Thanks to GasGuru
If you are contemplating an unvented cylinder installation, you should
always check the static/dynamic incoming water pressure and flowrates first. Be aware some street pressures drop considerably at peak times i.e. test at this time to avoid disappointment.
There are two basic types of cylinder, air bubble (bubble tops) e.g. the Megaflo and those having a separate expansion vessel. Some external vessels are however hidden within the top casing of the cylinder.
The pressure reducing valve does not necessarily need to be installed alongside the cylinder..sometimes it is more convenient to place it under the kitchen sink.
It is always worth fitting a pressure gauge into the reducing valve (they normally have a blanked port) to enable the set pressure to be checked on a regular basis. The gauge is also useful to indicate blocked inlet strainers or insufficient water supply problems.
Unvented cylinders must be maintained on a regular basis (normally annual). The bubble must be re-generated or the expansion vessel pre-charge pressure checked (and re-inflated where necessary).
Strainers, PRV setting etc should also be checked. Failure to service on a regular basis will lead to safety device activation leading to expensive repair costs. Manufacturers warranties are also invalid without a signed service schedule.
A 2 port zone must be used if connecting the cylinder to a conventional boiler. Solid fuel boilers must not be connected directly to an unvented cylinder.
Eg Here
