Permissible drop and TT

[lame plumber]

You are not allowed any drop on pipework all appliances have service valves or should have.

the first bit has been pointed out, re service valves freestanding gas cookers?

 

[Keefy]

I've always understood it that if it's within the maximum acceptable drop with existing pipework and fittings you can leave it because the leak is so minute it would never reach it's explosive gas to air ratio due to other factors like ordinary room air changes. That's not to say I'd be comfortable leaving say, a 3 or 3 and a half mbar drop though, even though the law would allow me to.

 

[leethegasman]

the first bit has been pointed out, re service valves freestanding gas cookers?

Disconnect it from bayonet

 

[kel4783]

the question is would u leave a E6 meter with 8mb drop ???

 

[leethegasman]

I've always understood it that if it's within the maximum acceptable drop with existing pipework and fittings you can leave it because the leak is so minute it would never reach it's explosive gas to air ratio due to other factors like ordinary room air changes. That's not to say I'd be comfortable leaving say, a 3 or 3 and a half mbar drop though, even though the law would allow me to.

I have met a few installers that think this but you are not allowed any drop on any pipework new or old.

 

[neily01]

Done my resit in jan asked the trainer that exact question as it seems different people have different views. I was always taught any drop you must confirm carcase is sound by isolating app and he said this was correct. I have had a 2 mb drop on a llords which had been passed for years and after some investigating I found a unsoldered but fluxed 15mm elbow behind kitchen carcase.amazing how well flux will hold and over a long period!

 

[leethegasman]

the question is would u leave a E6 meter with 8mb drop ???

The 4mbar on a u6 and the 8mbar on a e6 is to do with the volume of gas within the meter.

 

[lame plumber]

Disconnect it from bayonet

but its not a service valve?

 

[lame plumber]

I have met a few installers that think this but you are not allowed any drop on any pipework new or old.

both of you are right but people need to read the complete posts and not extract bits of them or this will go on forever.

 

[johnnyplumb]

the book says you can leave a situation like this, but maybe the books wrong :disappointed:

a 2mb drop at 20mb would also show a drop on a 10mb let buy test.
if there's no drop at 10mb, you could be looking at a let buy on the ecv, with a gas leak equal to the let buy

so imo, only leave this situation if there's a drop on the 10mb let buy test as well :smile:

 

[leethegasman]

but its not a service valve?

But does give you a means of isolating the appliance from the pipework to carry out you tests.

 

[lame plumber]

But does give you a means of isolating the appliance from the pipework to carry out you tests.

you didnt say that earlier ( going for a proper bite here)🙂

 

[AWheating]

permissable drop


the name tells you what you need to know.

 

[leethegasman]

you didnt say that earlier ( going for a proper bite here)🙂

I don't mined taking the bait and won't report you for picking on me.

 

[lame plumber]

only picking up on the content of the posts🙂

 

[tamz]

5.4 NEW EXTENSIONS/ALTERATIONS TO EXISTING INSTALLATIONS
Before commencing the new work, the existing installation shall be tightness tested in accordance with clause 5.3.2 and any permissible pressure drop over the 2 minute test period noted (see also Sub-Section 4.2).
Upon completion of the work to the existing system, the tightness test shall be repeated and the pressure loss after the 2 minute test period shall be no greater than that previously measured and there shall be no smell of gas.

You only "need" to do what you "need" to do. Whether you choose to work above the requirements is up to you and perhaps your wallet or conscience.

Put the scenario into a bit perspective here and think about it. How much gas would be released from a 2mb drop?
Cleverer people than us do some fancy sums and decide what would be safe or not safe. When they come up with what they think is a safe figure, we are talking really safe. Not about half of what would cause the house to blow up. We are talking many many times more on the safe side.

Since i don't need to get up in the morning and there is nothing worth watching on the telly, here is a sum (or calculation if you like that word better) that shows the amount of gas that would be released into a room with a 2mb drop.
The formula for working this out is
LR (leakage rate) = F3 (some clever people worked that out and it is a constant for the type of fuel) X GM (gauge movement) X IV (installation volume) ÷ TTD (tightness test duration)
stick some numbers in and
LR = 0.059 (a constant number for ng) X 2 (the gauge dropped 2mb) x 0.02 (a guess on the big side on this one) ÷ 2 (test time)
LR = 0.00236 ÷ 2 = 0.00118m³/hr


Now think of the EL's of ng, volume of any small space a pipe is allowed to pass through without being vented and think about the number of air changes that occur in an average domestic space.

I know how i would treat this (providing there "IS" no smell) without blinking an eye this but i know how to do fancy sums too and so do you now if you remember it.

Maybe this should be moved to the gsr section

 

[Dotty]

I'd be doing the same calculation as you Tam, but only because that's what I learned with the commercial side.

To me a 2mbr drop on 2m of pipe would set the alarms off rather than it would on a 30m run because of the Iv.

Not comfortable with this in open forum either but it is useful for the new guys sitting their ACS so I'll shift it to the arms.

 

[Mike Jackson]

There's lots of talk of what the book says and what trainers have said but how many answering the original question have

1. Read the original question properly and

2. Read IGEM-UP-1B Ed3

The question is what is the legal requirement, not best practice or what your Auntie Hilda says.

The actual wording of the relevant paragraphs is

For all new installations (with or without appliances connected) or existing installations where no appliances are connected, if there is no perceptible movement (fall) of the gauge reading and there is no smell of gas the installation shall be deemed to have passed the test. Otherwise, the installation shall be deemed to have failed the test.

For existing installations where appliances are connected, if the pressure drop does not exceed the values given in table 3 and there is no smell of gas, the installation shall be deemed to have passed the test. Otherwise, the installation shall be deemed to have failed the test.

The inference is that the drop must be through an appliance but nowhere does it state that you need to prove this. It may be good practice to go beyond the legal requirement but you could be landing yourself in hot water by doing so. Suppose you carry out a LL check and find a 3 mbar drop. Being the concientious engineer that you are you go round and isolate all of the appliances and the drop is still there. You are now legally obliged to rectify the leak or make it safe. Unabgle to find the leak you disc the meter and leave the tenant with no heating, hot water or cooking facilities. The landlord goes ape and sues you. You may feel that you were doing the right thing but, legally, you have exceeded the legal requirement.

The correct method of dealing with the situation is to ask the tenant if they have noticed a smell of gas within the property and then proceed further if they say yes. 9 times out of 10 the tenant will reply in the affirmative and that is when you start isolating stuff to locate the source of the leak.

Before getting to this stage I'll normally give the meter unions a quick tweak as I find most small drops are slight weeps on the meter unions or at the outlet of the ECV.

 

[Kyle87]

Better to ask customer if they ever smell gas before you start any work.
They will say no if its true.
The second your looking for a leak they miraculously can smell gas and walk round the house sniffing like a dog.

 

[dave1]

I agree with mike, ask the cust before you start if they ever smell gas, then if its permissible drop then it is what it says on the tin "permissible"

What everyone considers good practice and safe practice is up to them regarding isolating appliances. Although I would ask the owners permission first.