Sphere shelf life?
Moderator: RichardW
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smashymike
Sphere shelf life?
Just been clearing my garage up after disc/pad change on missus's Xsara and found a couple of new (about 1yr) spheres, two rear and antisink, which i'd not yet got round to fitting. Question is, would they still be ok to fit at 1yr old, they obviously 'look' like new and more than likely woill be mucho better than whats on the Xant but i've got this niggle about putting the effort in and not getting as much out of them? Anyone any advice ?
Not 20 years. More like 3 years.
Their shelf life is "infinite" in the sense that no damage happens to the sphere when sitting on the shelf, and *provided* that they are regassed before use (if they have lost significant gas) they will be fine.
But sitting on the shelf for a long time they will gradually lose gas pressure, and if you then proceed to put them in service with very low gas pressure, they will last only a short time before the diaphram is damaged. (Quite apart from the fact that the ride will be awful too)
It also depends on whether they're the long life multilayer diaphrams or not. (Found on some Xantia and XM front spheres - the ones with the 3 dimples at the end)
For standard spheres, sitting on the shelf for one year would be fine. Anything more than 2 or 3 years however, I would be pressure testing them before using them to check they're ok.
For the long life types anything up to about 4 years on the shelf is fine with no noticable loss of gas, but 5 years or more and I would be pressure testing them before using them.
Regards,
Simon
Their shelf life is "infinite" in the sense that no damage happens to the sphere when sitting on the shelf, and *provided* that they are regassed before use (if they have lost significant gas) they will be fine.
But sitting on the shelf for a long time they will gradually lose gas pressure, and if you then proceed to put them in service with very low gas pressure, they will last only a short time before the diaphram is damaged. (Quite apart from the fact that the ride will be awful too)
It also depends on whether they're the long life multilayer diaphrams or not. (Found on some Xantia and XM front spheres - the ones with the 3 dimples at the end)
For standard spheres, sitting on the shelf for one year would be fine. Anything more than 2 or 3 years however, I would be pressure testing them before using them to check they're ok.
For the long life types anything up to about 4 years on the shelf is fine with no noticable loss of gas, but 5 years or more and I would be pressure testing them before using them.
Regards,
Simon
Simon
1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White
2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
1998 Xantia S2 3.0 V6 Auto Exclusive
1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White
2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
1998 Xantia S2 3.0 V6 Auto Exclusive
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smashymike
In my opinion, I would reckon the "shelf life" theory is more theoretical than factual.
I bought a set of 'new' spheres for my BX16V in 2001 from a guy who bought them in the UK in 1994; I put them on the car and they are still there to this day.
More recently, I was collecting a few bits off a CX that had sat in a garage for about 12 years and I commented that the spheres had never been regassed due to no signs of grinding on the charging nipples and expressed surprise that he had just left them on the wreck. The owner siad they were left there due to being impossible to remove them and told me if I could get them off, I could have them for free. I had no tools on me and he had a limited supply, but I grabbed a claw hammer, gave them a couple of hits and wound them off. Tested they showed still charged, so we regassed them and fitted them to my sons BX. That was over 2 years ago and they are still going.
Maybe I have been just lucky, but personally, I think if the new spheres are kept sealed there's little chance of too much deterioration and if left in a car, again, no air or contaminents can get to anything that is likely to cause them to deteriorate.
No doubts life expectancy would be reduced to some extent, but not as drastically as in theory it may first seem.
A few tips on changing rear spheres will be found here.
http://www.frenchcarforum.co.uk/forum/v ... php?t=1695
Alan S
I bought a set of 'new' spheres for my BX16V in 2001 from a guy who bought them in the UK in 1994; I put them on the car and they are still there to this day.
More recently, I was collecting a few bits off a CX that had sat in a garage for about 12 years and I commented that the spheres had never been regassed due to no signs of grinding on the charging nipples and expressed surprise that he had just left them on the wreck. The owner siad they were left there due to being impossible to remove them and told me if I could get them off, I could have them for free. I had no tools on me and he had a limited supply, but I grabbed a claw hammer, gave them a couple of hits and wound them off. Tested they showed still charged, so we regassed them and fitted them to my sons BX. That was over 2 years ago and they are still going.
Maybe I have been just lucky, but personally, I think if the new spheres are kept sealed there's little chance of too much deterioration and if left in a car, again, no air or contaminents can get to anything that is likely to cause them to deteriorate.
No doubts life expectancy would be reduced to some extent, but not as drastically as in theory it may first seem.
