Adding 3 metres of 28mm pipe at the end of a 15 metre 22mm run

[bill577]

you can buy a 15m tracpipe rerun for about £240, might be easier to rerun the whole gas carcass than fart about putting bits in.

 

[GQuigley67]

so who re-routed the pipework ?

 

[boilerwoes]

so who re-routed the pipework ?

It was all part of the building work (so the builders who i kicked out) so they would have contracted someone I think. Don't have the details of the actual person who did it so can't get him back to sort it. The original pipes were put in by another company.

 

[boilerwoes]

you can buy a 15m tracpipe rerun for about £240, might be easier to rerun the whole gas carcass than fart about putting bits in.

Only problem is that it will either involve digging walls in addition to lifting floor boards (we would need to lift some floor boards in any case for upgrading sections to 28mm) so would rather not look at this option unless absolutely necessary

 

[fuzzy]

I don't know - just trying to summarise the points from the posts. Looks like the later posts say that increasing pipe size anywhere will increase volume, decrease resistance and increase working pressure at the appliance. The issue I am facing is that the pressure drop from gas meter to boiler is too great (around 6mbar) so am trying to determine ways of reducing this pressure drop. I am assuming the gas supply people won't change the governor to increase the gas meter pressure to above 22mbar?

increasing the pressure at the govener would not alter the drop in pressure across the system, they wouldnt do it anyway. you could do some pipe size calcs and work it out, normally its just a case of upsizing. Have you checked youve not got the manometer on the wrong size of the appliance have you and getting burner pressure? wouldnt be the first time somebody done that

 

[bill577]

increasing the pressure at the govener would not alter the drop in pressure across the system, they wouldnt do it anyway. you could do some pipe size calcs and work it out, normally its just a case of upsizing. Have you checked youve not got the manometer on the wrong size of the appliance have you and getting burner pressure? wouldnt be the first time somebody done that

The vaillant ecotec has a zero pressure govenor so no burner pressure to check.

 

[GQuigley67]

the OP isnt an engineer anyway

 

[fuzzy]

The vaillant ecotec has a zero pressure govenor so no burner pressure to check.

should be zero then

 

[boilerwoes]

The vaillant ecotec has a zero pressure govenor so no burner pressure to check.

Not sure I follow. What pressure would they have checked at the boiler then? He seemed to connect a manometer to something in the boiler. Would this be the pressure of the gas just before it hits the burner?Is anyone able to run a quick calculation to see what improvement I get in terms of pressure drop if I swap 5m of 22mm pipe with 5m of 28mm pipe?

 

[GQuigley67]

how much gas m3/hr does the boiler use ?

edit: I see its a 31kw boiler so 2.79 m3/hr I will go and get my sizing table and have a look

 

[GQuigley67]

not much at all your only losing 0.25mbar through that amount of pipework in 22mm you have to factor in bends and Tees aswell to get the total length

5m 22 = 0.25mbar
5m 28 = 0.16mbar

 

[fuzzy]

there could be a fault/block on the pipework?

 

[tamz]

Ignoring the hob.

The pressure drop you have is down to more than you are stating.
A 15m x 22mm run with 10 elbows to the tee
then
3m x 22mm + 1m x 15mm + 1 elbow from tee would give an overall drop of around 1.68mb (it would be around 2.34mb allowing for a 7kw hob)

The 15mm part somewhere under the floor has never been upgraded. Get it done again and done right this time.

 

[buckley plumb]

dont forget with a vailant you can lose 2mb wk press through the inlet elbow to the test point this is in the manual. i fitted a a large kw glowworm flexicom a while back and used a rear piping jig which only allowed 15mm pipe to the boiler from the top that reduced the wk press i cut a tee in and fitted test point on the 22mm part and got 20mb wk there .

ant

 

[GQuigley67]

dont forget with a vailant you can lose 2mb wk press through the inlet elbow to the test point this is in the manual. i fitted a a large kw glowworm flexicom a while back and used a rear piping jig which only allowed 15mm pipe to the boiler from the top that reduced the wk press i cut a tee in and fitted test point on the 22mm part and got 20mb wk there .

ant

true indeed I was told at one of their courses that they allow 2.5mbar to be lost at inlet

 

[tamz]

true indeed I was told at one of their courses that they allow 2.5mbar to be lost at inlet

That is a big get out of jail card for some :wink:

 

[mickie]

increasing the working pressure at the meters govner will increase the working pressure at the boiler, who ever said it wont is wrong because while the gas board was out i got him to up it a little while he was upgrading it, which did help a lot

 

[boilerwoes]

Ignoring the hob.

The pressure drop you have is down to more than you are stating.
A 15m x 22mm run with 10 elbows to the tee
then
3m x 22mm + 1m x 15mm + 1 elbow from tee would give an overall drop of around 1.68mb (it would be around 2.34mb allowing for a 7kw hob)

The 15mm part somewhere under the floor has never been upgraded. Get it done again and done right this time.

Thanks for the calculations. I do think it is a bit odd as before the building work, the working pressure at the boiler was 19mbar, so they must have screwed something up, but what? I am pretty sure 22mm pipe was added to the run for the hob (as the 22mm pipe was tee-d off the pipework going to the boiler). But I am wondering whether there is a blockage in the system. Maybe something is in the pipework that could be causing this significant pressure drop? Are there standard ways of flushing out debris, etc from gas pipework?

I guess the worse case scenario is to re-lay pipes etc, and I will need to have a think as to whether I want them in the walls or under the floors.

 

[GQuigley67]

it would yes but the pressure drop would still be the same

 

[boilerwoes]

increasing the working pressure at the meters govner will increase the working pressure at the boiler, who ever said it wont is wrong because while the gas board was out i got him to up it a little while he was upgrading it, which did help a lot

Is there a maximum working pressure at the meters governer that the gas board will allow? I am wondering whether to ask them to increase the pressure (if possible) and then resign myself to the fact that there is a large pressure drop, but at least the working pressure at the appliances are higher? Thoughts on this approach?

