working pressure of gas?

[Boyler]

hi lads,
i am fairly new to the scene but maybe someone can fill me in on why it must be recorded when there is more of a drop than 19mlb of working pressure,between the meter and appliance when the burner pressure is ok what "really" is the problem. if that makes sence

 

[Mbear]

hi lads,
i am fairly new to the scene but maybe someone can fill me in on why it must be recorded when there is more of a drop than 19mlb of working pressure,between the meter and appliance when the burner pressure is ok what "really" is the problem. if that makes sence

I always worked to the fact that 17mb working pressure was perfectly ok on most boilers unless the manufacturer species 19+mb is essential bud.

I'm not aware a reason to record 17/18mb working pressure?

 

[Blackcatgas]

Theoreticaly if you had a modern boiler with a zero governer connected to a large bag full of gas at 0 mbar the fan would suck the correct amount of gas through, (dont try that at home kids) I just tend to oversize the supply and make sure that the gas pressure is within what the mfrs want, the 1mbar drop over the installation isnt always achievable, for instance you can lose 2 mbar across the gas isolation valve inlet on a Vaillant.

 

[sparky]

Gas books say 21mb+-2 but if you read the MI's they will state what pressure they require. I nearly always install 28mm carcass and very rare see 1mm drop. as said, depends on boiler and where the inlet test reading is taken from before or after the gas valve.

 

[Puddle]

You can quite legallly have only 15m/b working pressure just after meter so if pressure not there in first place,does not matter what size pipework you put in to boiler,at best all you will do is transfer the 15m/b working pressure avalible to the boiler

These boiler manufactorers who insist on 19 m/b or even above, working pressure are working on the 21m/b +/-2,they are offically using the wrong figures,this figure is the legal requirement before the meter

They have no right officially requesting or designing a boiler that can not run to its required efficenciey on 14m/b in this country any working pressure over that is a bonus and of course most of the time a bigger working pressure is avalible,so not a problem however if it is,its down to you,as officially these boilers should not be fitted,as you should be fitting boilers that can operate under legal gas supply regulations and as said many are using the wrong figures
When you install these boilers you should advise the customer of this to cover your self and not get to upset if when you fit you can not reach manufactorers working pressure targets, no matter what the pipe size

I think manufactorers should also make this clearer,however in the desire to make smaller,bigger out put boilers,these fact get pushed to the back

But would add,the above shows why you should check avalible working pressure before you go fitting large output boilers,with promises of great hot water out put and heating range ,to find that is not the case,especially when maybe most needed during peak demands,like to have seen some of ther operation pressures during last winter

This siduation is being looked at now but the official out come,who knows

Maybe it will be like broadband were some areas will be given the official notice that boilers requireing higher working pressures can be fitted and the gas supply is gauranteed to be supplied and other areas,will have to wait for up grade or manufactorers will be told tough,go back to the drawing board and we remain with the had hock siduation we find our selves in now,we can not not fit them as someone else will and most of the time they will operate ok

But in the mean time be carefull,as if you fit a boiler and customer complains about output and manufactorers says requires bigger working pressure and gas supplier says tough,we are meeting our legal requirements ,were does that leave you

Please note, no one is saying these boilers are in anyway dangerous working on lower min legal gas supply but they will not meet their expected and advertised out puts
imho

 

[Billy Bob Bob]

puddles quite right on that one,a area i work in has very low working pressure between 16-17mb,so pipe sizing will make no difference if the pressures depleted in the first place the rule of 20mb =or- 1 is not achievable under those circumstances

 

[Boyler]

good god lads was not expecting those replys cheers. i never really seen the problem with it being arond 17mlb. just keep being told its not great to have it, especially on open flued appliances cause in summer when you record the pressure it is more than likely to drop more in winter with the wait it carries is that right?

 

[Bernie2]

Sounds a bit mixed up if you ask me. The external gas pressure on the utility companies mains are usually somewhere between 22Mb and upward, to a maximum well beyond domestic use.

The gas boards house meter inlet governor, is usually set at 20Mb with a 1Mb either way tolerance.

A boiler main burner may very well only require 10mbar but what does its pilot light require?

What about the simpler appliances that have no governor of their own, such as some gas fires, they rely on the pipeworks 20mbar inlet pressure to work properly using the injector orifice size as a passive regulator.
Although being fair there is usually some lee way. But 20mbar is a safety level.

If you have a lower inlet pressure the burner may not entrain enough air into the mix through the pre mix venturi tube, so increasing the chances of carbon monoxide occuring.

So its a case of getting your pipework sizes right and not allowing any old inlet pressure to be thought okay.

Its best to be safe than sorry.

 

[oldplumber]

b2 speaks the truth, and explains why the rules are there, cos not everybody has a nice new combi with a zero rated gas valve