guidance appreciated on general sytem operation

[idealmaint]

I recently went to a job on a newly installed combi boiler. Problems where that the boiler had lost a large amount of its pressure. The first thing i did was to check the pressure in the expansion vessel



When bleeding the upstairs rads there was a strong smell . I lit the "product" coming out of the bleed nipple in the upstairs rads and it turned out to be hydrogen

1.Now as i understand it hydrogen can be caused by either corrosion in the system or sludge (is this correct) y/n

2. My boss found a small leak on the system and explained that because the water contracts when it cools down it causes a vacuum and pulls air into the system.....He did say that i should completely forget about the hydrogen in the system and that the hydrogen is something thats not relavant. is it relevant and should i forget about it y/n

3. Is this creation of hydrogen only happening cause there is air in the system being pulled into the system via the leakin joint....y/n

4.or would hydrogen be caused without the introduction of air if the system y/n


5. as hydrogen is created do these gases increase the pressure and eventually force water out of the prv because as its generated the pressure increases . y/n



6. Is it more likely that a lack of inhibitor is the cause of this problem (i was told that the engineer did cleanse and put inhibitor in) y/n



7. Surely hydrogen is a sign that there is corrosion in the system or sludge which could lead to the premature demise of the boiler....Surely the cause should be rectified y/n

8. Does water that is lost in the system get replaced with an amount of air that takes up more space than the water (eventually operating prv) ...I thought the
air/hydrogen could be compressed much further than the water so the system would never over pressure in this way (because eventually u would get to a stage where there was little enough water in to operate pressure switch). Again on the baxi combi course i asked a question and was told that air in the system could force the system to become over pressurised temporarily and the prv to open and dump water


9.I also asked the question on baxi training course if a system over pressurised during operation would the prv operate and dump ALL the pressure contained in the boiler dropping the pressure to zero....the trainer said yes. My boss explained it differently and said what would happen was that the system would keep rising til the pressure got to 3.5 bar then dump the water til it got to 3.2 bar then stop there. Since when i got there the pressure was below 1/2 bar it could not have been a pressure issue but more so a leak on the system....Could anybody please clarify this point...who was right


10. Also if the boiler was overheating because of stat, THERMISTOR AND ot STAT failure then would also cause the boiler to dump water because water would boil and steam expands so quickly then in this instance you would expect the prv to open but this time dump a large amount of water out and when the system cools it would be well below the 3.2 you would see as described in the previously over pressure situation (ie hydrogen being produced in rads). y/n


again i have taken onboard and appreciate your comments. Hopefully this makes a much easier read and makes the question easier to answer. Ive got a head ache just trying to restructure it lol...and ive left loads off for another day

David

 

[Slugbabydotcom]

About this 200 words or less
Its still too long winded ....and a bit of a mess

If you give me some time I will now go through it
Cos true to my name I am as slow as ****

I think of these rhymes while I'm on the crapper
If you read this out right . You could be a rapper

Well it is POETS day after all!

 

[corgiman]

enmenslug next big thing

 

[idealmaint]

About this 200 words or less
Its still too long winded ....and a bit of a mess

If you give me some time I will now go through it
Cos true to my name I am as slow as s**t

I think of these rhymes while I'm on the crapper
If you read this out right . You could be a rapper

Well it is POETS day after all!

but pretty much all require one word answers

Its a good job q1ualified as an electrician first....english was never my thing at school I have tried getting this info from my boss but he is unhelpful. Theres about 10 engineers and over the past year 20 have packed in.

 

[chrishutt]

That's a bit better Dave, but still on the long side for this forum. To try to answer your points -

1. Hydrogen is formed as a result of corrosion. Sludge (iron oxides) is another product of corrosion.

2. Hydrogen generation is an important factor in assessing CH problems. A small leak could possibly result in air being sucked in, but there may be other explanations for the presence of air.

3. I think hydrogen can be formed without the presence of air, for example if a stray electric current causes electrolytic corrosion, but normally corrosion and hydrogen generation occurs when air is present.

4. See above, although I'm not sure about that.

5. Hydrogen, like any other gas, is easily compressed so it takes an awful lot to cause the system pressure to rise that much. I would have thought highly unlikely.

6. Lack of inhibitor would make corrosion more likely, but it is not the only factor. I don't think inhibitor can stop corrosion altogether if other factors are adverse.

7. Agreed.

8. Air will only enter the system if and where the system pressure falls below atmospheric pressure, typically on the inlet (suction) side of the pump. Therefore I can't see how air entering in that way could cause system pressure to rise so high.

9. If the PRV operates correctly, it would only open when pressure was above 3 Bar, but they often leak slightly after opening so it is possible for the pressure to continue dropping.

10. Sealed system boilers have safety devices to prevent them actually boiling, but if one did the pressure would rise and the PRV release excess pressure.

ive left loads off for another day

I'm off on holiday.....

 

[corgiman]

wow high turn over of blokes

not good


like slug I will have a look tomorrow, the stella has done its job tonight

 

[idealmaint]

lol cheers chris. Honst really appreciate your help. Ive deleted quite a bit more as you where writing this. Probably atleast 200 words from the beginning lol...but once again thanks.