A few tips on changing rear spheres will be found here.
http://www.frenchcarforum.co.uk/forum/v ... php?t=1695
Alan S
RIP Sept 19th 2008.
She said "Put the cat out" She didn't mention it was on fire!!
She said "Put the cat out" She didn't mention it was on fire!!
Hi all,
I have read a lot of debate on this subject and widely differing views. Without wishing to offend here is mine:
When the sphere is on the shelf the diaphragm inside is completely pressed flat against the inside surface of the steel sphere. The diaphagm only occupies the lower half of the sphere, the top have being bare steel. The pressurised gas is pushing against all of the surfaces inside the sphere equally. The bottom part of the diaphragm has a hard plastic disc attached just where it passes over the orifice in the threaded part of the neck. The diaphragms are made of nitrile rubber compounds. At a molecular level the gas molecules will eventually pass through the diaphragm material just like a ballon which deflates after a while. However, this would only be the case if there was air on the other side of the diaphragm. When the sphere is on the shelf and the diaphragm is pressed against the inside steel surface then the migration of molecules is halted at the steel/rubber interface. Whilst it is not impossible for the gas molecules to pass through the steel this would take 10 orders of magnitude longer than through the rubber (due to the relative permeability of both materials). In which case the gas molecules may migrate through the rubber but they can't get any further than the steel surface. The only part of the diaphragm with contact to the outside air is the part above the orifice. At this point the diaphragm is thicker and capped with a hard plastic disc.
The only other part of the sphere which has the potential to leak is at the filler plug. Beneath the plug top there's a groove containing an o-ring. Its the o-ring which does the sealing.
When the sphere is in use the outside of the diaphragm is now no longer pressed against the inside steel surface of the sphere. The interface is now between the rubber and the LHM fluid. In this case the migrating molecules of gas passing through the diaphragm are able to escape into the fluid and be carried away back to the reservoir finally escaping to the atmosphere.
Overall my opinion is that the on-shelf sphere life is much greater than suggested above and previous writings on the same subject. The escape route for the gas is extremely limited. However, in use, the gas pressure will reduce as fast as the molecules can find their way though the molecular structure of the rubber.
I am not suggesting however that the pressure should not be checked before fitting the spheres to your vehicle. That simply constitutes good engineering practice.
Cheers
noz 8)
I have read a lot of debate on this subject and widely differing views. Without wishing to offend here is mine:
When the sphere is on the shelf the diaphragm inside is completely pressed flat against the inside surface of the steel sphere. The diaphagm only occupies the lower half of the sphere, the top have being bare steel. The pressurised gas is pushing against all of the surfaces inside the sphere equally. The bottom part of the diaphragm has a hard plastic disc attached just where it passes over the orifice in the threaded part of the neck. The diaphragms are made of nitrile rubber compounds. At a molecular level the gas molecules will eventually pass through the diaphragm material just like a ballon which deflates after a while. However, this would only be the case if there was air on the other side of the diaphragm. When the sphere is on the shelf and the diaphragm is pressed against the inside steel surface then the migration of molecules is halted at the steel/rubber interface. Whilst it is not impossible for the gas molecules to pass through the steel this would take 10 orders of magnitude longer than through the rubber (due to the relative permeability of both materials). In which case the gas molecules may migrate through the rubber but they can't get any further than the steel surface. The only part of the diaphragm with contact to the outside air is the part above the orifice. At this point the diaphragm is thicker and capped with a hard plastic disc.
The only other part of the sphere which has the potential to leak is at the filler plug. Beneath the plug top there's a groove containing an o-ring. Its the o-ring which does the sealing.
When the sphere is in use the outside of the diaphragm is now no longer pressed against the inside steel surface of the sphere. The interface is now between the rubber and the LHM fluid. In this case the migrating molecules of gas passing through the diaphragm are able to escape into the fluid and be carried away back to the reservoir finally escaping to the atmosphere.
Overall my opinion is that the on-shelf sphere life is much greater than suggested above and previous writings on the same subject. The escape route for the gas is extremely limited. However, in use, the gas pressure will reduce as fast as the molecules can find their way though the molecular structure of the rubber.
I am not suggesting however that the pressure should not be checked before fitting the spheres to your vehicle. That simply constitutes good engineering practice.
Cheers
noz 8)
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Hi Norrie - long time no see 8)
Thats the best description I've ever heard up until now on the N-gas diffusion (not !) on dorming spheres. It perfectly explains why old (but still un-used & boxed) spheres have worked as they should.
The only weak point I find in your description is the part where the N-gas would diffuse out - into the LHM.
