1mb Drop on all existing pipework, Pipesizing Question.

[cmarkr]

Hi all, Firstly i feel really dumb asking such a amateurish question so please be nice as i feel i have to ask for clarification i'm working correctly. Two resent conversations with an ex gsr installer i work with and my old mentor have suggested i'm doing this wrong.

Currently when replacing an appliance in a house for this example we'll use a gas fire replacement (in this house there is also a gas hob and a boiler). My understanding is that i'm connecting to an old supply and i have to ensure i have a no more than a 1mb drop with all other appliances on.

My Method 1.My normal procedure is connect a manometer to the meter outlet test point and light the fire i've just fitted. This will give me my meter working pressure say at 21mbar, i then check my other manometer to the fire and it says 20.5mbar. So far so good. I would then fire all four rings on the hob and run the boiler at maximum output. Once everything is running and then re check the manometer connect to the fire if it shows 20mbar or higher. Jobs good happy days................. Is my current working method correct?

Ex Mentors Method 2.He said that i only have to do this test with only one other appliance running (the next highest Kw rated appliance).
So his method would be for example in this scenario; attach a manometer to the meter outlet test point and light the fire he's just fitted. This will give him a meter working pressure say at 21mbar, he then check's his other manometer to the fire and it says 20.5mbar. So far so good. He would then just fire up the boiler on maximum neglecting theirs a hob fitted (hob remains off), the recheck at the fire the working pressure. Is his working method correct?

Ex GSR Method 3.He has suggested that you are only looking at the pressure in immediate connecting pipe between the meter and the appliance you've just installed.
So his method would be for example in this scenario; attach a manometer to the meter outlet test point and light the fire he's just fitted. This will give him a meter working pressure say at 21mbar, he then check's his other manometer to the fire and it says 20.5mbar. Happy days, forget theirs a hob and a boiler on the other leg of the gas pipe and if he measured and he was say 19mbar he would just be upgrading the immediate leg between the meter and the fire and leave the other leg feeding the boiler and hob untouched. Is his working method correct?


This is all doing my head in ive spent all last night and this morning pulling out all my literature from my exams and all sorts and cannot find a stable answer, in one of my bits of literature it states: 1mbar is the maximum acceptable pressure drop on natural gas installation between the gas meter and the furthest appliance away running at maximum demand. So this note suggests that as long as the furthest appliance away has less than 1mb drop with nothing else running its all good just start banging in appliances before this point.

Any help would be great as i normally work on LPG were pipesizing is more lenient and this is becoming very stressful for me to understand, Thanks very much in advance

 

[Deleted member 32524]

My understanding is same as yours operating with all other appliances on. 3 burners on for cooker and fire on too. I work out each sections kw requirement and size the pipe accordingly. Not very often you get an installation that does not require upgrading to conform to 1mb drop.

 

[cmarkr]

My understanding is same as yours operating with all other appliances on. 3 burners on for cooker and fire on too. I work out each sections kw requirement and size the pipe accordingly. Not very often you get an installation that does not require upgrading to conform to 1mb drop.

Thank you very much for your reply Duncan, i'm glad you agree i'm right in the way i'm currently working. These other two people who have told me i'm wrong have really put a doubt in my head that i'm doing this basic operation wrong....

 

[bacon_sandwich]

The only thing i would add is that i would get a reading at the meter at maximum demand, not just the fire running, then subtract 1mB from that reading for each appliance. Whether you run one appliance or all appliances is a subject of debate and what is in effect "maximum demand".
If you test with all appliances running flat out and it passes, no problem. If all three running flat out puts you just over then it gets into "probability of all appliances running at 100%" - hope this helps.
BTW, its very rare in a domestic for all appliances running at 100%.
I only do commercial and its more common to have all appliances running 100% at least for the first few hours in the morning, so i run them all to test for PD.

 

[cmarkr]

The only thing i would add is that i would get a reading at the meter at maximum demand, not just the fire running, then subtract 1mB from that reading for each appliance. Whether you run one appliance or all appliances is a subject of debate and what is in effect "maximum demand".
If you test with all appliances running flat out and it passes, no problem. If all three running flat out puts you just over then it gets into "probability of all appliances running at 100%" - hope this helps.
BTW, its very rare in a domestic for all appliances running at 100%.
I only do commercial and its more common to have all appliances running 100% at least for the first few hours in the morning, so i run them all to test for PD.

