I'm in the habit of re-gassing my own spheres. I built the kit to do it about 10 years ago and have re-gassed many spheres. I realise with sphere prices at an all time low this might seem uneconomic but I have the kit and I can so therefore I do.
I was working on my newly acquired CX 22 TRS last weekend. I took the front sphere's off and put them in the rig to test for residual pressure. One read 10 bar and the other read 20 bar. To me this is not unusual as it was probably 10 years ago the car had it's spheres changed despite having an extensive , Citroen, service history.
I removed the plug on the top of each sphere and attempted to re-gas as normal. Unfortunately when I admitted the gas to the sphere it came out the other end as fast as I could put it in.
This again is not entirely unusual. I have had a few sphere's in the past which were dud and wouln't re-gas. The strange thing here is that I drove the car back home from Eastbourne on the UK south coast all the way back to Scotland. The ride wasn't too bad. When I took the sphere's off, I tested them for pressure and there was some left.
How could I have driven nearly 700 miles and tested the spheres only to find that they wouldn't hold pressure when trying to recharge them?
I did see a sphere cut in half once at the Citroen Car Club Rally in Stirling. At the top of the sphere looking from the inside, it had been deliberately manufactured with a couple of spikes at the point where the plug scrrews in. It appeared that, as the pressure became lower in the sphere, one day as you pass over a bump, the diaphragm rises too far and hits the spikes, puncturing the membrane. The remaining gas passes through the resulting hole and makes your LHM reservoir all foamy. Needless to say, once the gas has disappeared the ride is solid.
I also saw that the diaphragm has a solid plastic disc at the very centre. I assumed that this part of the diaphragm is subject to the most stress and the disc protects it. When a sphere is completely at rest e.g. if you have it in your hand, then the gas pressure will push the diaphragm fully downwards against the inside of the sphere. The diaphragm is not unduly stressed since the steel sphere provides an opposing force for the majority of the diaphragm surface. At the outlet hole at the bottom however there is no steel sphere and therefore the diphragm must bridge the hole. At this point there's 70 bar difference across the rubber. I think the plastic disc gives the diphragm the necessary strength for this reason.
Does anyone know why a perfectly working sphere which tested for a reasonable residual pressure should suddenly appear burst when re-gassing?
I've never managed to find out how the diaphragm is bonded to the inside of the sphere. Does anyone know how this is done?
Cheers
noz
Sphere regassing troubles
Moderator: RichardW
OK noz, I'll do the best I can.
As a rule of thumb, any sphere that is allowed to fall to 50% or less of its working pressure is always going to be a debatable proposition when it comes to regassing.
I recently had one on a 16V that had a strange thing too; it would charge, hold the charge yet show a slight bubbling at the damper hole of LHM. It lasted about 2 years and then I had it regassed after which it went about a month & blew.
As regards the internal membrane, look at it as though it's a balloon. After a balloon has been fully inflated, if an attempt is then made to blow it up to that same pressure again, it busts.
With a sphere that is allowed to go almost flat, the majority of the space (lower half) is then filled with LHM whilst the decreasing space (at the top) is filled with an ever decreasing volume of nitrogen. If left go to until they are say at 30% pressure, the membrane gets stretched by the LHM. When it is regassed, the membrane then is stretched in the opposite direction (towards the bottom) of the sphere. During this flexing caused by the stretching, the mebrane is thinned as the base area is increased and weakened due to the flexing/stretching.
As the nitro is added, it may burst and hence fail to regas or alternatively (as has happened to me on more than one occasion) it may 'just' regas but subsequently burst when the weight of the car/LHM pressure is exerted from the other side.
Hope you can follow that; I know what I mean, finding words to explain is something else.[8)][B)]
Alan S [:D]
As a rule of thumb, any sphere that is allowed to fall to 50% or less of its working pressure is always going to be a debatable proposition when it comes to regassing.
I recently had one on a 16V that had a strange thing too; it would charge, hold the charge yet show a slight bubbling at the damper hole of LHM. It lasted about 2 years and then I had it regassed after which it went about a month & blew.
As regards the internal membrane, look at it as though it's a balloon. After a balloon has been fully inflated, if an attempt is then made to blow it up to that same pressure again, it busts.
