Running gas pipe

[Agile]

No competent installer would make such a mess of the soldering to have any negligable effect on flow IMO. If this is an issue for you, rather than opt for compression fittings opt for someone competent to do the work for you instead.
MW

I think that you have missed the point here. We often go to existing installations where we have no control over who did it or how it was done. In that case it often becomes obvious that the measured pressure drop is a lot more then the calculations give, sometimes 50-70%.

We are not in a position to open up the pipework to inspect it. Often we go to faults caused by lack of adequate gas pressure and find solder, jointing compound or PTFE tape blocking the joints.

Although it seems counter intuitive to me at the moment I will have to accept that a 22/28 has more resistance than a 28/22.

However could Sanj please suggest the possible resistance of a 22/28 compared with an elbow and the similar 28/22 transition to put this into perspective in the gas supply perspective.

I dont see a 1mB pressure drop in 21 mB as indicating a pipe coming close to its maximum flow capacity in a domestic situation.

Tony

 

[Garthzog]

I've seen some installs where 22mm has come out of the existing pipework near the meter to a new gas valve, and the pipework has gone to 28mm after that. That has already been suggested here and sounds like a good option for ease of getting from the meter to 28mm and a straighter run

The crux of the debate you've followed has been focused on the legitimacy of this ... IMO there is no benefit.

But it was suggested in this thread by someone who is competent/CORGI qualified....

It was said here that quite often solder flow into the pipe can reduce flow

No competent installer would make such a mess of the soldering to have any negligable effect on flow IMO. If this is an issue for you, rather than opt for compression fittings opt for someone competent to do the work for you instead.

MW

The joins I have made that were cut open for inspection during courses have been fine and there were no problems with my previous gas work or current refrigerant work, but this was suggested by someone in this thread who is competent/CORGI registered, so I assume from their experience with competent work that this is the case and one of the reason for pressure drops being greater than calculated. That's why I asked the question.

G

 

[megawatt]

No Tony, you are missing the point ... After reading your post the OP is now considering using compression fittings over correctly fitted soldered couplings to ensure that solder doesn't reduce the flow ... Doh!

We cannot mandate for stupid installers leaving their apprentice stuffed up the pipe and reducing the flow but solder from couplings affecting pressure drop on an otherwise sound and well sized installation ... get real, who are you kidding.

MW

 

[Agile]

"""so I assume from their experience with competent work that this is the case"""

I dont exactly understand what you have meant to say here.

Competently made joints still usually use a pipe cutter which restricts the pipe diameter at joints where the flow disturbance is already quite turbulent.

Much pipework is done by slapdash, lazy or couldn't care less installers.

Just look under a few boilers this week and see how many have dribbles of solder left on the outside of the pipework! Thats the quality of pipework on a high proportion of boilers I see!

Tony

 

[Onetap]

Competently made joints still usually use a pipe cutter which restricts the pipe diameter at joints where the flow disturbance is already quite turbulent.

It should be reamed out to restore the bore to the normal size, so those aren't competently made joints. The turbulence generated by the swaged-down bore can generate enough turbulence to cause erosion and pin-holing with water.

I know of one company that regards a failure to ream copper pipe out after cutting as a dismissible offence; it's not in the UK.

 

[Agile]

I agree that it should be done, but I dont think that I have even seen a tool sold specifically for 15/22/28 copper tube!

Does BES have them?

If the pipe cutter wheel is worn then the indentation is even greater!

Tony

 

[gas4you]

The old manual pipe cutters used to use the tapered end to do this.

 

[ChrisR]

I find those tapered ends very poor. A deburring tool (screwfix etc) works well but I find a sharp small penknife blade perfect.

Fwiw I have often increased gas pipe size after say it comes up out of the floor in 3/4in barrel, to 28mm where it was all 3/4 barrel before. The decrease in friction, and therefore pressure loss, has always been what I would have expected.

The tables (which are based on a formula I can provide if anyone's interested) are always a long way out. It's nothing to do with bad installation practice - I've tried very hard on long runs without success in achieving the theoretically predicted losses. It may be that the inner surface of the pipe isn't as smooth as the theorists thought.
The error is particularly noticeable with smaller pipe sizes, which I would (intuitively) have expected.

 

[chrishutt]

Fwiw I have often increased gas pipe size after say it comes up out of the floor in 3/4in barrel, to 28mm where it was all 3/4 barrel before. The decrease in friction, and therefore pressure loss, has always been what I would have expected.

Also interesting to note that with steel barrel pipework every bend or tee represents a substantial and sudden increase in the cross sectional area of the pipe (since the bore of the fitting is more or less the same as the OD of the pipe). Yet this doesn't appear to produce an excessive pressure drop. I don't think the pressure drop from an increase in bore can be particularly significant.

 

[Garthzog]

"""so I assume from their experience with competent work that this is the case"""

I dont exactly understand what you have meant to say here.

As gas has to be done only by competent people, I assumed that's who you were referring too. Even if an apprentice had done a poor job, I would have expected the poor flow to be found on commissioning. I can't see anything about using compression fittings over soldered ones in my gas or CORGI notes, but I wondered if that had changed with the more stringent regs after what you'd said.

Competently made joints still usually use a pipe cutter which restricts the pipe diameter at joints where the flow disturbance is already quite turbulent.

I ream mine out to ensure the end is parallel and not burred over or use a saw, even with water pipe.

Much pipework is done by slapdash, lazy or couldn't care less installers.

Exactly why I'd rather do most things myself.

Just look under a few boilers this week and see how many have dribbles of solder left on the outside of the pipework! Thats the quality of pipework on a high proportion of boilers I see!

Tony

I take it that's for older installs rather than new ones?

Cheers

G

 

[Agile]

The tables (which are based on a formula I can provide if anyone's interested) are always a long way out. It's nothing to do with bad installation practice - I've tried very hard on long runs without success in achieving the theoretically predicted losses.

My experience is that the actual loss can vary widely and have concluded that either the furmulae are wrong or the installation defects are to blame.

I visited one where there was a pressure loss of about 12 mB in a newish length of 22 mm tube with about 6 m and five elbows. It was boxed in and I never did find out what the problem was as her builder dealt with it as it was partly under laminate floor!

Tony

 

[megawatt]

Lord Lucan's probably in there ... Or Elvis!

 

[Balenza]

Part of the problem is all the cowboys use fittings to turn corners (in order to cut corners) instead of the former and slide .
Hence the higher pressure drop.

 

[sanj.varah]

I reckon, and this is based on guestimating a lot of variables, a reducer that goes from 22 to 28mm will have the same pressure drop as approx 0.25m of pipe. Going the other way, there should be negligible drop.

As I said this is based on a large number of variables, that i guestimated.

 

[chrishutt]

But Sanj you have to specify which pipe it's equivalent to 0.25 metres of - the 22mm or 28mm! It makes a big difference.