Trainee gas questions in this thread ONLY please

[bassmonster]

hey all,
I'm just ticking off the boxes in my completed tasks folder for my ACS and for some reason my mind has gone completely blank.

Ok, so in all my 12 jobs, i have to carry measure operating pressure on the appliance. correct me if i'm wrong, you cannot carry out operating pressure if the boiler has a zero governor ? is there any other way of measuring the operating pressure on a boiler with a zero governor like through some calculation with the meter?

 

[TBServices]

Gas rate and check combustion is only option really

 

[GrahamM]

Operating pressure/burner pressure cannot be taken on zero governed boiler. This is when a gas rate is required.

 

[heliotrope]

I suspect the OP means the working pressure of the appliance rather than the
burner pressure.

The working pressure is the pressure delivered at the appliance, this would usually
be taken from a test point very near to the appliance or from the gas valve P1 point
on the valve.

 

[TBServices]

Irrelevant on a zero governor as there is a vacuum in the pipework and you will never get a correct measurement.

If it's gas rated correctly and the combustion is okay, the it's fine.

 

[GrahamM]

Irrelevant on a zero governor as there is a vacuum in the pipework and you will never get a correct measurement.

If it's gas rated correctly and the combustion is okay, the it's fine.

Disagree.
You can still check working pressure on a zero governor and I still do at times. You should still get around say 16mb minimum on a greenstar at P1 for example.

 

[Killy Bing]

Disagree.
You can still check working pressure on a zero governor and I still do at times. You should still get around say 16mb minimum on a greenstar at P1 for example.

Hes talking about burner pressure.

you should always check working pressure at p1!

 

[TBServices]

Disagree.
You can still check working pressure on a zero governor and I still do at times. You should still get around say 16mb minimum on a greenstar at P1 for example.

You can check at the test point but the reading is almost meaningless with the appliance running.

 

[stevetheplumber]

so how do you know you have less than a 1 mb drop on your pipework?working inlet pressure should be measured and a zero govenor will have no effect

 

[TBServices]

You can't. Because gas isn't just travelling down the pipe under positive pressure, it's being sucked through the pipe under negative pressure. Why do you think the manufacturers quote such low book figures for inlet reading?

Ideal quote as low as 14mb at the test nipple.

 

[AWheating]

You can't. Because gas isn't just travelling down the pipe under positive pressure, it's being sucked through the pipe under negative pressure. Why do you think the manufacturers quote such low book figures for inlet reading?

Ideal quote as low as 14mb at the test nipple.

you cant be sure you have 1mb drop without a fitted test point really. but you can check that the pipework has no more than a 2.5mb drop from the meter which would def indicate with most appliances the gas pipework is undersized and a risk to other appliances.

the min working pressures stated by the manufacturer is only supposed to be seen when gas supply pressures are low and not badly sized pipework. Ideal are stating that the boiler works safely at that pressure, with a consideration of16mb meter working pressure at "peak" times being thought about.

 

[bassmonster]

Thank you for the replies.

My portfolio states that it's "operating pressure" which i need to record. does that mean the term "working pressure" is the same thing?

when connecting the gauge to the p1 test point, would i record the pressure whilst the appliance is running or off?

am i correct in thinking that even a zero governor gas valve will have a p1 test point?

 

[AWheating]

The p1 point mentioned is the gas inlet test point. It will give you the working inlet pressure at the gas valve. The operating or burner pressure will be zero more or less. In the box for operating pressure either put the gas rate or write zero, zero guvna.

Yes the gas valve will prob have both inlet and burner test points.

 

[bassmonster]

The p1 point mentioned is the gas inlet test point. It will give you the working inlet pressure at the gas valve. The operating or burner pressure will be zero more or less. In the box for operating pressure either put the gas rate or write zero, zero guvna.

Yes the gas valve will prob have both inlet and burner test points.

why did i not think of that..?:thinking::thinking::thinking:

thanks mate.....

 

[acecharly]

In your practical assessments you will most likely be asked to check the working pressure on a zero governor burner, to check that when you get the zero reading you understand what type of control you are dealing with.

 

[bassmonster]

what physical components differentiates between a zero governor and another type?

 

[acecharly]

You have a zero governor and a constant pressure governor.

In a constant pressure governor the spring inside acts downwards on the diaphragm.

In a zero governor the spring holds the diaphragm against its seating.

 

[bassmonster]

can you tell which is which just by looking at the gas valve?

 

[acecharly]

If your familiar with the boiler in question yes. If not a quick test with your gauge will tell you.

 

[Killy Bing]

if its a premix burner it will have a zero governor

 

[AWheating]

[DLMURL]http://www.radmidlands.co.uk/Downloads/ControlsDom.pdf[/DLMURL]

page 6

https://docs.google.com/file/d/0B6zTTicYyEudZnhHUVlSRnI5cVk/edit

another good source of info for guys learning the trade.

