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Stiff gas isolator


blackrose

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I have two gas systems on my boat, one side which I use all the time for the hob and oven and the other side is for a gas fridge and instant gas water heater which I only use when I'm away from shore power (thus not very often!)

 

The main 90 deg turn isolator seems to have gone quite stiff as it hasn't been opened in a while and it feels a bit spongy at either end of the turn. I got the fridge and water heater going today and they're fine but I'm not really sure if the isolator is still working. I guess I should switch it to closed and try to relight the appliances on that system.

 

Also, one thing I've never understood that someone might be able to help me with: if I haven't lit either the fridge or the water heater for a while it takes forever to get the gas from the bottle and down the main run (1/2" and about 14m length) and light the appliances. I always isolate the line in the locker and also isolate both appliances when not in use. So what happens to the gas that was in the pipe. Please note, this issue was happening long before the main isolator started feeling strange. It's always taken ages to purge the line and get fresh gas coming through, even when the system was newly installed.

 

I can only think that once decompressed in gaseous form, the gas in the pipe goes off somehow, whereas the gas in the bottle is fine? I've no idea really.

 

 

 

 

 

Edited by blackrose
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I have no idea where the gas in the pipes goes but it does go and went on the three boats that I have owned. My boats were/are only small, 30 footers, and the gas hob and oven are at the back quite near the gas locker but even if the gas has only been off for a week or so it still takes a while to get to the burners.

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Yes it's weird isn't it. An impermeable gas pipe which is isolated at either end is a vessel full of gas, so what's happening to make the gas disappear over time?

 

No joints in the gas pipe between the locker and the first appliance and no leaks in my system according to the bubble tester (but I don't want to open a whole can of worms there please!)

Edited by blackrose
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It is due to gas pipe leaks. Very small ones, well within the limits of gas leak testing. But over a very long time, the individual molecules of gas inside the pipe, and the individual molecules of air outside the pipe, migrate such that the pipe becomes mostly full of air.

 

We always leave the gas on in our boat so I don’t see the effect there, but in my caravan I see this effect after a few months of non-use.

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4 minutes ago, pete.i said:

I have no idea where the gas in the pipes goes but it does go and went on the three boats that I have owned. My boats were/are only small, 30 footers, and the gas hob and oven are at the back quite near the gas locker but even if the gas has only been off for a week or so it still takes a while to get to the burners.

Propane or  Butane?  Any leaks? What is a while? Regulator been replaced this century?

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9 minutes ago, nicknorman said:

It is due to gas pipe leaks. Very small ones, well within the limits of gas leak testing. But over a very long time, the individual molecules of gas inside the pipe, and the individual molecules of air outside the pipe, migrate such that the pipe becomes mostly full of air.

 

We always leave the gas on in our boat so I don’t see the effect there, but in my caravan I see this effect after a few months of non-use.

Thanks. Interesting...

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17 minutes ago, Tracy D'arth said:

Propane or  Butane?  Any leaks? What is a while? Regulator been replaced this century?

Propane. As I said, no perceptible leaks but according to nicknorman we've all got microscopic leaks. Probably could do with new regulators on both systems. They're 15 years old now but they're both still working. I just checked the isolator and that's still working too - at least it's preventing me from relighting the appliances. I've no other way of testing it.

Edited by blackrose
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With propane you should aim for zero loss through leaks. Gas diffusion through copper pipe is to all intents nil at 37mB pressure. But your flexible hose is another matter, it will be date coded and should be changed every 5 years to be safe. It should also have clench hose clips preferably rather than worm drive clips.

Old regulators can tend to stick closed when pressure is zero for a long period.

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It's leaks.

 

I shut my gas off at the cylinder when I leave the boat.  I can go back a couple of weeks later and without turning the gas on, light a burner on the hob which will burn for a few seconds before fading out.  To me that confirms that I don't have a leak (as long as I haven't got a leak-through on the cylinder tap).