It is a high turnover corgiman. ive never know a company like it. THANKS AGAIN Y'ALL

 

[Softus]

1.Now as i understand it hydrogen can be caused by either corrosion in the system or sludge (is this correct) y/n

Yes and no - both hydrogen AND sludge are the products of the corrosion process.

2. My boss found a small leak on the system and explained that because the water contracts when it cools down it causes a vacuum and pulls air into the system

Highly unlikely - the system will stop operating long before that degree of low pressure.

.....He did say that i should completely forget about the hydrogen in the system and that the hydrogen is something thats not relavant. is it relevant and should i forget about it y/n

It's a useful of confirming a theory that the system is corroding, therefore it's relevant, but not a problem that you can address on its own, which is probably why he said that you should forget it.

3. Is this creation of hydrogen only happening cause there is air in the system being pulled into the system via the leakin joint....y/n

Air in a system will hasten corrosion, but I don't know whether not air is being pulled in.

4.or would hydrogen be caused without the introduction of air if the system y/n

Yes - it is possible.

5. as hydrogen is created do these gases increase the pressure and eventually force water out of the prv because as its generated the pressure increases . y/n

No. The effect is usually to turn a radiator into a secondary expansion vessel, and lowers the pressure rather than raises it.

6. Is it more likely that a lack of inhibitor is the cause of this problem (i was told that the engineer did cleanse and put inhibitor in) y/n

Huh? If the system contained inhibitor then how can there be a lack of it? Notwithstanding that, if water is leaking out anywhere then the concentration of inhibitor will gradually be diluted as more water is added to the system.

7. Surely hydrogen is a sign that there is corrosion in the system or sludge which could lead to the premature demise of the boiler....Surely the cause should be rectified y/n

Yes.

8. Does water that is lost in the system get replaced with an amount of air that takes up more space than the water (eventually operating prv) ...I thought the
air/hydrogen could be compressed much further than the water so the system would never over pressure in this way (because eventually u would get to a stage where there was little enough water in to operate pressure switch).

Absolutely correct.

Again on the baxi combi course i asked a question and was told that air in the system could force the system to become over pressurised temporarily and the prv to open and dump water

This is a plausible theory.

9.I also asked the question on baxi training course if a system over pressurised during operation would the prv operate and dump ALL the pressure contained in the boiler dropping the pressure to zero....the trainer said yes.

The trainer was wrong - if the PRV is working correctly it will close again when the pressure reduces to below the maximum. If the PRV doesn't shut off, then the pressure could drop to zero.

My boss explained it differently and said what would happen was that the system would keep rising til the pressure got to 3.5 bar then dump the water til it got to 3.2 bar then stop there. Since when i got there the pressure was below 1/2 bar it could not have been a pressure issue but more so a leak on the system....Could anybody please clarify this point...who was right

Your boss is right, as long as the PRV behaves itself. The problem is that most of them don't.

10. Also if the boiler was overheating because of stat, THERMISTOR AND ot STAT failure then would also cause the boiler to dump water because water would boil and steam expands so quickly then in this instance you would expect the prv to open but this time dump a large amount of water out and when the system cools it would be well below the 3.2 you would see as described in the previously over pressure situation (ie hydrogen being produced in rads). y/n

Blimey! But isn't this just a repeat of the previous question?

 

[Slugbabydotcom]

Well in tortoise and hare fashion heres my take on it:-

1.Now as i understand it hydrogen can be caused by either corrosion in the system or sludge (is this correct) y/n

Corrosion in the system
The Hydrogen escapes in the production of the sludge

2. My boss found a small leak on the system and explained that because the water contracts when it cools down it causes a vacuum and pulls air into the system.....He did say that i should completely forget about the hydrogen in the system and that the hydrogen is something thats not relavant. is it relevant and should i forget about it y/n

Forget about it for now Yes Hydrogen is a problem that should be attended to but it's slower acting than you seem to suggest

3. Is this creation of hydrogen only happening cause there is air in the system being pulled into the system via the leakin joint....y/n

No the Hydrogen is a by product of the electrolytic action that is going on between the disimilar metals in the system

4.or would hydrogen be caused without the introduction of air if the system y/n

Yes In the water there are 2 atoms of hydrogen to every one oxygen. While the oxygen goes off to make oxides the Hydrogen has no friends and reverts to its gaseous form

5. as hydrogen is created do these gases increase the pressure and eventually force water out of the prv because as its generated the pressure increases . y/n

It's possible I suppose but only over a long period of time. Experience teaches you that generally it is to be ignored in relation to the way you have posted this question

6. Is it more likely that a lack of inhibitor is the cause of this problem (i was told that the engineer did cleanse and put inhibitor in) y/n

I missed this one out but see Softus ' version above that's more or less what I would have said

7. Surely hydrogen is a sign that there is corrosion in the system or sludge which could lead to the premature demise of the boiler....Surely the cause should be rectified y/n

