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.

 

[crosbie]

My system is open vented.

I'm concerned that to avoid "Rise and fall to any degree" would require the use of a theodolite.

I suppose I could pass a run of transparent polythene hose down the intended route, fill it with fizzy fluorescent yellow Gatorade and see which end bubbles drift toward, and whether or not they coagulate into CO2 pockets (assuming the ability to inspect the full length).

However, it seems it would be easier if someone could authoritatively state that a rise & fall in pipework of an open vented system (with say 1m head, and a 5m head circulator) only leaves residual air pockets at h cm, and is not liable to cause an air lock until H cm.

Given such figures I would then have an idea as to just how careful I'd have to be - or not (preferably).

 

[Last Plumber]

There is no need to sarcastic !

I'm telling you my opinion on what you're asking. If you cant tell if a pipe is out of level without your polythene hose, perhaps you be better off getting a plumber in ?

There are reasons for not having high points.

If you do have them, you may ( as I already said ) get away with it. You may not.

Why don't you start the ball rolling by telling us how high H is ?

If you are running under a floor clipped to the joists for example, I wouldn't bother getting a spirit level out but I wouldn't go up and over the girder you mentioned without a vent !

Any air pocket on an open vented system could cause an issue.
There are no "this size of air lock is OK " tables.

 

[crosbie]

I agree that there's no need to be sarcastic (I intended none). I'm not here for a flame war, but for informed advice & opinion.

I agree that any air pocket could cause an issue, and that no size of air lock is ok.

It's at what height of rise & fall that these things occur that's the mystery. :-/

 

[crosbie]

[spurious duplicate]

 

[joni os]

Last Plumber has given a good answer. Water will take the course of least resistance around a circuit. In your case, resistance to flow through first rad will effect capacity to remove air from high point further along system. Good practice avoids high points or incorporates vents.
Theodolites will give both angle and elevation but are inappropriate for the task.

 

[crosbie]

Yes, good practice avoids high points, so in pursuit of good practice (and a lack of problems), I need to know what a 'high point' is in terms of rise & fall height, and how high a high point has to be that a vent should be incorporated where one occurs.

 

[Last Plumber]

I agree that there's no need to be sarcastic (I intended none). I'm not here for a flame war, but for informed advice & opinion.

I agree that any air pocket could cause an issue, and that no size of air lock is ok.

It's at what height of rise & fall that these things occur that's the mystery. :-/

I agree that there's no need to be sarcastic (I intended none). I'm not here for a flame war, but for informed advice & opinion.

I agree that any air pocket could cause an issue, and that no size of air lock is ok.

It's at what height of rise & fall that these things occur that's the mystery. :-/

There is no set height. Each system ( although a lot use the same design ) is unique.

They will all behave slightly differently.

Different rads/emitters, pipe sizes, the number of fittings and bends, lengths of tube, valves, boilers etc, all have differing flow rates and frictional resistances to contend with amongst many other things. Therefore, there is no "rule of thumb" for poor practice being acceptable. It's best not to try.

If it is not level or rising to a vent point, it will collect air/gas.

 

[joni os]

Shutting down rads. or back filling at mains pressure are both solutions to remove air and promote flow. How these are defined by "lack of problems".will relate to the definition you are seeking.

 

[crosbie]

Thanks for the tips. I knew about the mains filling one, but shutting down rads to maximise flow through certain parts of the circuit is a good one.

As to the key heights, unless someone with the requisite figures or formula posts them (eventually), I guess it may be a matter of setting up an outdoor experiment with a 2m high tank of coloured water, and transparent 15mm dia polythene pipe strung out over the ground with 'rises & falls' of varying heights. Then one can see at what heights air-pockets remain, and what height of rise & fall prevents flow entirely.

Place your bets...

 

[crosbie]

For the experiment, I should add that as the circuit is at 1m head pressure, then the supply tank (simulating a circulator of 5m head) would have to be at 3-3.5m and the end of the pipe would have to go up from the ground to a 1m high outflow.

 

[SimonG]

Thought this had been discussed on a previous thread?

 

[Last Plumber]

For the experiment, I should add that as the circuit is at 1m head pressure, then the supply tank (simulating a circulator of 5m head) would have to be at 3-3.5m and the end of the pipe would have to go up from the ground to a 1m high outflow.

You've misunderstood the concept entirely !

 

[SimonG]

Not a full deck. Must be some sort of engineer.

Sometimes things don't need over thinking.

 

[Best]

A waste of time. The system will work anyhow, unless you create serious high spots, although even then it probably will work.
As I said earlier, have a sealed heating system installed if possible, so that air will generally not be a problem once it is removed on any fill up.
Then install all pipework to give consideration for where the air can escape to, so as to do a reasonable job. If hard copper pipework can be installed, then have it done. But plastic plumbing or soft microbore copper have worked for years and still will do the job.
By the time you waste thinking about it, asking questions and experimenting, - you could have the job done properly and with best materials and methods

 

[jonnyswamp]

Knock yourself out fella
Just make sure you post your video on youtube and supply a link

 

[Dotty]

I think the point has been made now.

Thread closed.