 

[boilerwoes]

it would yes but the pressure drop would still be the same

I am assuming you are referring to my question about the gas board increasing the pressure at the governor. In terms of the pressure drop being the same, I could live with that as long as the pressure to the appliances is high enough. So my next question is whether having a large pressure drop in the system is allowable as long as the appliances have their minimum required working pressure?

 

[mickie]

the working pressure is their to make sure a hob or another gas appliance doesnt go out while a boiler is running, also most boilers wont work properly with a working pressure of say, 15mb..

if you only have a boiler and nothing else, and the burner pressure is spot on, just the working pressure is down its only ncs, it wouldnt be dangerous.

 

[fuzzy]

I am assuming you are referring to my question about the gas board increasing the pressure at the governor. In terms of the pressure drop being the same, I could live with that as long as the pressure to the appliances is high enough. So my next question is whether having a large pressure drop in the system is allowable as long as the appliances have their minimum required working pressure?

doesnt matter if you can live with it or not, there should be no more than a 1mb drop across the system. there are reasons why the working pressures are controlled at the meter governor, if not you could run it in 10mm and just boost the pressure, but then its not safe

 

[bill577]

The minimum that vaillant allow is 17mb, I would disconnect the boiler and hob and blast some compressed air through the pipes, as the pipes have been cut to install a tee for the hob the installers may have got dirt ect in the pipe.

 

[boilerwoes]

doesnt matter if you can live with it or not, there should be no more than a 1mb drop across the system. there are reasons why the working pressures are controlled at the meter governor, if not you could run it in 10mm and just boost the pressure, but then its not safe

Thanks Fuzzy - that's why I asked the question as I wasn't sure if there are regulations that state it can't be more than 1mb or not. Sounds like you are saying that there are regulations that state there cannot be more than a 1mb drop, full stop. So even if they were to up the pressure at the governor (to say 25mb), to allow about 19mb at both appliances, there would still be a "breach" of the regulations as the drop is 6mb.

So it sounds like the only option I have is to fix the fact that there is a 6mb drop across the pipework (either find source of blockage or re-lay new pipe), and reduce that to no more than 1-2mb. Is that right?

 

[boilerwoes]

The minimum that vaillant allow is 17mb, I would disconnect the boiler and hob and blast some compressed air through the pipes, as the pipes have been cut to install a tee for the hob the installers may have got dirt ect in the pipe.

Sounds like a sensible first option - is compressed air etc a standard piece of kit to expect RGI's to have with them?

 

[boilerwoes]

the working pressure is their to make sure a hob or another gas appliance doesnt go out while a boiler is running, also most boilers wont work properly with a working pressure of say, 15mb..

if you only have a boiler and nothing else, and the burner pressure is spot on, just the working pressure is down its only ncs, it wouldnt be dangerous.

I have a boiler and a 4-burner hob. What's the difference between burner pressure and working pressure? I thought they were the same thing? There is also a concept of standing pressure, right?

 

[fuzzy]

Thanks Fuzzy - that's why I asked the question as I wasn't sure if there are regulations that state it can't be more than 1mb or not. Sounds like you are saying that there are regulations that state there cannot be more than a 1mb drop, full stop. So even if they were to up the pressure at the governor (to say 25mb), to allow about 19mb at both appliances, there would still be a "breach" of the regulations as the drop is 6mb.

So it sounds like the only option I have is to fix the fact that there is a 6mb drop across the pipework (either find source of blockage or re-lay new pipe), and reduce that to no more than 1-2mb. Is that right?

not a direct reg as far as im aware. its purpose is for design. there incoming pressure is 21mb (+-2mb) so you should get 20mb at appliance. Although some appliances as previously mentioned can operate fine on less incoming pressure that is just that appliance. they need guidelines for design, they have said 1mb max drop or classed as ncs

 

[mickie]

burner pressure = appliance
working pressure = pipework

both got with appliance running

 

[fuzzy]

I have a boiler and a 4-burner hob. What's the difference between burner pressure and working pressure? I thought they were the same thing? There is also a concept of standing pressure, right?

burner pressure can be lower than working pressure. one is before appliance regulator and one after. you need say 20mb working pressure at appliance and mis for burner pressure, could be 14mb, bu reduced at source. the appliance regulator is designed to work with incoming pressures of around 20mb. if somebody boosted meter regulator then this incoming pressure could/would be more and the applaince regulator is not designed for that (not saying it wouldnt work, not sure why it wouldnt, unless seriously high but not worth risk)

 

[fuzzy]

burner pressure = appliance
working pressure = pipework

both got with appliance running

working pressure at appliance and at meter

 

[mickie]

feeling a bit uncomfortable now, a little too much info

 

[boilerwoes]

feeling a bit uncomfortable now, a little too much info

Don't be - I am not daft to touch anything gas related. To be honest, not even practical enough to sort out plumbing issues (I get a plumber to sort out leaks on rads etc), but I like to understand and know about issues (boiler, gas, water, etc) and potential resolutions. Having been messed around by dodgy tradesmen (RGI or otherwise), I want to make sure I know what's what first.

For example, I now know to push for them first trying compressed air to clear any blockage. I also know that the builders screwed something up as technically, there shouldn't be a significant pressure drop (based on the calculations posted earlier).

 

[tamz]

is compressed air etc a standard piece of kit to expect RGI's to have with them?

Definately not.

 

[bill577]

If you let the rgi know that you want the pipes cleared with c/air he should be able to get a hold of a compressor (I use my scuba cylinders if I want to clear pipes).