With a sphere that is allowed to go almost flat, the majority of the space (lower half) is then filled with LHM whilst the decreasing space (at the top) is filled with an ever decreasing volume of nitrogen. If left go to until they are say at 30% pressure, the membrane gets stretched by the LHM. When it is regassed, the membrane then is stretched in the opposite direction (towards the bottom) of the sphere. During this flexing caused by the stretching, the mebrane is thinned as the base area is increased and weakened due to the flexing/stretching.
As the nitro is added, it may burst and hence fail to regas or alternatively (as has happened to me on more than one occasion) it may 'just' regas but subsequently burst when the weight of the car/LHM pressure is exerted from the other side.
Hope you can follow that; I know what I mean, finding words to explain is something else.[8)][B)]
Alan S [:D]
Hi guys, thanks for the various replies.
G4EIY
I don't know. It puzzles me how they do it from new. I have to mill a couple of dogs in the top of the plug so I can turn it whilst under pressure. I assume the device in the factory seals against the sphere body much further away from the plug than mine thus allowing space for a self-gripping type tool to grab the plug on it's circumference. The pictures will be interesting.
Alans,
First of all, I'd like to point out that I'm anything but an expert on this but I have applied a little bit of logic. I have heard the flexing argument many times on this and other forums but I'm afraid I can't bring myself to believe it.
Consider the status of the sphere when the car has been parked for a few days. The fluid has all leaked back to the reservoir and the gas pressure has pushed the diaphragm flat against the lower half of the sphere wall. Now start the engine. The pump pushes fluid from the reservoir into the system. If you have flat(ish) spheres it takes a long time to rise because a lot of fluid has to be pumped. If you have 'new' spheres the car rises quite quickly. I proved this last weekend beyond any reasonable doubt. The car rose within 10 seconds of closing the PR valve, after I had replaced the two front spheres only. That includes the time to pressurise the accumulator. Before replacing the spheres it took a good 30 - 40 seconds from a flat accumulator to normal height.
During the time the pump is filling the system what is happening? To begin with, the system pressure is zero (on the fluid side). As the fluid is pumped into the pipework the fluid pressure rises. The balance of forces at the struts means that the pressure to overcome the car's weight has not yet been reached. At 10 bar N2 in the spheres the fluid will take the easier of the two paths (either into the strut , raising the body or into the sphere, compressing the gas.) At this stage the easier path is into the sphere. The fluid flows into the sphere. As it does so it increases the pressure on the fluid side of the diaphragm. For arguments sake lets consider the fluid pressure as 11 bar. The fluid will continue to flow into the sphere until the moving diaphragm compresses the gas in front of it until 11 bar is reached. When the fluid pressure and the gas pressure are equal the diaphragm stops moving (Newtons first Law). However at 11 bar the pressure is still not enough to raise the weight of the body so the height corrector keeps admitting fluid to the sphere/strut. Follow the same process as described above for increments of pressure increase. The process continues until the fluid pressure exerted on the strut is enough to overcome the weight of the car and the body starts to rise. As more fluid is pumped into the pipes the car continues to rise.
In relative terms it takes much more time from PR valve close to the first sign of movement than it does from that point to reaching normal height. That's because it takes the first time interval to pump the required volume of fluid into the system, thus compressing the gas until the resulting pressure is high enough to overcome the weight of the car. Once the body starts to rise it only takes relatively a little more fluid to raise the body to the normal position.
When the car has reached normal position the height corrector switches off and no more fluid is admitted to the sphere. At this point let's say it took 80 bar of pressure to overcome the weight of the car. The sphere measured 10 bar gas pressure at the start of this diatribe. Sufficient fluid passed into the sphere to move the diaphragm such that the space left for the gas became smaller and smaller. As such the gas pressure rose as the fluid entered the sphere. Once at the normal height, lets say, to achieve 80 bar gas pressure and therefore fluid pressure the position of the diaphragm needs to be approximately 80% of the distance between the threaded end and the domed end ie more fluid than gas.
Now the body is suspended, floating on a cushion of gas. Almost exactly like lying on your back on a water bed.
