlets that are fitted high up in the home, like a loft space, with similar pressures to the mains cold water supply. This high pressure also makes for better and stronger shower experience, with no need to fit a pump.Because both hot and cold water services are supplied from the mains, there is no need for a cold water storage tank, which keeps the loft clear, and reduces the pipework. A Hampstead Plumber can fit a cylinder.

Expansion.These vessels need to allow for the expansion of the water inside as it heats up, and makers usually use one of two methods:External Expansion Vessel.
The expansion vessel is just a trapped volume of pressurised air, that is held with a rubber diaphragm inside a steel vessel. This vessel connects by pipework to the unvented cylinder, normally on the mains cold inlet pipe, and as water in the cylinder expands it is forced into the expansion vessel, which in turn compresses the air in the diaphragm. As the air compresses, both, its pressure, and the water pressure in the cylinder increases. Thet bigger the expansion vessel, and the smaller the pressure increase. Normally, the vessel charge pressure should be 0.2 bar below the pressure reducing valve setting.

Internal Air Bubble.
There is another way to accommodate the expansion, and that is to trap a bubble of air inside the top of the cylinder. This bubble compresses as the water expands, just like air in an expansion vessel. This is a simpler design, with no need for to fit or ever replace an expansion vessel, but annual servicing of the cylinder is recommended to keep the bubble and stop safety discharges from happening.
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