 

[combo]

Vaillant ecomax says you must have 17-25 mb at P1...this is to check the meter/pipework can supply the correct volume of gas at full working pressure. The vacuum created by the fan to premix the burner does not affect the P1 value, it only affects the P2 value ie a negative pressure........Am I right in saying this ?

 

[combo]

I guess what im saying is, these low mb inlet pressures are to allow for the usual possible pressure losses such as; 2mb WP, 1mb pipeloss, and the possible loss across meter at peak network...its nothing to do with the air/gas valve.

 

[AWheating]

yes your correct that the p1 (inlet) reading should not be effected by the way the gas valve uses the gas. No matter what the situation you are not allowed more than a 1mb drop from the meter test point to the point of connection at the appliance. The manufacturer may state its internal pipework and filters will show a 1-2.5mb drop from this conection to the inlet test point at the gas valve. But this manufacturers drop can not be used to avoid correctly sizing of the gas supply.

so i think for a WB you could have 19mb working pressure, 1mb drop on pipework, 1.5mb drop inside the appliance giving you a min working pressure of 16.5mb as required in the instructions.

 

[Barry98]

For trainees to ask questions prior to passing gas safe

 

[Dotty]

Thread from open forum merged in. Sorry Lee, it's bumped your post down!

 

[bassmonster]

Unsafe situation? It only has a rubber seal on the outside but not cemented inside.....

 

[kirkgas]

Depends on MI of specific boiler, some allow rubber collar to be used as weather seal, only required on the outside to stop POC's re entering property and going up cavity, inside seal is only for decor

 

[bassmonster]

Thank you Kirk. I'll have a nosey in the MI to be sure

 

[albatross]

Unsafe situation? It only has a rubber seal on the outside but not cemented inside.....

View attachment 17879

View attachment 17880

If neither wall is cemented its at risk. Flue must be sealed to the building with cement.(not expanding foam/silicone. Also flue must be adequately supported and the rubber will not do that and just being attached at the boiler is not good enough. If it was low enough some flues could work loose/ be pulled out causing fumes to go into the room if not securely cemented in.

 

[Killy Bing]

If neither wall is cemented its at risk. Flue must be sealed to the building with cement.(not expanding foam/silicone. Also flue must be adequately supported and the rubber will not do that and just being attached at the boiler is not good enough. If it was low enough some flues could work loose/ be pulled out causing fumes to go into the room if not securely cemented in.

reminds me, i have a flue i need to go fit....
damnit

 

[tamz]

If neither wall is cemented its at risk. Flue must be sealed to the building with cement.(not expanding foam/silicone. Also flue must be adequately supported and the rubber will not do that and just being attached at the boiler is not good enough. If it was low enough some flues could work loose/ be pulled out causing fumes to go into the room if not securely cemented in.

Depends on the manu. Worcester and vaillant don't care much but baxi and vokera want it sealed.
Common sens says mix up some compo but common sense also says i've more chance of having a heart attack humping Kylie than anyone ever being at risk of anything.

 

[kirkgas]

Albatross, EVERY un cemented flue isn't AR, you need to be boiler specific when you say that as some manufacturers allow the rubber seal, in fact (can't remember make model) I remember we fitted some boilers in 5 high flats and chose the boiler as we could fit the flue and rubber seal from the inside, I'm sure we had to drill 6" hole rather than 5" to accommodate rubber ring going through from inside, I've always done what manufacturer said, but on contracts where we had builders on site anyway I always got them to cement the flue holes, but I wasn't paying for a 5 high scaffold to seal them when I could choose a different boiler and fit flue from inside, the wall on the inside is only for decor, if the flue corrodes the POC's would go up the cavity, and any fumes blowing back in from outside would always go up the cavity rather than right back into the house

 

[albatross]

Albatross, EVERY un cemented flue isn't AR, you need to be boiler specific when you say that as some manufacturers allow the rubber seal, in fact (can't remember make model) I remember we fitted some boilers in 5 high flats and chose the boiler as we could fit the flue and rubber seal from the inside, I'm sure we had to drill 6" hole rather than 5" to accommodate rubber ring going through from inside, I've always done what manufacturer said, but on contracts where we had builders on site anyway I always got them to cement the flue holes, but I wasn't paying for a 5 high scaffold to seal them when I could choose a different boiler and fit flue from inside, the wall on the inside is only for decor, if the flue corrodes the POC's would go up the cavity, and any fumes blowing back in from outside would always go up the cavity rather than right back into the house

It is. Gas Regs say a flue must be supported and there must not be an opening in the building within 300mm.

You can do what you just said as long as you cement the inside course and just have the rubber outside. Then you have supported the flue and sealed it. I have done it too.

 

[Mike Jackson]

Gas Regs don't. Building regs do but MIs supersede building regs.