Now lean on a front wing. The fluid is incompressible, the height corrector is closed from both additional fluid and the return path to the reservoir. As you put weight on the corner of the car the body sinks under your weight. The fluid which was in the strut has no where to go except into the sphere. As it does so it moves the diaphragm a little more thus increasing the gas/fluid pressure. At the same time the body sinks, the height corrector sees this. The HC admits fluid from the pump into the space between the sphere and the strut. The pressure rises until the additional pressure overcomes your bodyweight and the car rises back to the normal position. To support the additional weight the pressure now needs to be, say, 90bar. The gas pressure in the sphere is now 90 bar because the gas has been compressed into an even smaller space, say 85% of it's travel distance.
Remove your bodyweight from the car. It initially rises because the pressure of the gas/fluid pressure is greater than that required to support the new, lighter weight. The HC sees the increase in height and bleeds fluid back to the reservoir. As it does so the fluid contained in the sphere/strut decreases in volume as does the pressure and the weight on the strut pushes the piston back into the bore. When back at the normal height position the HC closes and we are back to where we started.
For this explanation, the initial sphere pressure started at 10 bar and got up to 90 bar to support the car body and your body weight. The diaphragm moved between 80 and 85% (ie the sphere had a greater volume of fluid than gas.) of it's travel when adding and subtracting your bodyweight from the car.
I won't bore you with all the details again but consider the above process now with a 'new' sphere at an initial pressure of 70 bar (CX Front, 500cc). The same experiment would require the pressure at normal height to be the same as before at 80bar. Thus to achieve this increase in pressure from 70bar only a small amount of fluid needs to be added to the sphere. Therefore the respective movement now seen in the diaphragm position becomes, say, 15-20% ie more gas than fluid.
Sorry to ramble on but I'm coming to my conclusion.
When the car is parked and 'depressurised' the diaphragms are pressed against the lower surface of all the spheres by the respective gas pressure in each of the spheres (no anti-sink in this hypothesis). When the engine is started the fluid is pumped into the pipework and continues until the body reaches the normal height. The time this takes and the volume of fluid required both depend on all the spheres' initial pressures.
When the car is travelling along the road the diaphragms are continually in motion as each change in 'weight' (substitute bumps in the road for adding more bodyweight to the car) requires a respective change in pressure to match the disturbance inputs from the roadwheels. I don't know how much they move in practice but a guess of 15-20% would not be unreasonable in my opinion. This continuous position change will happen at the location in the sphere dictated by the initial pressure. But move it will, and continuously.
Therefore, the sphere doctor
rejects the concept of diaphragm failure due to flexing. The diaphragms flex through most of their permissable range every time you use the car. Your inflated balloon concept is flawed because the balloon is inflated to it's full extent every time you park the car for more than 6 hours. The size of the diaphragm must be such that when the system is fully depressurised and the diaphragm is pressed against the lower half of the sphere, it cannot be stretched at this point. It must be exactly the right size to sit there indefinitely stress-free. At all times in it's life the diaphragm never sees a difference in pressure across the diaphragm itself so it is never stressed. In theory you don't even need a diaphragm. The sphere would work without one as long as the gas was always trapped above the fluid. You only need the diaphragm to keep the gas in the sphere when it's manufactured and in the box. (OK, OK it may also slow down the diffusion of the gas into the fluid, but I'm making a point here)
I concede that if you let the pressure go too low then when you hit a particulary large bump the resultant compression of the gas may cause the diaphragm to hit the top of the sphere and if it has the built in spikes then the diaphragm will be punctured rendering it useless.
No offence intended to anyone. If any of my argument is in doubt, please feel free to humiliate me in public. I have the stocks ready.
cheers
norrie
ps in case you are wondering, I just made the whole lot of this up as I was typing. Never thought of it before. Sorry for the inane ramblings.
G4EIY
I don't know. It puzzles me how they do it from new. I have to mill a couple of dogs in the top of the plug so I can turn it whilst under pressure. I assume the device in the factory seals against the sphere body much further away from the plug than mine thus allowing space for a self-gripping type tool to grab the plug on it's circumference. The pictures will be interesting.
Alans,
First of all, I'd like to point out that I'm anything but an expert on this but I have applied a little bit of logic. I have heard the flexing argument many times on this and other forums but I'm afraid I can't bring myself to believe it.