 

When it wouldn't light, I searched, and found, a very slight leak on the regulator.

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The flexible hose from the bottle is on the high pressure side of the isolator. The loss I'm talking about is on the low pressure side of the system from the isolator downstream to the appliances. As I said there is no perceptible loss, so to all intents and purposes if it can't be observed it is zero loss.

 

If Nicknorman is correct (above) then the lost gas that was in the pipe is the result of microscopic leaks over time which all systems are subject to. I haven't used that side of the system for over a year, so that would explain it.

Edited by blackrose
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1 hour ago, blackrose said:

The flexible hose from the bottle is on the high pressure side of the isolator. The loss I'm talking about is on the low pressure side of the system from the isolator downstream to the appliances. As I said there is no perceptible loss, so to all intents and purposes if it can't be observed it is zero loss.

 

If Nicknorman is correct (above) then the lost gas that was in the pipe is the result of microscopic leaks over time which all systems are subject to. I haven't used that side of the system for over a year, so that would explain it.

I wouldn’t say that these leaks are inevitable, just that they commonly exist and are too small to be detected eg at BSS check. The BSS check, whether by bubble tester or manometer, only detects a leak that would manifest itself in a few minutes. By comparison, if you have left that gas system untouched for a year (which is ~ half a million minutes) it can’t be too surprising that some leakage has happened. It should in theory at least be possible to eliminate that leak as Dor mentions - if you are that desperate to!

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2 minutes ago, nicknorman said:

I wouldn’t say that these leaks are inevitable, just that they commonly exist and are too small to be detected eg at BSS check. The BSS check, whether by bubble tester or manometer, only detects a leak that would manifest itself in a few minutes. By comparison, if you have left that gas system untouched for a year (which is ~ half a million minutes) it can’t be too surprising that some leakage has happened. It should in theory at least be possible to eliminate that leak as Dor mentions - if you are that desperate to!

Surely you'd have to be able to detect the leak before you can eliminate it? I've sprayed every joint in the system before and couldn't see any detectable leaks but I'll certainly do it again to make sure.

1 hour ago, dor said:

It's leaks.

 

I shut my gas off at the cylinder when I leave the boat.  I can go back a couple of weeks later and without turning the gas on, light a burner on the hob which will burn for a few seconds before fading out.  To me that confirms that I don't have a leak (as long as I haven't got a leak-through on the cylinder tap).

 

.

I think I could relight the appliances straight away if it was just left for a couple of weeks. I'm talking about leaving it for over a year.

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You have a separate gas tap? I thought you were referring to the bottle valve  when you said isolator.  Your "leak" could well be your gas tap that leaks only when off from the downstream side. Try disassembling it and greasing with Molycote on reassembly.  

Cooker gas taps will also leak minutely after many years use if not greased.  Gas leaks don't have to be at pipe connections.

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You cannot eliminate every leak.  Only make sure that they are not of dangerous proportions.  The main source is flexible pipes.  These are inevitably permeable, and they get worse with age.  Hence the recommendation to change them at 5 years old.  Other 'leaks' which cannot be prevented entirely are at appliance taps and isolation valves.  There has to be clearance in the moving parts of these,  or they would not move.  This clearance is big enough for the gas molecules to slowly diffuse through and be replaced by air.  You could diminish the diffusion even further by regularly dismantling taps etc.and lubricating with the right grease, except that regular dismantling is as likely to make things worse as better  and encourages the not competent to get involved.

 

Dor's check above is a good one, and probably more sensitive than a bubble tester.   Not all that practicable for a liveaboard though.  However you do it, and a manometer is the most sensitive method,  a regular leak check of your gas system is a Good Thing.  Given the price of Propane bottles it may even save you some money.

N

 

PS If you think LPG leaks are difficult, try keeping Helium where you want it to stay.

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12 hours ago, Tracy D'arth said:

Propane or  Butane?  Any leaks? What is a while? Regulator been replaced this century?