If there is ANY LHM present inside the sphere to contact the membrane - there is also absolutely no pressure difference between the N-gas and the LHM on each side of the membrane. So why would any diffusion take place at all ?
Thats the best description I've ever heard up until now on the N-gas diffusion (not !) on dorming spheres. It perfectly explains why old (but still un-used & boxed) spheres have worked as they should.
The only weak point I find in your description is the part where the N-gas would diffuse out - into the LHM.
If there is ANY LHM present inside the sphere to contact the membrane - there is also absolutely no pressure difference between the N-gas and the LHM on each side of the membrane. So why would any diffusion take place at all ?
Anders (DK) - '90 BX16Image
Hi Anders,
Thanks. I've been busy for a while now so not so much spare time to go around.
Sorry to get a bit boringly technical but here's the answer to your question:
When we talk about pressure we are actually talking about 'total' pressure. The atmosphere is made up of many different gasses in different amounts. Each gas has its own 'partial' pressure. The total pressure is the arithmetic addition of all the partial pressures (Boyles Law). The driving force for mass transfer through the membrane is not the difference in total pressure but the difference in partial pressure of the gas you are speaking about, in this case Nitrogen. There is only a very small amount of dissolved nitrogen in the LHM fluid and so therefore the partial pressure is very low. Assuming that the nitrogen is pure inside the sphere then the partial pressure = the total pressure (ie very high). The driving force which pushes the gas through the membrane is the difference between the two partial pressures.
As an example, consider a bottle of fizzy pop like coke. The gas which makes it fizzy is CO2 and is dissolved in the fluid under pressure. Now open the bottle and pour out half the liquid and quickly seal the bottle again. The space above the bottle will re-pressurise after a short while but the coke will eventually go 'flat' even if you don't take out any more liquid. The reason is that the air which entered the bottle to replace the leaving fluid had only a small amount of CO2 (low partial pressure) within it. The remaining liquid contained dissolved CO2 (high partial pressure). Mass exchange takes place at the surface of the fluid until both the air and the liquid contain the same amount of CO2 (ie CO2 leaves the fluid and enters the space above). The liquid, having lost most of its CO2, appears to have lost it's 'fizz' because the CO2 is no longer dissolved in the liquid.
Anorak safely stowed in the coat cupboard now.
Cheers
noz 8)
Thanks. I've been busy for a while now so not so much spare time to go around.
Sorry to get a bit boringly technical but here's the answer to your question:
When we talk about pressure we are actually talking about 'total' pressure. The atmosphere is made up of many different gasses in different amounts. Each gas has its own 'partial' pressure. The total pressure is the arithmetic addition of all the partial pressures (Boyles Law). The driving force for mass transfer through the membrane is not the difference in total pressure but the difference in partial pressure of the gas you are speaking about, in this case Nitrogen. There is only a very small amount of dissolved nitrogen in the LHM fluid and so therefore the partial pressure is very low. Assuming that the nitrogen is pure inside the sphere then the partial pressure = the total pressure (ie very high). The driving force which pushes the gas through the membrane is the difference between the two partial pressures.
As an example, consider a bottle of fizzy pop like coke. The gas which makes it fizzy is CO2 and is dissolved in the fluid under pressure. Now open the bottle and pour out half the liquid and quickly seal the bottle again. The space above the bottle will re-pressurise after a short while but the coke will eventually go 'flat' even if you don't take out any more liquid. The reason is that the air which entered the bottle to replace the leaving fluid had only a small amount of CO2 (low partial pressure) within it. The remaining liquid contained dissolved CO2 (high partial pressure). Mass exchange takes place at the surface of the fluid until both the air and the liquid contain the same amount of CO2 (ie CO2 leaves the fluid and enters the space above). The liquid, having lost most of its CO2, appears to have lost it's 'fizz' because the CO2 is no longer dissolved in the liquid.
Anorak safely stowed in the coat cupboard now.
Cheers
noz 8)
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smashymike
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Kowalski
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Not that I want to pour water on your theory too much here because the theory is correct but rather because I'm not sure whether it applies or not.noz wrote:When we talk about pressure we are actually talking about 'total' pressure. The atmosphere is made up of many different gasses in different amounts. Each gas has its own 'partial' pressure. The total pressure is the arithmetic addition of all the partial pressures (Boyles Law). The driving force for mass transfer through the membrane is not the difference in total pressure but the difference in partial pressure of the gas you are speaking about, in this case Nitrogen. There is only a very small amount of dissolved nitrogen in the LHM fluid and so therefore the partial pressure is very low. Assuming that the nitrogen is pure inside the sphere then the partial pressure = the total pressure (ie very high). The driving force which pushes the gas through the membrane is the difference between the two partial pressures.
