Hope this doesn't turn into one of those "I do this - I do that" posts
ps I'm a bodmas man myself
tell me what bodmas is i want to know if im a bodmas man
Gas pressure drop along pipework
- Thread starter iep
- Start date
tell me what bodmas is i want to know if im a bodmas man
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Big Old Dave Made A Sausage.
or Brackets, Of, Division, Multiplication, Addition and Subtraction.
The order in which you work out those sums D Hailsham posted.
or Brackets, Of, Division, Multiplication, Addition and Subtraction.
The order in which you work out those sums D Hailsham posted.
I could not even recall what Bodmas was until Sooey gave me the clue.
Now I vaguely remember BODMAS. But the good news is that I never found that problem very difficult as it all seemed logical to me.
The OP has probably not calculated the heat loss very accurately.
Since he does not mention his location I would love to know where it is that has temperatures -9°C below what we calculate our CH on.
As a bit of amusement its 24.3° outside here now and a very precise 21.0° indoors at which I feel totally comfortable.
Tony
Now I vaguely remember BODMAS. But the good news is that I never found that problem very difficult as it all seemed logical to me.
The OP has probably not calculated the heat loss very accurately.
Since he does not mention his location I would love to know where it is that has temperatures -9°C below what we calculate our CH on.
As a bit of amusement its 24.3° outside here now and a very precise 21.0° indoors at which I feel totally comfortable.
Tony
Have a glass of sherry then Tony
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Wow, go away for a couple of days and all sorts of weird stuff gets written.
Anyway, a bit of actual data now. I got an RGI (mate of a mate) to do a quick flying visit yesterday afternoon.
Gas pressure measured at boiler inlet:
Boiler running in low flame mode: 12mb
Boiler running in High Flame mode: 8mb
Boiler off, gas oven and all hobs running at full: 20.5mb
Cooker and boiler share a common 22mm connection to the gas meter that Ts off at the cooker and then travels a further 10m (in 22mm) to the boiler.
The total power of the oven and all four hobs running at full is approx 15kW.
So, a massive pressure drop when the boiler is running that certainly explains why I'm not seeing full power. Must be one hell of a restriction to be causing nearly 10mb of pressure drop when the boiler is only running at approx 10kW.
The results also suggest that the blockage occurs after the gas main Ts off at the cooker (since running the cooker at full blast does not cause much of a pressure drop). I've traced it through though and (externally) it looks fine with no kinks or bad joints.
The RGI reckons a new gas main from the cooker to the boiler might fix the issue but was unable to see where the restriction could be occurring.
Also, as regards the location, we live in the Pentland hills south of Edinburgh. Last snow was three weeks ago and temp at night was still -3 degrees two weeks back! Amazingly though, it hit 29 degrees in the shade on Saturday so looks like summer is finally here.
I agree that my heat loss calculations won't be super accurate but with solid walls, single glazing and no loft insulation in half the house, I reckon they won't be far out.
D_Hailsham, thanks for the boiler suggestion. I'd not heard of these before. Just looked at the 24v and 18v models. Seem a bit too good to be true with a 5 year warranty and being about £100 cheaper than the WB 24ri. Any known issues with these?
Cheers,
iep
Anyway, a bit of actual data now. I got an RGI (mate of a mate) to do a quick flying visit yesterday afternoon.
Gas pressure measured at boiler inlet:
Boiler running in low flame mode: 12mb
Boiler running in High Flame mode: 8mb
Boiler off, gas oven and all hobs running at full: 20.5mb
Cooker and boiler share a common 22mm connection to the gas meter that Ts off at the cooker and then travels a further 10m (in 22mm) to the boiler.
The total power of the oven and all four hobs running at full is approx 15kW.
So, a massive pressure drop when the boiler is running that certainly explains why I'm not seeing full power. Must be one hell of a restriction to be causing nearly 10mb of pressure drop when the boiler is only running at approx 10kW.
The results also suggest that the blockage occurs after the gas main Ts off at the cooker (since running the cooker at full blast does not cause much of a pressure drop). I've traced it through though and (externally) it looks fine with no kinks or bad joints.
The RGI reckons a new gas main from the cooker to the boiler might fix the issue but was unable to see where the restriction could be occurring.
Also, as regards the location, we live in the Pentland hills south of Edinburgh. Last snow was three weeks ago and temp at night was still -3 degrees two weeks back! Amazingly though, it hit 29 degrees in the shade on Saturday so looks like summer is finally here.
I agree that my heat loss calculations won't be super accurate but with solid walls, single glazing and no loft insulation in half the house, I reckon they won't be far out.
D_Hailsham, thanks for the boiler suggestion. I'd not heard of these before. Just looked at the 24v and 18v models. Seem a bit too good to be true with a 5 year warranty and being about £100 cheaper than the WB 24ri. Any known issues with these?
Cheers,
iep
Based solely on what you have said there is probably a very simple cause of the low working pressure at the boiler.