Consider the status of the sphere when the car has been parked for a few days. The fluid has all leaked back to the reservoir and the gas pressure has pushed the diaphragm flat against the lower half of the sphere wall. Now start the engine. The pump pushes fluid from the reservoir into the system. If you have flat(ish) spheres it takes a long time to rise because a lot of fluid has to be pumped. If you have 'new' spheres the car rises quite quickly. I proved this last weekend beyond any reasonable doubt. The car rose within 10 seconds of closing the PR valve, after I had replaced the two front spheres only. That includes the time to pressurise the accumulator. Before replacing the spheres it took a good 30 - 40 seconds from a flat accumulator to normal height.
During the time the pump is filling the system what is happening? To begin with, the system pressure is zero (on the fluid side). As the fluid is pumped into the pipework the fluid pressure rises. The balance of forces at the struts means that the pressure to overcome the car's weight has not yet been reached. At 10 bar N2 in the spheres the fluid will take the easier of the two paths (either into the strut , raising the body or into the sphere, compressing the gas.) At this stage the easier path is into the sphere. The fluid flows into the sphere. As it does so it increases the pressure on the fluid side of the diaphragm. For arguments sake lets consider the fluid pressure as 11 bar. The fluid will continue to flow into the sphere until the moving diaphragm compresses the gas in front of it until 11 bar is reached. When the fluid pressure and the gas pressure are equal the diaphragm stops moving (Newtons first Law). However at 11 bar the pressure is still not enough to raise the weight of the body so the height corrector keeps admitting fluid to the sphere/strut. Follow the same process as described above for increments of pressure increase. The process continues until the fluid pressure exerted on the strut is enough to overcome the weight of the car and the body starts to rise. As more fluid is pumped into the pipes the car continues to rise.
In relative terms it takes much more time from PR valve close to the first sign of movement than it does from that point to reaching normal height. That's because it takes the first time interval to pump the required volume of fluid into the system, thus compressing the gas until the resulting pressure is high enough to overcome the weight of the car. Once the body starts to rise it only takes relatively a little more fluid to raise the body to the normal position.
When the car has reached normal position the height corrector switches off and no more fluid is admitted to the sphere. At this point let's say it took 80 bar of pressure to overcome the weight of the car. The sphere measured 10 bar gas pressure at the start of this diatribe. Sufficient fluid passed into the sphere to move the diaphragm such that the space left for the gas became smaller and smaller. As such the gas pressure rose as the fluid entered the sphere. Once at the normal height, lets say, to achieve 80 bar gas pressure and therefore fluid pressure the position of the diaphragm needs to be approximately 80% of the distance between the threaded end and the domed end ie more fluid than gas.
Now the body is suspended, floating on a cushion of gas. Almost exactly like lying on your back on a water bed.
Now lean on a front wing. The fluid is incompressible, the height corrector is closed from both additional fluid and the return path to the reservoir. As you put weight on the corner of the car the body sinks under your weight. The fluid which was in the strut has no where to go except into the sphere. As it does so it moves the diaphragm a little more thus increasing the gas/fluid pressure. At the same time the body sinks, the height corrector sees this. The HC admits fluid from the pump into the space between the sphere and the strut. The pressure rises until the additional pressure overcomes your bodyweight and the car rises back to the normal position. To support the additional weight the pressure now needs to be, say, 90bar. The gas pressure in the sphere is now 90 bar because the gas has been compressed into an even smaller space, say 85% of it's travel distance.
Remove your bodyweight from the car. It initially rises because the pressure of the gas/fluid pressure is greater than that required to support the new, lighter weight. The HC sees the increase in height and bleeds fluid back to the reservoir. As it does so the fluid contained in the sphere/strut decreases in volume as does the pressure and the weight on the strut pushes the piston back into the bore. When back at the normal height position the HC closes and we are back to where we started.
For this explanation, the initial sphere pressure started at 10 bar and got up to 90 bar to support the car body and your body weight. The diaphragm moved between 80 and 85% (ie the sphere had a greater volume of fluid than gas.) of it's travel when adding and subtracting your bodyweight from the car.
I won't bore you with all the details again but consider the above process now with a 'new' sphere at an initial pressure of 70 bar (CX Front, 500cc). The same experiment would require the pressure at normal height to be the same as before at 80bar. Thus to achieve this increase in pressure from 70bar only a small amount of fluid needs to be added to the sphere. Therefore the respective movement now seen in the diaphragm position becomes, say, 15-20% ie more gas than fluid.
