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Low gas pressure

View the thread, titled "Low gas pressure" which is posted in Gas Engineers Forum on UK Plumbers Forums.

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newcastle phill said:
Nope your looking at the tables wrong. That 2.9m3 refers to a 3m length of 15mm with a 1mb drop.
A mere 20 cm section would flow alot more than that...by my loose reckoning easily in excess of 5m3
Click to expand...

I wasn't looking at a table. I was using the mr combi pipe size app and for the length of 15 I have with 1 elbow you won't get higher, needs to be 22

ceeca4987ac4bf7f57e40853133693df.jpg


9410c5b79e6e2a1fdacbd3cefb2fa479.jpg
 
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Why not put a reducer on the connection from the boiler and take it straight to 22 or 28? That's what I do with boilers which have 15mm connections. I would also tee the hob off either the 22 or 28mm pipe.
 
App. and Tables in agreement 2.9 flow gives 3 meters and 20 meters for 15 &22.
Length 700mm pressure drop 700/3000 & 700/20000 which equates to the 0.233 & 0.035 given by App.
Phil also right with flow through 700mm length of 15mm. 1/4 of 3 meter length could be expected to give double the 3 meter flow, ( L X Q X Q approx constant).
 
joni os said:
App. and Tables in agreement 2.9 flow gives 3 meters and 20 meters for 15 &22.
Length 700mm pressure drop 700/3000 & 700/20000 which equates to the 0.233 & 0.035 given by App.
Phil also right with flow through 700mm length of 15mm. 1/4 of 3 meter length could be expected to give double the 3 meter flow, ( L X Q X Q approx constant).
Click to expand...

Why does the app say for 2.91 with an effective length of 700mm you need 22?
 
mfgs said:
Why not put a reducer on the connection from the boiler and take it straight to 22 or 28? That's what I do with boilers which have 15mm connections. I would also tee the hob off either the 22 or 28mm pipe.
Click to expand...

I will do from now on! But from what Phil and Joni say I should get enough flow from that short run of 15 ... so what gives?
 
Can you upload a drawing. Something doesnt add up here from what youv'e said.
 
Sorry if you have answered this before, but what is the working pressure at the meter?
 
I dont use apps or rather put an over reliance on them. Pen and paper is best. But ive downloaded one that says different anyway which is more in line with my ready reckoning.

And 30kw is 30kw wether its vaillant, ideal or heatline - its not the boiler. As this demonstrates that small bit of run can handle upto a theoretical 45 ish kilowat

Edit.
Yep accurate drawing of the run.


88eb41eeaf34feb9215e52b32e81ca7a.jpg
 
Last edited by a moderator:
newcastle phill said:
I dont use apps or rather put an over reliance on them. Pen and paper is best. But ive downloaded one that says different anyway which is more in line with my ready reckoning.

And 30kw is 30kw wether its vaillant, ideal or heatline - its not the boiler. As this demonstrates that small bit of run can handle upto a theoretical 45 ish kilowat

Edit.
Yep accurate drawing of the run.


88eb41eeaf34feb9215e52b32e81ca7a.jpg
Click to expand...

What app is that Phil?

Agreed re: heat input ratings.. I've tried drawing it and my drawings are confusing.. but basically there are 24 elbows, 2 45s and approx 14 meters of 28mm.
 
Very experienced Gas Engineer was perplexed to be reading 16 at meter with his brand new certified digital manometer. Explanation, it was set for mmHg instead of mbar. Trust nothing at first sight.
 
joni os said:
Very experienced Gas Engineer was perplexed to be reading 16 at meter with his brand new certified digital manometer. Explanation, it was set for mmHg instead of mbar. Trust nothing at first sight.
Click to expand...

Lol oh dear!! I used a manual wet u-gauge though
 
I cant put that into a visual way.

But all id say is if youve teed off the 15mm to the hob - I wouldn't have done that. Id have teed off the 28 to the hob and left that final 15mm run to the boiler unimpinged.
 
newcastle phill said:
I cant put that into a visual way.

But all id say is if youve teed off the 15mm to the hob - I wouldn't have done that. Id have teed off the 28 to the hob and left that final 15mm run to the boiler unimpinged.
Click to expand...

I hear you about the hob. If need be I'll change it. But even with the hob disconnected from the supply it didn't change the readings I got for the boiler.
 
Was the 21.5 at the meter with the boiler on max or just with the hob on.
And as everyone elce is saying dont have the hob and boiler both of the same section of 15mm pipe.
 
Was the 21.5 at the meter with the boiler on max or just with the hob on?
And as everyone elce is saying dont have the hob and boiler both of the same section of 15mm pipe.
 
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