Any experienced competent gas engineer would have immediately come up with the most likely cause and could have checked ( and sorted ) it in about 10 minutes if that was the cause.
But I cannot give gas work information on an open forum. But if your RGI were to phone me then I would tell him what it probably is.
Tony
Any experienced competent gas engineer would have immediately come up with the most likely cause and could have checked ( and sorted ) it in about 10 minutes if that was the cause.
But I cannot give gas work information on an open forum. But if your RGI were to phone me then I would tell him what it probably is.
Tony
This is a really common scenario that I would have thought any RGI with a years' exp would have come across.
There are several things which can block a gas pipe - eg water, rust, ptfe, flux, or sulphide. You do need an RGI to go in looking though.
On top of that, the tables we're given for working out gas pipe pressure losses are miles out in practice, especially on smaller pipes. Probably a surface effect, I don't know, but on 22mm pipe I'd allow an extra 50% drop at least. Old iron pipe is awful.
There are several things which can block a gas pipe - eg water, rust, ptfe, flux, or sulphide. You do need an RGI to go in looking though.
On top of that, the tables we're given for working out gas pipe pressure losses are miles out in practice, especially on smaller pipes. Probably a surface effect, I don't know, but on 22mm pipe I'd allow an extra 50% drop at least. Old iron pipe is awful.
Thanks guys. The guy in question is a local RGI who has an excellent reputation (did two of my friends heating installs).
Sunday was just a flying visit on his way home from doing some work at my mate's house but he is coming back to give the system a full inspection next week. Hopefully he'll be able to get to the bottom of it then.
In the meantime, I'll just hope the warm weather continues.
Obviously, I'll post the final diagnosis once I have it.
Cheers,
iep
Sunday was just a flying visit on his way home from doing some work at my mate's house but he is coming back to give the system a full inspection next week. Hopefully he'll be able to get to the bottom of it then.
In the meantime, I'll just hope the warm weather continues.
Obviously, I'll post the final diagnosis once I have it.
Cheers,
iep
The RGI has just been round and given the system a good going over. Diagnosis is that there is some form of restriction in the gas main between the T piece that feeds the cooker (where the pipe enters the kitchen) and the boiler which is at the end of a further 10m of pipe (8m in 22mm 2m in 15mm).
Pressure drops were as before (12mb drop between cooker and boiler when the boiler is running at 10kW). Pressure at cooker when boiler running is a healthy 21mb.
ChrisR and Agile, I'm not sure what your suspicions were but he checked the filter of the gas inlet valve and checked for any signs of scaling building up in the pipes. Both were very clean.
The next step is to start cutting out and replacing sections of the gas main which is going to make a right mess of our kitchen and ceiling. If anyone has any other ideas that I can look into before my RGI starts chopping up the gas main I'd be really grateful to hear them.
Cheers,
iep
Pressure drops were as before (12mb drop between cooker and boiler when the boiler is running at 10kW). Pressure at cooker when boiler running is a healthy 21mb.
ChrisR and Agile, I'm not sure what your suspicions were but he checked the filter of the gas inlet valve and checked for any signs of scaling building up in the pipes. Both were very clean.
The next step is to start cutting out and replacing sections of the gas main which is going to make a right mess of our kitchen and ceiling. If anyone has any other ideas that I can look into before my RGI starts chopping up the gas main I'd be really grateful to hear them.
Cheers,
iep
Took a while to find a plumber worth talking to (one guy turned up and took £40 to quote on the job and then fecked off never to be heard from again).
But, finally got it sorted yesterday. Removed the 2m section of 15mm pipe which connects from the back of the boiler up to the 22mm pipe in the loft. Inside the 15mm pipe was a small piece of 100 year old horsehair plaster!
All that we could guess was that 32 years ago, when they installed the gas main, they pushed the 15mm pipe up through the hole in the ceiling without putting some tape over the end. Crumb of old plaster fell in and, hey presto, 32 year of poor heating for the former owner. Fecking cowboys.
All fixed now though and my old glowworm energy saver 60 has a whole new lease of life.
Combined with complete new 22mm main feed/15mm spur pipework system that I installed last week (and the 9 new rads), I think/hope we'll e a lot more comfortable this winter.
Thanks again to those who contributed.
iep
But, finally got it sorted yesterday. Removed the 2m section of 15mm pipe which connects from the back of the boiler up to the 22mm pipe in the loft. Inside the 15mm pipe was a small piece of 100 year old horsehair plaster!
All that we could guess was that 32 years ago, when they installed the gas main, they pushed the 15mm pipe up through the hole in the ceiling without putting some tape over the end. Crumb of old plaster fell in and, hey presto, 32 year of poor heating for the former owner. Fecking cowboys.
All fixed now though and my old glowworm energy saver 60 has a whole new lease of life.
Combined with complete new 22mm main feed/15mm spur pipework system that I installed last week (and the 9 new rads), I think/hope we'll e a lot more comfortable this winter.
Thanks again to those who contributed.
iep
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