Yes

8. Does water that is lost in the system get replaced with an amount of air that takes up more space than the water (eventually operating prv) ...I thought the
air/hydrogen could be compressed much further than the water so the system would never over pressure in this way (because eventually u would get to a stage where there was little enough water in to operate pressure switch). Again on the baxi combi course i asked a question and was told that air in the system could force the system to become over pressurised temporarily and the prv to open and dump water

Hydrogen is a gas and it compresses unlike a liquid so it would be acting as more pressure vessel space until you let it out then the pressure would drop

9.I also asked the question on baxi training course if a system over pressurised during operation would the prv operate and dump ALL the pressure contained in the boiler dropping the pressure to zero....the trainer said yes. My boss explained it differently and said what would happen was that the system would keep rising til the pressure got to 3.5 bar then dump the water til it got to 3.2 bar then stop there. Since when i got there the pressure was below 1/2 bar it could not have been a pressure issue but more so a leak on the system....Could anybody please clarify this point...who was right

Your boss is right however the 3.2 is arbitrary I have seen them not stop till they got down to about 2.7 They are supposed to stop at 3 but at that pressure whats half a bar between friends

10. Also if the boiler was overheating because of stat, THERMISTOR AND ot STAT failure then would also cause the boiler to dump water because water would boil and steam expands so quickly then in this instance you would expect the prv to open but this time dump a large amount of water out and when the system cools it would be well below the 3.2 you would see as described in the previously over pressure situation (ie hydrogen being produced in rads). y/n

PRV's can blow in a overheat situation but is it overheating?

Rather than all these questions and suppositions, would it be possible for you to SIMPLY STATE WHAT IS GOING ON?

Ok in general yes there is a hydrogen problem and it should be attended to. More urgently than that you need to find out why its losing its pressure.
I suggest either a leak in the pipework or from the PRV
or perhaps a pressure vessel that is the culprit.

With the system cold and at 1 bar does the pressure rise to over 3 bar and then blow out when you run the system? If so it is indeed the pressure vessel

Does the PRV drip before the 3 bar is reached ?
If so it is the PRV

Is the automatic air vent leaking?

What make is the boiler?

Is there a leak ? The worst kind is the leak thats under an expensive newly laid laminate floor. Usually where dampness copper and concrete happen to be in the same place. Ahain due to electrolytic action

Read THIS before you post again It lays out a procedure that has been tested on this site for some time about how to pose your questions

 

[Softus]

In the water there are 2 atoms of hydrogen to every one oxygen. While the oxygen goes off to make oxides the Hydrogen has no friends and reverts to its gaseous form

sbdc - this is not wholly correct, because there are free oxygen atoms held in solution in the water, and these are gobbled up in the corrosion, hence quite often the volume of hydrogen produced is low or nil.

Rather than all these questions and suppositions, would it be possible for you to SIMPLY STATE WHAT IS GOING ON?

Hear hear!

 

[croydoncorgi]

Hydrogen can be caused by electrolytic action involving dissimilar metals but also by bacterial action. Most / many corrosion inhibitors claim to inhibit bacteria as well as corrosion.

 

[idealmaint]

Rather than all these questions and suppositions, would it be possible for you to SIMPLY STATE WHAT IS GOING ON?

The reason so many questions was that i was simply (ok maybe not so simply) trying to get a proper understanding how certain things work. It is really hard to communicate something when you dont really fully understand (but want to, hence the time spent researching etc).

I know guys that have been doing this 20 years but they have no where near the understanding that the people who have kindly replied to this thread do have. Hence me asking questions on here rather than elsewhere

Again my questions/original 60 page novel werent aimed at fixing one particular problem more so they where to help me gain a deep understanding so that in time maybe i can class myself as an expert in this field rather than someone who just gets by

My questions shall be a little clearer in future. Just got up but was so happy with the responses that i got thought i must thank you all now. Will re-read again later. Any future topics shall be in the format suggested by the link previously offered

Thanks again

 

[chrishutt]

.... i was simply (ok maybe not so simply) trying to get a proper understanding how certain things work.

Dave, if you'd said that in the first place I think we would have approached this differently. Several people spent a lot of time going through your detailed post and compiling careful responses, thinking that this was leading to the resolution of a particular problem. But you now say you just wanted to get some general background knowledge!

Had we known, we might have referred you to existing sources of background information. For a start, the FAQ topic now has a wealth of information, also carefully compiled by people from this forum. In addition there is an even greater wealth of info. in old threads on this forum which you should be able to access via the search facility (if it's working?).

As you have discovered, there are quite a few of us on this forum who are willing and able to give sound advice and guidance to others, but, in fairness to us, you need to be a bit clearer about what you're really trying to find out. For example if you want to find general information on the chemistry of corrosion, just say so and we will try to point you in the right direction.

 

[idealmaint]

sorry double post see below

 

[idealmaint]

a good point chris. ...which is exactly what i meant. Thanks again everybody for your input I shall definately try and think things through a little better. If anybody knows of any literature i could purchase to assist me in my search for knowledge on the chemistry of corrosion i would indeed be grateful