working pressure at meter

[AWheating]

its a grey area for sure, the last worcester i fitted i had a total drop from meter to gas valve inlets of 0.9mb (wp) in therory i could have allowed 2.5mb allowing for 1.5mb across the gas internals of the applaince. If i had a test point at the iso valve i could determine that any drop over 1mb was not all on pipework. I know of some engineers that will fit an test point before iso valve to allow correct measurements and peace of mind.

 

[Mike Jackson]

As far as I'm conerned it's quite clear for example Ideal state that the logic plus range is able to deliver it's full output at inlet pressures as low as 14mbar they also state that pipework should be fitted in accordance with BS 6891.

BS 6891 states

5.2.3 The pressure drop between the outlet of the meter and the points to be connected shall not exceed 1 mbar at maximum flow conditions.

This is not a case of MIs over riding British Standards but requiring that they are complied with. The low inlet pressures are not a get out for sloppy pipe sizing and installation but a safety net in case of low pressure problems with the supply.

 

[cascas]

This is the problem with manufactures stating low figures, some engineers will use this as an excuse to ignore undersized gas carcus. The best solution would be to include a test point at the isolation valve to ensure we can be sure we have got things correct.

Agreed. This is also suggested in gas safe bulitin re Worcester inlet pressure. The low pressures quoted do not mitigate the fact that only 1mbar loss is allowed over the pipework - the low figures are because the test point itself is causing a 1.5mbar loss, and therefore the supply to the appliance is actually correct,.

In theory in the event that pipework is undersized at what point would it start to affect flow rate/gas rate. I assume that as if gas demand is higher than the design limits of the pipework it will still be able to supply the required gas rate to the appliance and pressure would start to fall, until it got to the stage where the pressure was less than that required by the manufacturer before it would cause problems.

 

[cascas]

. .

 

[Leo21]

Ok, if the mi,s state a figure and there no way or no call for it from mi,s to put a test point in. Obviously you'll test with other appliances operating and anyone who adds an appliance is responsible for correct sizing up or down stream. Mi,s do some times over rule the regs, dfe fires for example over 7 kw need ventilation unless stated in the mi,s.

 

[AWheating]

yes i understand the argument about MI over riding the regs, but a gas carcus will in most situations have more than one appliance so cant be effected by any one appliances MI, and i think if you asked any manufacturer the opinion you will get the reply stating the same and pipework must comply to the current gas regs.

If they changed the regs then thats a different matter of course.

as reguards test point, my opinion is it would be helpful if manufactures fitted one. If on your gas safe inspection your inspector asked how do you prove the pipework has less than 1mb drop what answer would you give? a test point would help you prove this. But why would manufactures help us out??

 

[Leo21]

Fair one, gas regs are some times not as clear as they could and are open to interpretation . Be nice for some clear guide lines. Oh how it gives me a head ache deciphering it all.

 

[gasmarc]

yes someone should write a common sense book that we could all understand

 

[Brendan Rodgers]

The fact is it should be 19mlb min but if you make the call to get them to come and change thye gov. they may refuse as petty to them. Providing no appliances are effected and all burner and working presures are achieved dont worry about it..thats just my oppinion...
Bren.

 

[Leo21]

Speaking to one of the ESP guys the other day, and they've got a loophole they use. They say that in a situation where work is required to the mains as long as it's 6" in old money it's passable.

 

[cascas]

The fact is it should be 19mlb min but if you make the call to get them to come and change thye gov. they may refuse as petty to them. Providing no appliances are effected and all burner and working presures are achieved dont worry about it..thats just my oppinion...
Bren.

Am I right in my understanding that if working pressure if lower than the say 19mbar at meter, 18mbar at appliance, it will not affect the flow rate of gas available to the appliance? i.e 3m of 15mm pipe can supply 2.9m3/hr with a 1mbar drop. If length was longer (say WP showing a 2mbar drop) then 2.9m3/hr could still be delivered to the appliance?

 

[Brendan Rodgers]

It depends on the appliance but i dont know of one that it would affect,, AS PER VOKERA they have domestic modles that a dynamic gas presure as low as 12mlbr,, yes 12mlb is ok and wont affect its opperation..but thats only vokera, VAILLANT have told me they need 15mlb to opperate ok and 18mlb on WORCESTER..ITS DOWN TO THE MANUFACTURER...

Bren.

 

[AWheating]

Am I right in my understanding that if working pressure if lower than the say 19mbar at meter, 18mbar at appliance, it will not affect the flow rate of gas available to the appliance? i.e 3m of 15mm pipe can supply 2.9m3/hr with a 1mbar drop. If length was longer (say WP showing a 2mbar drop) then 2.9m3/hr could still be delivered to the appliance?

it depends on the type of appliance, hobs/cooker and gas fires normally rely on the correct pressures to operate correctly.

 

[gasmarc]

if the gas supply is not right you wont get the right flow rate and temperature from a combi. regardless of any manometer imho

 

[cascas]

but if calculated pipe size is ok, gas rate is not adjustable (zero govenor), OP inlet pressure is within spec, and gas rate within 10% of MI would you accept this gas rate as being close enough as acceptable

 

[Hobo128]

Sorry i was thinking standing pressure Between 19-30mb. Working Pressure 21 +or- 2mb
Call out transco for new governer.