Maximum deviation from horizontal before air lock?

[crosbie]

In a pumped radiator circuit, in long horizontal-ish stretches of pipework (say 15mm dia), what's the maximum typical rise/fall before air pockets become persistent (aren't moved on by pumped flow) and cause noise/gurgling, and before air locks prevent flow?

Apologies if this is a common query, but I've not figured out how to phrase the question such that I can get an answer via Google.

I'm expecting that it's something like >3-9cm for air pockets to persist, and >10-30cm for air locks to occur.

I appreciate it can depend upon the pump...

I'm considering the use of soft copper pipe, manually unwound from coils, which can end up being a bit wiggly, and moreover, I can't be sure the successive floors it'll be going along are all exactly the same height (and this is without intervening radiators to capture stray air).

 

[crosbie]

For example, lets say there's a 10m stretch between two radiators, and the supply pipe is perfectly level, but for the need to temporarily rise H cm halfway between the two rads in order to avoid something (a steel girder say). Assume a circulation pump of 5m head (and consider that it regularly reaches full speed/power).

At what values of H cm would you:

a) Not worry.
b) Consider the possibility of air-pockets/gurgling, but likely to be tolerable.
c) Install an automatic de-aerator just downstream of the high point - just in case.
d) Bet that an air-lock would occur, and a de-aerator is a must.
e) Go back to the drawing board, e.g. re-route pipework.

Being largely uninformed about this, I'd hazard 3/5/10/30/50, but I'm very interested in rules of thumb, other people's hunches, scientifically determined values, 'common knowledge among qualified professionals', etc.

 

[Best]

Truth is, on pumped circuits you could nearly get away with pipes having high spots anyhow.
A few facts are - on horizontal pipe runs there will be no problem with air if you have a point for air to go into, like a radiator, at one or both ends. People have been installing 8 and 10mm microbore copper plus flexible plastic plumbing for years and get away with air problems eventually.
You really shouldn't have constant air in a heating system - especially if it is a sealed system which is much preferable if gas or oil system.
I would rather have hard copper pipework, 15mm to rads, coming from 22mm or 28mm and all the pipework to be installed to consider the air escaping easily on any fill up.

 

[SimonG]

I wouldn't give it a thought on a pumped circuit.

 

[jonnyswamp]

Are you trying to design/install a large system
A level pipe will be fine between 2 rads even at 30ft, but how large is the system?
Is this a hypothetical question

 

[crosbie]

I know a level pipe will be fine, even at 30m. The hypothetical question (that influences how careful I'll be when it comes to installation) is what height of bump in the pipe ceases to be negligible and potentially can become a problem.

 

[Last Plumber]

The good pipe rule !

You can fall and rise to a vent point but never rise and fall.

Domestic Heating pumps are not pumps, they are circulators.

They won't always shift air pockets, especially on an open vented system.

If it's sealed, the fact that the pressure can be raised will help to slightly compress the air pocket and make it easier for the pump to shift it, as long as it ( air ),isn't in the pump of course.

My advice is to always avoid high points without vents. I would also advise you use manual vents as opposed to automatic.

 

[crosbie]

Thanks, but it's how one defines 'rise & fall' or how high a 'high point' is that concerns me.

Is a 'rise & fall', a brief change in height of 1mm? 1cm? 10cm? What?

As to automatic vents, I was assuming they'd be appropriate if a high point was in an awkward location.

 

[Last Plumber]

Thanks, but it's how one defines 'rise & fall' or how high a 'high point' is that concerns me.

Is a 'rise & fall', a brief change in height of 1mm? 1cm? 10cm? What?

As to automatic vents, I was assuming they'd be appropriate if a high point was in an awkward location.

I can only give you my opinion on AAV's from my own experience.
They tend to leak eventually if a system is dirty. ( even mildly). Manual vents are closed after use and checked for leaks.

If a system is installed correctly and has clean water and inhibitor in, it it should not collect any Air or Hydrogen and therefore should not need constant venting. Once it's full, it should stay full.

As far as rise goes, I have always avoided it. So when installing Heating pipe work, it should always have a slight rise to a vent point, such as, The open vent, Radiators, Air vents etc.

It is possible of course that you could rise and fall with a Heating pipe without a vent and get away with it, as I said earlier, particularly on a modern sealed system.

I personally still wouldn't do it !

Is your system open vented ?

If it is, I would not advise you to rise and fall to any degree without a manual vent at the highest point of that rise.

 

[Last Plumber]

Thanks, but it's how one defines 'rise & fall' or how high a 'high point' is that concerns me.

Is a 'rise & fall', a brief change in height of 1mm? 1cm? 10cm? What?

As to automatic vents, I was assuming they'd be appropriate if a high point was in an awkward location.

I can only give you my opinion on AAV's from my own experience.
They tend to leak eventually if a system is dirty. ( even mildly). Manual vents are closed after use and checked for leaks.

If a system is installed correctly and has clean water and inhibitor in, it it should not collect any Air or Hydrogen and therefore should not need constant venting. Once it's full, it should stay full.

As far as rise goes, I have always avoided it. So when installing Heating pipe work, it should always have a slight rise to a vent point, such as, The open vent, Radiators, Air vents etc.

It is possible of course that you could rise and fall with a Heating pipe without a vent and get away with it, as I said earlier, particularly on a modern sealed system.

I personally still wouldn't do it !

Is your system open vented ?

If it is, I would not advise you to rise and fall to any degree without a manual vent at the highest point of that rise.