Question on gas pressure drop across pipework

[jaydebruyne]

I know it's 1mb drop max from meter to appliance.

a) is this with just that one appliance demanding gas?

 

[Chalked]

No mate.
Pipework should be sized so that all appliances will only have a max of one mb. When sizing, kW of all are added.
Don't you remember the pipework calc in the gas safe course?

 

[jaydebruyne]

No mate.
Pipework should be sized so that all appliances will only have a max of one mb. When sizing, kW of all are added.
Don't you remember the pipework calc in the gas safe course?

Ah yes.. sorry.. my brain is fried today! Forgot you divide the drop by number of appliances!!

 

[Last Plumber]

Do you know 'why' the drop we aim at is 1 mbar Jaydebruyne?

If you know that, you'll always remember why you're going to the trouble.

It will also help with your 'Engineers discretion '

 

[Last Plumber]

Do you know 'why' the drop we aim at is 1 mbar Jaydebruyne?

If you know that, you'll always remember why you're going to the trouble.

It will also help with your 'Engineers discretion '

 

[jaydebruyne]

Do you know 'why' the drop we aim at is 1 mbar Jaydebruyne?

If you know that, you'll always remember why you're going to the trouble.

It will also help with your 'Engineers discretion '

I feel like I should but no, I don't :/ why do we aim for a 1mb drop? I thought it was due to safety of appliances and how to tell if pipework was undersized

 

[Last Plumber]

I feel like I should but no, I don't :/ why do we aim for a 1mb drop? I thought it was due to safety of appliances and how to tell if pipework was undersized

It's because in the UK we have a lot of unregulated (pressure) appliances.
e.g. gas fires, wall heaters, hobs etc etc.

These appliances are designed to work on 20mbar (inlet working pressure).

For years, since the changeover to natural gas, we more often than not, had 21mbar at the meter outlet.

Therefore, in order to get the 20mbar at the appliance, we needed to make sure the calcs for pipe size were correct. ( 1 mbar drop).

You don't want too high or to low a pressure on any unregulated appliance.

It is also very important that the unregulated appliances are not effected by appliances sharing the same installation pipe work. ( like your hob on another post, recently).

Hope this helps !

 

[jaydebruyne]

It's because in the UK we have a lot of unregulated (pressure) appliances.
e.g. gas fires, wall heaters, hobs etc etc.

These appliances are designed to work on 20mbar (inlet working pressure).

For years, since the changeover to natural gas, we more often than not, had 21mbar at the meter outlet.

Therefore, in order to get the 20mbar at the appliance, we needed to make sure the calcs for pipe size were correct. ( 1 mbar drop).

You don't want too high or to low a pressure on any unregulated appliance.

It is also very important that the unregulated appliances are not effected by appliances sharing the same installation pipe work. ( like your hob on another post, recently).

Hope this helps !

Makes complete sense and this wasn't covered in my gas course!! Cheers Last

So with all appliances on, it shouldn't matter what appliance you test the drop at should it? i.e boiler and hob on and I test drop at boiler. As long as it isn't below (preferably for the unregulated appliances) or above 1 then you're good to go?

 

[ShaunCorbs]

test all appliances if a test nipple is present, just encase something is undersized further down,

and meter inlet working - permissible working drop = inlet of appliance (about)

normally you can tell by eye once you have a bit of experience (flame picture)

 

[jaydebruyne]

test all appliances if a test nipple is present, just encase something is undersized further down,

and meter inlet working - permissible working drop = inlet of appliance (about)

normally you can tell by eye once you have a bit of experience (flame picture)

Yeah I knew their hob wasn't right as flame pic had changed - top of flames on highest burners went yellow..

Sorry.. just need to ask.. so say I cut in a test point under the hob and under the boiler, I should get 1mb drop between them both - so 0.5 each (for arguments sake, I know this 0.5 will be different values depending on length of run, size of pipe etc to each appliance)

 

[ShaunCorbs]

Yeah I knew their hob wasn't right as flame pic had changed - top of flames on highest burners went yellow..

Sorry.. just need to ask.. so say I cut in a test point under the hob and under the boiler, I should get 1mb drop between them both - so 0.5 each (for arguments sake, I know this 0.5 will be different values depending on length of run, size of pipe etc to each appliance)

Yea all appliances drop = Pipework drop (under 1mbar)

 

[Last Plumber]

Yeah I knew their hob wasn't right as flame pic had changed - top of flames on highest burners went yellow..

Sorry.. just need to ask.. so say I cut in a test point under the hob and under the boiler, I should get 1mb drop between them both - so 0.5 each (for arguments sake, I know this 0.5 will be different values depending on length of run, size of pipe etc to each appliance)

You should ( in domestic, in theory and in a perfect world ), have 1 mb drop between the working pressure at meter outlet and same gas rate working pressure at each appliance inlet.

Test them with and without other appliances running.