If the LHM was in contact with the Nitrogen, I'd have no doubt about agreeing with you but there is a rubber membrane between the two. I'm not sure whether diffusion of gases through rubber membranes is quite covered by Boyle's writings
I was wondering the same thing too....Kowalski wrote:Not that I want to pour water on your theory too much here because the theory is correct but rather because I'm not sure whether it applies or not.
If the LHM was in contact with the Nitrogen, I'd have no doubt about agreeing with you but there is a rubber membrane between the two. I'm not sure whether diffusion of gases through rubber membranes is quite covered by Boyle's writings
Clearly the gas does gradually escape through the diaphram, but the mechanism by which it does is still not proven in this thread IMHO.
I dont think the filler plug seal is a significant source of leakage as the multilayer diaphram spheres keep their gas pressure so much longer when the only change is the diaphram itself.
The only way to prove it would be to buy two identical spheres, use one on a car for years, and keep the other one on the shelf and measure their pressures...
Regards,
Simon
Simon
1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White
2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
1998 Xantia S2 3.0 V6 Auto Exclusive
1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White
2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
1998 Xantia S2 3.0 V6 Auto Exclusive
Hi all,
Thanks for the replies and your interest in this subject.
Kowalski,
Water desalination plants for making drinking water out of sea water use a process known as 'Reverse Osmosis'. This is where the natural transfer of clean water (low salt concentration) through the membrane into the salt water (high salt concentration) is reversed by overcoming the osmotic pressure by the application of an external source of pressure in the opposite direction (usually by a high pressure pump). In the case of the sphere the 'total' pressure difference is acting in the same direction as the 'osmotic' pressure difference with reference to the Nitrogen.
Simon,
Thanks for your replies. Hopefully if we reach a conclusion through reasoned argument we can put to bed some of the more 'flowery' theories which abound on this subject. Thanks.
Cheers
noz 8) [/quote]
Thanks for the replies and your interest in this subject.
Kowalski,
Maybe I didn't explain myself well enough. Boyles Law was quoted to emphasise the fact that total pressure is the summation of the partial pressures of all the component gases, nothing more. The movement of gases through a membrane is called the process of 'Osmosis'. (For example, Osmosis is the process by which gases (Oxygen and Carbon Dioxide) are exchanged across a membrane (lungs) in different directions, driven by osmotic pressure.) Osmotic pressure (or difference in pressure) is the driving force for mass transfer through any membrane. The rate of transfer is a function of partial (osmotic) pressure difference and the permeability of the membrane. If Citroen have changed the membrane material because they think it 'leaks' too fast then it is the permeability which they are changing.If the LHM was in contact with the Nitrogen, I'd have no doubt about agreeing with you but there is a rubber membrane between the two. I'm not sure whether diffusion of gases through rubber membranes is quite covered by Boyle's writings
Water desalination plants for making drinking water out of sea water use a process known as 'Reverse Osmosis'. This is where the natural transfer of clean water (low salt concentration) through the membrane into the salt water (high salt concentration) is reversed by overcoming the osmotic pressure by the application of an external source of pressure in the opposite direction (usually by a high pressure pump). In the case of the sphere the 'total' pressure difference is acting in the same direction as the 'osmotic' pressure difference with reference to the Nitrogen.
Simon,
Hopefully the above has made you change your opinion.Clearly the gas does gradually escape through the diaphram, but the mechanism by which it does is still not proven in this thread IMHO.
Thanks for your replies. Hopefully if we reach a conclusion through reasoned argument we can put to bed some of the more 'flowery' theories which abound on this subject. Thanks.
Cheers
noz 8) [/quote]
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Its been a long time since I did chemistry but I seem to remember a caveat of the ideal gas laws- they are an approximation of real gases. In the real world ideal gases do not exist as there are interactions between the molecules not defined by the ideal gas laws.
I remember very clearly a Chem practical that did not work, the tutor told me that the laws we had learnt (Ideal Gas laws) did not always work in the real world. All would be revealed in Chem II!!!!
Disclaimer:
Chemistry never made any sense to me and as I didn't need it I never found out the secrets of Gas Interactions.
regards
sean
I remember very clearly a Chem practical that did not work, the tutor told me that the laws we had learnt (Ideal Gas laws) did not always work in the real world. All would be revealed in Chem II!!!!
Disclaimer:
Chemistry never made any sense to me and as I didn't need it I never found out the secrets of Gas Interactions.
regards
sean
1996 XM 2.1 TD exclusive