Gas question...

[David Herman]

Hi,

We have a number of gas appliances and just wondering what you think...

1 * 35,000 BTU 1* 50,000 BTU 2 * 125,000 BTU 1 * 250,000 BTU

Now... out main question is around the larger sized btu boiler (the swimming pool heater). As it stands, its outside so when the house was made the pipe was obviously layed. The pipe is 1" or 1 + 1/4" (I think). But where it comes out of the ground, its conected with a 1/2" to the boiler (about 1 and a bit meters). If we were to have that small stretch of pipe increased in size, would we see an increase of flow? As it stands the boiler is working, but not running with enough gas as it really should be...

Cheers,

David Herman

[IMM]

Take it up to 22mm. The 250,000 BTU.hr boiler take 250 cu ft/hr. I know of no boiler that requires a 1/2" connection of that rating.

[tarquinlinbin]

I wonder what size meter and service pipe you have...?

[David Herman]

Its a commercial size meter...

On another note...

Out of the meter it is 1" pipe. Then it all get's T'd off for each of the appliances. I suspect its worth pulling a few tiles up and replacing that stretch of pipe too with a larger one?

Dave

[IMM]

The meter should be a U16. 16 cu metres/hr, about 560 cu foot/hr. What does it say on the meter dial? A U16 has 1 1/4" connections. Best to have a 1

1/4" to 1 1/4" BSP meter union on the meter outlet. Have 1 1/4" iron fittings and short pieces and then tee off to the appliances that way.

has all the fittings.

[John]

On what do you base your theory about it not getting enough gas - is it a guess or has someone actually carried out measurements?

[John]

It is not possible to give you a definitive comment on your gas system without full details and dimensions of pipes, lengths of run, loads on each bit etc. but keep in mind that when all appliances are running at their full rated load the pressure drop between the meter and the appliance inlet should not exceed 1millbar. Any length of pipe can be crudely considered as a resistance and the drop along that length depends on the rate of gas flow and the size of the section of pipe. If you have a short length of small pipe it will drop a certain amount of pressure under dynamic flow conditions but this when added to the drop along the next section and the next section after that may still not exceed the allowed drop between meter and appliance. Thus its not possible to simply apply a rule of thumb without at least making an analysis of the system. A foot or so of 1" pipe even with a very heavy load will likely not cause a measurable drop. However if you can make a sketch of the pipesystem (line diagram) with the various lengths as mentioned above and post it to a website say so readers can look at it we might be able to give you a proper answer. Also show elbows and tees because each of these gives an equivant pressure drop.

[David Herman]

I'll do that this evening :-)

I'll try and give all details...

David Herman

[David Herman]

A measurement has been carried out... It was quite a bit lower than it should have been.

Dave

[IMM]

You have to be joking! Look at the consumption. Oh you have..

However if you can make a sketch of the pipesystem (line

[Ed Sirett]

The pressure drop on the 1.5m (say) length of 1/2" alone is about 1 mbar per meter.

[David Herman]

OK...

So this is all to the best of my knowledge.

Meter: Qmax 16m^3/n Qmin 0.32^3/n Pmax 75mbar V 4dm^3

From the meter -> Flexible silver pipe to a valve (quarter turn) Valve -> 1" pipe (1 meter) Pipe -> 5 pipes T'd off

1 * 1/4 inch - Aga 1 * 1/4 inch - Gas Fire 2* 1/2 inch - Boilers 1 * underground pipe to swimming pool (15meters) -> to the 3/4inch pipe which supplies the swimming pool boiler

I can't see how it's been T'd off because its been done under some tiles. I suspect it was done in a crap way, as we have had lots of problems with the builders/fitters back when the house was constructed.

Dave

[John]

Are you meaning the inlet (supply from the street) here or is the outlet from meter to your system also in flexible?

1/4 inch sounds exceedingly small are you sure about that? also needed is the length approximately and the number of bends in it. What does the data plate on the aga give for its heat input?

ditto

ditto

are ther any bends in this and to save cross referring back and forth can you give the gas rate (input heat) of this also

A tee is a tee is a tee as long as its sound it should be allright

BTW has there been a development which has caused you to look into this or has it always been like it?

Also worth quoting to us is the actual burner pressure needed by the appliances as given on the data plates or from the installation and service booklets. Its also just possible that even with an excessive pressure drop to an appliance by the standards, the appliances burner governor may still be able to cope with this so even though not complying with regs it still "works" safely