Don't know don't care, just had a BSS done on my latest boat and everything is fine which is good enough for me. Gas still disappears after a while. Maybe you ought to direct your attentions to the OP and stop being inflammatory. But then you have always been like that so nothing new there then. Byee.

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6 minutes ago, pete.i said:

Don't know don't care, just had a BSS done on my latest boat and everything is fine which is good enough for me. Gas still disappears after a while. Maybe you ought to direct your attentions to the OP and stop being inflammatory. But then you have always been like that so nothing new there then. Byee.

What? Sorry if you misread my message, I was simply asking for more info. Please don't get upset, I replied with the best of intentions trying to help.

Leaks can be very small, butane evaporates at a lower temperature,  I did not know how long you left the gas off for and regulators do age and stick if 20 years old.

I am not inflammatory but I could take your response as being, but I didn't did I?

Why so nasty?

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1 hour ago, Tracy D'arth said:

What? Sorry if you misread my message, I was simply asking for more info. Please don't get upset, I replied with the best of intentions trying to help.

Leaks can be very small, butane evaporates at a lower temperature,  I did not know how long you left the gas off for and regulators do age and stick if 20 years old.

I am not inflammatory but I could take your response as being, but I didn't did I?

Why so nasty?

Actually the boiling point of propane is lower than that of butane.

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3 hours ago, Tracy D'arth said:

You have a separate gas tap? I thought you were referring to the bottle valve  when you said isolator.  Your "leak" could well be your gas tap that leaks only when off from the downstream side. Try disassembling it and greasing with Molycote on reassembly.  

Cooker gas taps will also leak minutely after many years use if not greased.  Gas leaks don't have to be at pipe connections.

Yes I have an isolator between the regulator and bubble tester on each system (twin systems) in the gas locker. The leak (if indeed it can be classed as such) might be through the gas tap but then it would have to be gas going back through the bubble tester into the regulator from the low pressure side back into the high pressure side. Is that possible?

2 hours ago, Alan de Enfield said:

 

I suppose an analogy is balloons.

 

If rubber wasn't porous to gases then balloons would stay inflated 'for ever' instead of just a couple of days, a gas-hose has a considerably greater wall thickness so the gas-escape is much, much slower than a balloon, but, a gas hose will 'leak'.

Which is why pigtails are in the locker I suppose. This is the view looking into the gas locker. Yes I know it's not supposed to be used for storage of other junk... The wooden blocks are there to help prevent the bottles hitting the regulators as they're pulled out and dropped down. Can my main isolators be serviced? They don't look like they come apart to me. Perhaps I'll just replace them at the same time as the regulators and pigtails.

 

IMG_20210109_112752.jpg

Edited by blackrose
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26 minutes ago, Chewbacka said:

Actually the boiling point of propane is lower than that of butane.

My error, I was so taken aback by pete.i's comment that I rushed a reply. Did my reply seem "inflamatory" to anyone else? Odd really because the freezing point of butane is higher than propane. Stands to reason when you think about it.

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The new kit comes with a test point on the main isolator which would be handy as I'm currently reliant on the bubble testers. I don't have test points on my isolators currently.

 

Will an inspector be able to use the test point if there is bubble tester just downstream?

 

image.png.a4a88767e79a0683ca0ee79a956c513a.png

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8 minutes ago, Alan de Enfield said:

If your gas pipe is dated 04/04 then it should be replaced.

The Industry 'guidance is every 5 years (and 10 years for regulators)

 

It is something we have to do on the Caravan park to keep the insurance valid.

 

 

Technical Advice | Dixons of Westerhope

 

That must be the date of manufacture? I installed the system in 2006 I think. They must be the original ones! ? I guess my last inspector missed it.

 

What's the replacement guidance from Alde on the bubble testers? - mine still look like in good condition. I googled it but can't find anything.

Edited by blackrose
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