Arranging CH pipes and auto-air bleeding

[Tim Watts]

My CH will be a bit of a hassle WRT to airlocks - as I have a solid ground floor so all CH pipes will drop down to rads, the boiler and the cylinder from the first floor (also the roof as it is a dormer bungalow).

The pipe run I have in mind will be two perimeter legs about 18" above first floor level, the highest point in the system other than the header tank (ys, it will be a vented system).

Thus it would be an obvious point to incude bleeding valves or air removal traps on these legs, close to the final drop back to the cylinder (this will be a heatbank type system, so rads plumb directly to bulk of water in cylinder).

Is there any way to use a three port air trap chamber:

18638 et al) in these legs, with the air vent pipe looping up and into the top of the header tank?

Done wrong, it is obvious that pump pressure will cause it to pump over.

Is there a "right way", such as in the return leg where I assume the pressure will be lower.

Or is there a more magic device - I don't know what those other parts on the same BES page are, eg Aerjec, Spirotech are - never seen those before...

By default, I was going to incorporate a manual bleed valve on the high legs, but wondered if there was an elegant automatic solution that would work with only a small head between the pipe and the tank?

Just curious...

Cheers

Tim

[dom]

Pumping over shouldn't be a problem for a thermal store - all pumping is from/to the store - and the F&E tank goes into a separate feed to the store.

Be sure to install a drain-off tap with every radiator, if they drop separately from the high-level circulation pipework.

You might find it's easier to reverse fill the system through these too.

I spent a chunk of time juggling my pipework layout and the height of the platform for the cylinder to almost totally avoid height offsets on the radiator (and boiler) circulation pipework.

As far as air bleed valves, I installed one of these:

the one point in my system where I had to route a down-leg before a pipe returned to the cylinder - in practice it accumulates little or no air, and I can fully bleed the system by going round each rad once.

You might find likewise - if you can keep your circulation pipes level, or slightly sloping upwards, that air will find it's way to the store/cylinder and out via the vent-pipe.

I wasn't able to use one, but combined stores with F&E tanks look to be one less hassle.

[Tim Watts]

[e-mail] ( [e-mail]) wibbled on Wednesday 09 March 2011 07:44:

Hi Dom,

Yes - I can see that :)

I should note that my store/cylinder is also on the ground floor (weight) so it will belled itself OK via the expansion pipe, but not so well the 2 distribution legs that are 1m above the top of the store.

Sorry - I didn't make that clear.

I suspect the odd bubble of air would get pused down into the cylinder OK by normal water flow (to then find its way back to the expansion/vent pipe).

But I suspect significant air in the legs will lock the system. So I'm pretty sure I will need to bleed the 2 legs, but was wondering if an air seperator would work. What sort of pressures are developed by a CH pump (in metres head of water?)

That was my default choice too - not fully auto (in that you should lock it down for normal use) but it would be good for the initial setup where it could be left open for a few days until the dissoved air is out).

Agree - slight slope back to a convenient point to put the bleed valves.

Indeed - though not an option. Due to the cranky loft layout I'm struggling to get much head on the expansion tank...

Cheers

Tim

[dom]

I suspect you will have a good pay-off in improved air expulsion, for an extra height you can get.

As far as head generated by domestic circulation pumps, IIRC it's more like 150-300mm of head, depending on your pipe layout/size/flow- restrictions/etc and pump speed.

Grundfos publish graphs for guidance on their website.

There's a formula in Treloar on plumbing for calculating the necessary height over the F&E tank for the vent pipe - can't recall it offhand.

[Dave Plowman (News)]

I can't think of any benefits in a new open system over sealed. But plenty of disadvantages.

[Tim Watts]

Dave Plowman (News) ( [e-mail]) wibbled on Wednesday 09 March

2011 11:14:

Maybe - but the advantages are for me:

a) I understand open vented generally (ie I don't have to worry about blowing stuff up)

b) With a thermal store where the bulk of the CH water is in the tank, not a coil, it would cost more to have a pressure rated cylinder over what is basically a modified with extra tappings copper cylinder...

[Tim Watts]

[e-mail] ( [e-mail]) wibbled on Wednesday 09 March 2011 11:03:

Hmm - 300mm (yes I will look up the pump charts) but I think I can arrange to have that plus a margin. I can take the exansion vent pipes right up into the crook of the roof then drop back down into the top of the tank to get extra height on the leg.

Ta

Tim

[ARWadsworth]

Told you to go sealed system:-)