Sorry to ramble on but I'm coming to my conclusion.
When the car is parked and 'depressurised' the diaphragms are pressed against the lower surface of all the spheres by the respective gas pressure in each of the spheres (no anti-sink in this hypothesis). When the engine is started the fluid is pumped into the pipework and continues until the body reaches the normal height. The time this takes and the volume of fluid required both depend on all the spheres' initial pressures.
When the car is travelling along the road the diaphragms are continually in motion as each change in 'weight' (substitute bumps in the road for adding more bodyweight to the car) requires a respective change in pressure to match the disturbance inputs from the roadwheels. I don't know how much they move in practice but a guess of 15-20% would not be unreasonable in my opinion. This continuous position change will happen at the location in the sphere dictated by the initial pressure. But move it will, and continuously.
Therefore, the sphere doctor
rejects the concept of diaphragm failure due to flexing. The diaphragms flex through most of their permissable range every time you use the car. Your inflated balloon concept is flawed because the balloon is inflated to it's full extent every time you park the car for more than 6 hours. The size of the diaphragm must be such that when the system is fully depressurised and the diaphragm is pressed against the lower half of the sphere, it cannot be stretched at this point. It must be exactly the right size to sit there indefinitely stress-free. At all times in it's life the diaphragm never sees a difference in pressure across the diaphragm itself so it is never stressed. In theory you don't even need a diaphragm. The sphere would work without one as long as the gas was always trapped above the fluid. You only need the diaphragm to keep the gas in the sphere when it's manufactured and in the box. (OK, OK it may also slow down the diffusion of the gas into the fluid, but I'm making a point here) I concede that if you let the pressure go too low then when you hit a particulary large bump the resultant compression of the gas may cause the diaphragm to hit the top of the sphere and if it has the built in spikes then the diaphragm will be punctured rendering it useless.
No offence intended to anyone. If any of my argument is in doubt, please feel free to humiliate me in public. I have the stocks ready.
cheers
norrie
ps in case you are wondering, I just made the whole lot of this up as I was typing. Never thought of it before. Sorry for the inane ramblings.
The biggest flaw in your argument is basing this on the fact(?) that the membrane is located dead central inside the sphere which I think you'll find is incorrect, therefore, when over 50% or over deflation occurs, the probability of the membrane stretching towards or beyond its elastic limit towards the top of the sphere is not only possible but probable and therefore weakens the structure of the membrane.
Then once recharged, it simply ruptures.
The prospect of having a sphere without the membrane is impossible.
I have a couple of pics here somewhere when I have cut spheres in half; if I can find one I'll post it.
Let's face it mate; if they can design something as ingenious as this type of hydraulic system, they're clever enough to build in little traps that ensure an ongoing sale of spares & done in a manner that mere motals like you 'n me are never going to decipher.[:D][:D]
Alan S [;)]
Then once recharged, it simply ruptures.
The prospect of having a sphere without the membrane is impossible.
I have a couple of pics here somewhere when I have cut spheres in half; if I can find one I'll post it.
Let's face it mate; if they can design something as ingenious as this type of hydraulic system, they're clever enough to build in little traps that ensure an ongoing sale of spares & done in a manner that mere motals like you 'n me are never going to decipher.[:D][:D]
Alan S [;)]
What I can't understand is how the spheres lose gas at all; over the years I have had several BL motors with Hydragas systems, and these seem to retain their nitrogen indefinately, and even when 10 to 15 years old their ride quality is as good as new, and unless there is a hydraulic pipe leak or the system needs depressurising for serious suspension work i.e. knuckle joints need changing, the fluid never seems to need topping up either.
-
tomsheppard
- Posts: 1801
- Joined: 19 Dec 2002, 14:46
- Location: United Kingdom
- My Cars:
The spheres fitted to Citroens are a version of spherical accumulator. This is the form of hydraulic accumulator with the fastest response and greatest resistance to fatigue/wear of the moving part, which in this case is a circular membrane with accordian wrinkles to accommodate excursions from the neutral position with minimal stretching. The button in the centre of the membrane is there to protect it from being extruded through the outlet by nitrogen pressure while there is no hydraulic pressure.
