Can anyone tell me, broadly speaking, what the symptoms of duff one of these would be? I'm referring to large metal tank, which presumably has a diaphragm in it, which supposed to be pressurised with air.
By "duff", I mean if the diaphragm is leaking, such that the unit had no air in it. Other than air in the system, what would be the effect of having no expansion room. Leaking joints and valves?
When the system heats up, the water expands. The expansion tank should accommodate this expansion, keeping the pressure rise down below approximately 0.5 bar.
If the expansion tank is totally blown, there is nowhere for the water to go. The pressure would rise rapidly, almost certainly operating the pressure relief valve (normaly at 3 bar or thereabouts). Lots of water would leave via the outlet.
When the system cools down, there would no longer be enough water to fill the system and the pressure would drop to zero + the head from the pressure gauge to the water level. This would require you to refill at the filling loop.
Sometimes, a system will have 2 expansion vessels. This is often the case with a large system, when the vessel internal to the boiler is insufficient to keep the pressure rise below 0.5 bar, so the designer has specified an additional vessel. In this case, the pressure rise upon heating may be excessive, but not enough to flow the pressure relief valve, as the working vessel works overtime.
Christian.
See below.
"Ed Sirett" wrote in news: snipped-for-privacy@makewrite.demon.co.uk:
A filling point. A pressure relief valve and discharge pipe. An expansion vessel A pressure gauge"
"Automatic air vent" should be one of these points.
Disappointed, I never went any further after that.
There is no requirement for an automatic air vent on a sealed pressurised primary circuit. Sure, they're very useful and labour saving, but many systems do not have them installed.
Christian.
The faq is great. Using it I upgraded to a sealed system with additional help from the group.
Also different manufacturers of expansion vessels give different locations for the vessel.
Also, while Googleing I came across Schnellkupplungen for a Membrandruckausdehnungsgefäß and what is involved is an item that enables the expansion vessel to be isolated for servicing without draining the whole system. Some contain a locking cap that is sealed in a similar manner to electricity and gas meters.
It seems that these conform to regulations in some parts of Europe, don't know about the UK.
It allows the vessel to be isolated from the system, water drained from vessel thus allowing the air pressure to be tested.
No doubt this thread will get the xenophobes going again.
Francis
A full bore valve before the pressure vessel does much the same thing. Turn off and remove.
I know few. if any, systems that do not require an auto air vent above the boiler on the flow pipe. In days gone by when there was no system boilers with integral pressure vessels and all components had to be external, an auto air-vent on the flow over the boiler was mandatory by all manufacturers. You didn't think, you just put one in.
I'm not saying they're not an excellent idea and extremely widely used, just that not all systems have them.
Christian.
Where components are not present in the boiler, it is common to use a sealed system kit, consisting of a manifold and the four items listed. These don't have a vent.
For a vent to be useful near to a boiler implies that there is a convenient place to install one and that the pipework reaches a high point immediately above it.
If the pipework is at the bottom of the boiler, then it should have an integral vent to be able to vent the heat exchanger.
Other than that, vents should obviously be at high points on the system.
.andy
To email, substitute .nospam with .gl
Although combis are invariably sealed systems and invariably contain an automatic air vent I did not consider that they were an _essential_ part of a sealed system.
Indeed so, and they do not need to be automatic. In my own home the highest points are the 4 upstairs radiators, the top of the indirect cylinder coil and the top of the boiler's heat exchanger. Only the latter has an auto vent. The others are manual.
pressurised
I would.
There is nothing to stop you writing your own superior FAQ with Answers on Sealed CH systems.
From my point of view a FAQ document is neither intended nor required to give information on every aspect of the subject. Indeed there is no mention in my FAQ on selecting the size of the vessel or precise adjustments for very tall systems (e.g. 5 storey town house.).
The FAQ has already made a dent in the number of postings on the subject, and freed up time effort for other more unusual questions to be discussed.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.