Thanks for your reply, Please can i just confirm you measure your meter outlet working pressure you normally take with all appliances on in the house? I have done this before as sometimes the meter working pressure changes everytime you add another appliance load to it;
E.G:
Meter outlet pressure 22mb with just fire on
Meter outlet pressure 21.2mb with fire and cooker on
Meter outlet pressure 20mb with all appliances running

Would it then be correct to use my lowest meter outlet pressure as my benchmark for pipesizing in these scenario's?

"If all three running flat out puts you just over then it gets into "probability of all appliances running at 100%" - hope this helps.
BTW, its very rare in a domestic for all appliances running at 100%."

I'm in complete agreeance with this comment but is this "probability of all appliances running at 100%" a documented thing or more of a GSI funnyhand shake it'll do kinda thing?

 

[bacon_sandwich]

Thanks for your reply, Please can i just confirm you measure your meter outlet working pressure you normally take with all appliances on in the house? I have done this before as sometimes the meter working pressure changes everytime you add another appliance load to it;
E.G:
Meter outlet pressure 22mb with just fire on
Meter outlet pressure 21.2mb with fire and cooker on
Meter outlet pressure 20mb with all appliances running

Would it then be correct to use my lowest meter outlet pressure as my benchmark for pipesizing in these scenario's?

"If all three running flat out puts you just over then it gets into "probability of all appliances running at 100%" - hope this helps.
BTW, its very rare in a domestic for all appliances running at 100%."

I'm in complete agreeance with this comment but is this "probability of all appliances running at 100%" a documented thing or more of a GSI funnyhand shake it'll do kinda thing?

The reason i do it this way is i am trying to find the worst case scenario. So if you are going to measure the pressure at the appliance when all appliances are running it makes sense to measure it at the meter under the same conditions, then you know how much you loose in the pipework.
I dont do domestic, so dont have the books to hand but i have "heard" of diversity being applied rightly or wrongly , hopefully some of the boys on here can comment on whether they run all or just the largest

 

[king of pipes]

I have always calculated the PD with the boiler at max rate Gas fire on full and three burner rings on a cooker a monometer on the appliance inlet and and a u gauge at the gas meter test point take readings at each appliance to check the pipe sizing on each section accross the gas installation pipework as other have stated it is highly unlikely that a the appliance will ever operate at these rates , Regards Kop

 

[ShaunCorbs]

Where are you testing from ? Also what’s meters inlet pressure

 

[cmarkr]

I have always calculated the PD with the boiler at max rate Gas fire on full and three burner rings on a cooker a monometer on the appliance inlet and and a u gauge at the gas meter test point take readings at each appliance to check the pipe sizing on each section accross the gas installation pipework as other have stated it is highly unlikely that a the appliance will ever operate at these rates , Regards Kop

Cool thanks for your input KOP, im glad your method is the same as mine too! Really appreciate your comment

Where are you testing from ? Also what’s meters inlet pressure

Hi Shaun, neither this scenario is fictional i'm more so checking my current working method is correct as i've been told its not/im being to strict on this whole 1mb pipesizing thing.

Generally if boiler i would check at a test point below the boiler (glow worm etc) if not the gas valve inlet. And before we open another can of worms im aware of internal drop on boilers.
Fires, inlet test point before fire
Cooker, either the small injector or test point behind cooker after bayonet.

Does my method in my 1st post seem the same way you operate, or would you mind telling me how you do this?

Thanks very much
Mark

 

[ShaunCorbs]

With all appliances running go round testing each one is no more than 1 mbar drop plus any restrictions eg gas valves etc

So meter inlet 22mbar
Boiler 19.5 mbar (1.5mbar restriction)
Cooker 21mbar
Fire 20.5mbar (0.5 mbar restriction)

Restriction will be listed in any mi you have

 

[cmarkr]

With all appliances running go round testing each one is no more than 1 mbar drop plus any restrictions eg gas valves etc

So meter inlet 22mbar
Boiler 19.5 mbar (1.5mbar restriction)
Cooker 21mbar
Fire 20.5mbar (0.5 mbar restriction)

Restriction will be listed in any mi you have

Thank you Shaun i really appreciate you taking the time to help me understand,

Hopefully my last question on the subject, looking at what you've written in your example, If you were to fit a new gas fire, would you be responsible to ensure just your appliance has the 1mbar drop allowance as in fix the 0.5mbar restriction on that leg. Or as your fitting a new appliance (the fire) are you responsible for at the same time up-rating the restricted leg to the boiler and any other restriction to other existing appliances?

Thanks again

 

[ShaunCorbs]

By restriction I mean testing from a gas valve etc normally says to allow let’s say Worcester 1.5mbar for testing pressure from the gas valve so you will expect a 2.5mbar drop

Hope this helps as I read yours as you need to fix the restriction