Gravity hot water to fully pumped / sealed

[SJB060685]

leave the f and e tank in so it will stay the same pressure

sealing could cause issues with leaking on joints etc if in a concrete floor

But the vent is on flow of HW, not only will this pump over when calling for HW but the vent is not open if valve is shut?

 

[eagleeye]

If you leave the vent as is then whenever HW is called for it will pump over, in time it will sludge up the system. Im assuming Shaun is suggesting seal the system and do away with f and e tank, which is what I would suggest. Preferably the expansion vessel will go on return where it’s not exposed to high temperatures, if the pump is on return the vessel should be close to suction inlet of pump to maintain a positive pressure through boiler and around the system, thus eliminating any air ingress.

Thats what I thought. Think I will fit the vessel above the boiler on the return, remove the f + e tank and fit AAV's on what used to be the feed and vent. At least this way the coil can release trapped air
[automerge]1578097374[/automerge]

leave the f and e tank in so it will stay the same pressure

sealing could cause issues with leaking on joints etc if in a concrete floor

[automerge]1578097473[/automerge]

leave the f and e tank in so it will stay the same pressure

sealing could cause issues with leaking on joints etc if in a concrete floor

Would love to but cant see how im goona get over the airlock issue. This way I can fit AAV's on the old feed and vent pipe once i remove the tank

 

[ShaunCorbs]

But the vent is on flow of HW, not only will this pump over when calling for HW but the vent is not open if valve is shut?

will have a 2 bar blow off on the end of it so no pumping over
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Air lock issue ??

 

[SJB060685]

Yes I see what you're suggesting Shaun. How many systems have you known to be configured like this, personally I wouldn't feel comfortable

 

[ShaunCorbs]

I’ve done one to date couldn’t seal due to pipework and not enough pressure

worked ok and no complaints so far been in 2 years

 

[John.g]

In case of any worries re pressurising the system (old pipework etc) it might be no harm adding that the E.vessel should have its pre pressure reduced to whatever the static head is and be as large as comfortably possible , that way the final pressure will still be very very low, probably < 1 bar with hot system.

 

[SJB060685]

I agree with John to a degree. The expansion vessel pre charge should be set higher than the static head at that point. The system should be then be pressurised to roughly .2 bar higher. Yes a larger expansion vessel is not a problem but one you're tight for space and two theres no point spending additional money on a 50 litre if a 12 is enough. You need to calculate the vessel volume required using system volume etc. Like I said ideally you want the vessel on the return, tapped in just before pump inlet, this will give the neutral point at that tap in, negative pressure in short piece of pipe before pump and then positive pressure through boiler and rest of system back to neutral point, thus eliminating possibility of air ingress.

 

[John.g]

I wouldn't like to see the EV pre pressure < 0.4 bar in case it doesn't push the diaphragm up against the opposite end, and because you will always have "auto filling" via the F&E tank then there is no need for a EV water reserve so Pre & filling pressure in these systems can be the same IMO, assuming system volume of 100 litres and a mean boiler temperature of 75C and assuming a static head of 4M with a 12 litre EV then the maximum system pressure will still only be 0.76 bar when hot. If one "forgot" to reduce the pre pressure then 1.0 pre pressure will result in a final pressure of 1.52 bar and 1.5 pre pressure will result in a final pressure of 2.15 bar.
Bord Gais approved RGIs here have installed literally "tens" of these systems near me on converting from oil to gas with no problems whatsoever, they use(d) swing check NR valves (which have to be installed in the horizonal) rather than the poppet type.

 

[SJB060685]

John where are you getting this info to calculate the vessel charge and system pressure when hot? It seems to be more in depth than what I have in front of me, can you supply a link?

 

[John.g]

I just work(ed) it out from first principles many years ago when I was involved in industrial pressure vessels, boilers etc, you (or anyone) can input your own numbers here.