Confused about working pressure

[gas4you]

The 4mbar isn't lost by the network operator, it's inside the meter/governor/regulator

Chris; not doubting what you're saying but I am confused now

If the 4mBar is inside the meter/regulator etc. then how are we to know?

The test point is on the meter outlet so what we read here is all we need to know isn't it? This will always be adjusted to 21mBar +/- 2 at full load won't it

Apologies if I am missing something really basic and stupid

 

[baxpoti]

High efficiency boilers with zero gas governors (with or without offsets) can operate safely with a working pressure as low as 14mb at the appliance 21±2mb at the meter.

But you are still required to limit the pressure drop to 1 millibar.

Not according to some boilers M.I. !

 

[Agile]

Whilst some boilers are confirmed by the manufacturers as being able to work down to a low inlet pressure, thats only part of the story!

CORGI apply the British Standard recommendations of a maximum pressure loss of 1 mB as a requirement for all installations regardless of the requirements of the boiler.

The BS is not the law but CORGI require us to meet the BS for all of our installations.

Tony

 

[jonseyrs]

Whilst some boilers are confirmed by the manufacturers as being able to work down to a low inlet pressure, thats only part of the story!

CORGI apply the British Standard recommendations of a maximum pressure loss of 1 mB as a requirement for all installations regardless of the requirements of the boiler.

The BS is not the law but CORGI require us to meet the BS for all of our installations.

Tony

On numerous occasions I have enquired with Corgi about new condensing boiler installations half expecting a different answer every time and all of them have said the boiler working pressure must be within the tolerances of the manufacturers literature. So if a Vaillant is running full load at 17-25mbar working pressure on boiler gas inlet test point with all other appliances running its acceptable as the manufacturers literature specify that.

 

[baxpoti]

This normally leads to a heated debate..............

Extract from M.I.

12. After a period of 3 minutes and with all the system controls calling for heat, check that the gas pressure at the inlet tapping of the gas valve (Fig. 34) is greater than 14 mbar and the gas rate is no greater than 4.1m3/h.

Catalog » Baxi » Boiler » Combi (Condensing) » Combi 130 He (GC No. 4707504) » Installation Instructions » Baxi 130 HE iss 4

 

[baxpoti]

Ant101 your training notes will tell you that the working pressure at the meter is allowed to drop by 4mbar at full flow. That means that you can have 19mbar at very little flow, dropping to 15mbar at full load. Then a 1mbar drop in the pipework leaving you with 14mbar.

This is probably better explained in the Viper handbook ref J-3.

 

[ChrisR]

As the meter is owned by Transco, I include that in the network operator’s part.

Fair one, Ben!

The test point is on the meter outlet so what we read here is all we need to know isn't it? This will always be adjusted to 21mBar +/- 2 at full load won't it

No, that's the point, it isn't at full flow. It's at some vaguely specified flow like 3 burners...

Interesting point about the boiler MI. I suppose though that that doesn't mean you can install pipework which is NCS. So the pipework installation is "illegal" even if the boiler installation isn't! But if the pipe's already there...???
I'll call the dogs too, I wonder if they've changed their advice.

It applies to a Flowmatic I was about to change. It only sees 14mbar at its input flat out, and the pipework is buried in concrete, and really hard to replace. So could I stick a Baxi somethingorother in there? I don't know!! WP at the meter is 23mbar...

This is probably better explained in the Viper handbook ref J-3.

Very probably, but then I know what I mean, innit!

 

[taxexile]

the 3 ring test is very out dated now,i think this was based on a main london gas cooker.
saw a domestic range cooker yesterday and the 3 smallest burners will use double the amount of gas of the above cooker.
if only a cooker installed its a good test but what about electric cookers.the 3 ring test is not possible.
gas rates and makers instructions are the all inportant things now days,if gas rate correct with 14mb inlet pressure, corgi/hse and most gas engineers will not deam the boiler correct as per 1mb drop rule.
you gas guys must get this sorted out with corgi get them to update their testing method.ie condensing boilers reaching correct maximun gas rate with 14mb inlet should be passable.

 

[ollski]

Whilst some boilers are confirmed by the manufacturers as being able to work down to a low inlet pressure, thats only part of the story!

CORGI apply the British Standard recommendations of a maximum pressure loss of 1 mB as a requirement for all installations regardless of the requirements of the boiler.

The BS is not the law but CORGI require us to meet the BS for all of our installations.

Tony

But surely Tony as we have been told many, many times the manufacturers instructions take precident. Compartment ventilation is a BS but frequently overriden by MI's.

 

[ChrisR]

But surely Tony as we have been told many, many times the manufacturers instructions take precident. Compartment ventilation is a BS but frequently overriden by MI's.
__________________

Already answered that - the boiler mfrs cannot decree what the pressure drop in the pipe is.
Corgi do not decree what the inlet pressure of the boiler must be.
SO the boiler mfr is not overriding anything, he's just saying what his boiler will work with.
Obviously yes, there's a gap in the middle.

It's a bit like saying a car will do 120mph. It doesn't mean you're allowed to!

As we all know, a pipe pressure dropping from 21mbar to 14mbar could be dangerous for an unregulated app like a hob, which could go out.