ideal logic/independent c 30 inlet working pressure

[darren bastin]

i have been reading various threads about apparant pressure loss when measured on the gas valve ( underneath the boiler nr yellow lever). I have not managed to get more than 19 mb despite oversizing the gas pipes. thought that at some time i would get banged up in prison for this.

Do I understand this right 21 mb at meter , 1mb allowed loss and 1.5 mb across the valve , so 18.5 mb is spot on when on max with every other gas appliance running.
If this is the case at what stage would you have a problem with a gassafe inspection. Are we saying that 14 mb at the gas valve(lever) but gas rate witin tolerence and gassafe are happy? Cant understand why the gas connection cant be 22mm as i take 22mm to within one 15mm m and f to the boiler.
Clarification please

 

[GrahamM]

If you read the regulations/standards and the various threads you will know that you can have a WP of 19 MB at meter. 1 MB drop across pipework and potentially 1.5 MB drop to gas valve inlet test point.

So the resulting WP at the appliance may be as low as 16.5 MB if the manufacturer permits and all checks are sound.

 

[darren bastin]

Thanks Graham M you confirm what I thought for the first part of my question. However as regards to the second part I am still unsure, the MI state(I think) that full gas rate can be acheived as low as 14 mb on this boiler, this seems to be at odds with other rules. So how would an installation be classed , in the past when I have come across wp as low as 12mb gassafe has said providing the wp is above the max bp the boiler is ncs. With a forced draught boiler there is no bp so how would this be classed. Sorry to labour this point , but can any of you experienced knowledgeable blokes nail this for me .

 

[quality]

It's better to remove the screw completely from the test nipple to get a proper reading

 

[Hardy1]

Thanks Graham M you confirm what I thought for the first part of my question. However as regards to the second part ''I am still unsure, the MI state(I think) that full gas rate can be acheived as low as 14 mb on this boiler,'' this seems to be at odds with other rules. So how would an installation be classed , in the past when I have come across wp as low as 12mb gassafe has said providing the wp is above the max bp the boiler is ncs. With a forced draught boiler there is no bp so how would this be classed. Sorry to labour this point , but can any of you experienced knowledgeable blokes nail this for me .

gas rate!!= 14mbar????????????????????????????, confusing me there when im reading that????

 

[cascas]

I have had the same issue with the logic range. 21mbar at the meter, and just over 18.5 at the test point. After discussion with Ideal they have confirmed that test work has proven that the pressure drop is directly proportional to the flow rate through the valve, and have quoted a 1.8mbar drop for the 30kw. If your meter pressure is 21, and you are showing 18.5 OP at the test point, then yo u have a 2.5mbar drop, 1.8 of this is attributable to the test point, so your pipework drop is only 0.7, well within spec.

20.3 mbar is being supplied to the boiler - it is just that the test point give a low reading. Have you gas rated? what are your readings. I have found the logics to rate on the low side.

See graph below.

 

[darren bastin]

When gas rated the boiler consumes 1 foot of gas in 34 seconds 32.29 kw gross 29.09 kw net. So its pretty close. I have to say all the ones I have fitted have tended to be under the stated value but only marginally. With regards to the MI i am struggling to understand how the boiler could work down to 14 mb and perform at full gas rate?

 

[Mike Jackson]

All manufacturers quote the 14 mbar now. I'm sure it's something to do with EU regs that they have to work safely down to that pressure.

I had a Worcester 24ri working with a working at the meter of 3 mbar last year, didn't bother to check working at the boiler until after we'd had a new meter governer fitted.

 

[cascas]

When gas rated the boiler consumes 1 foot of gas in 34 seconds 32.29 kw gross 29.09 kw net. So its pretty close. I have to say all the ones I have fitted have tended to be under the stated value but only marginally. With regards to the MI i am struggling to understand how the boiler could work down to 14 mb and perform at full gas rate?

I struggled to get my head round this. Assume that pipework is undersized. The boiler will still run and burn 3m3/hr but as the pipework is undersized the pressure will fall at this demand level, if pipework was further undersized then pressure would continue to fall until lower than 14mbar, where the boiler may start to have combustion issues.

If pipework size is increased, the OP supplied to the boiler will increase, but it will not change the amount of gas used by the appliance.

In anycase, the pressure drop over the pipework should be no more than 1mbar from the meter tho meet BS. Assuming the meter supplies 19mbar, then the lowest OP at the test valve should be 16.2mbar (19mbar meter, 18mbar at pipework, 1.8mbar lost in test point valve)