Spherical accumulators are relatively rare in industrial hydraulic systems, because their cost of manufacture for larger volumes is higher, and in my experience as a hydraulic engineer, I have only seen them used industrially when mounted immediately upstream of an axis-cut servovalve.
When used as a gas spring in an automotive suspension, the membrane within the sphere is as dynamic as the wheel's ability to track the road surface, and over the life of a Citroen, the number of cycles of stretch and reversal would be countless millions.
Aging of the membrane would take 2 forms : the loss of plasticising compounds which improve the elasticity of the material, and fatigue. Fatigue is essentially the mechanism of crack propagation, induced by repeated compression and stretching. Crack propagation holds potential for penetrating the membrane until it can no longer withstand the excursions of differential pressure, at whic time a perforation forms, and the gas charge escapes through the circuit to the reservoir.
In the D series spheres, they screw together, and it used to be possible to procure replacement membranes and effectively refurbish the sphere. More recent spheres are clamped and welded around the equator (where the membrane is captured).
Spherical accumulators are relatively rare in industrial hydraulic systems, because their cost of manufacture for larger volumes is higher, and in my experience as a hydraulic engineer, I have only seen them used industrially when mounted immediately upstream of an axis-cut servovalve.
When used as a gas spring in an automotive suspension, the membrane within the sphere is as dynamic as the wheel's ability to track the road surface, and over the life of a Citroen, the number of cycles of stretch and reversal would be countless millions.
Aging of the membrane would take 2 forms : the loss of plasticising compounds which improve the elasticity of the material, and fatigue. Fatigue is essentially the mechanism of crack propagation, induced by repeated compression and stretching. Crack propagation holds potential for penetrating the membrane until it can no longer withstand the excursions of differential pressure, at whic time a perforation forms, and the gas charge escapes through the circuit to the reservoir.
In the D series spheres, they screw together, and it used to be possible to procure replacement membranes and effectively refurbish the sphere. More recent spheres are clamped and welded around the equator (where the membrane is captured).
Alans,
I totally agree with you. Proof of that pudding will come when someone chops one in half to see how far the diaphragm will move before reaching it's unstretched limit. I may even look around my garage to find a really old one and cut it up myself. Time to get the Stihl Saw out I think ! Your automatic assumption of failure during recharge has me puzzled though when you consider the diaphragm situation throughout the process.
Consider the sphere in your hand before you start. The 10 bar left in the sphere presses the diaphragm against the lower half of the sphere in an unstressed state. You remove the plug in the top and the 10 bar reduces to atmospheric. At this point the diaphragm floats because it has atmospheric pressure on both sides - no stress there then. You put the sphere in the charger and start to admit the gas slowly. At the first sign of differential pressure the diaphragm moves to lie aginst the lower half of the sphere. Once at rest in contact with the sphere wall the additional pressure just serves to squeeze the rubber - no different to what it experiences every time you park the car. Once fully charged the plug is tightened and the rubber is squeezed at 70 bar. Once in service, as per my previous hypothesis the pressure on both sides of the diaphragm must rise to say 90 bar to support the weight of the car body. I propose that the diaphragm is under no more stress during recharging than it is during normal service.
The proposal of a sphere without a membrane was a hypothetical one and was not a serious consideration. Can't fault you on the future sales proposition, that makes perfect sense.
bodger
As far as I know the gas permeates through the membrane just as the helium in a baloon passes through the rubber over time. Once it's into the fluid it is carried back to the reservoir and is lost through the vent.
Peter
I agree with 90 % of your theory with the exception of the differential pressure part. In which part of the sphere's normal service life will it experience a differential pressure? Assuming there's no restriction of the diaphragm's movement then the smallest differential pressure will cause the diaphragm to move. As soon as it moves it corrects the differential pressure and the DP returns to zero. The only way for it to experience a DP is to either consider the microseconds it takes to move or Alan's hypothesis that the diaphragm reaches it's non-elastic limit due to insufficient gas pressure and an assymetric diaphragm. Not sure I agree with the 'accordion wrinkles' but Alan's cut away should answer that one.
mmmmm... I like a good debate
Cheers
noz
I totally agree with you. Proof of that pudding will come when someone chops one in half to see how far the diaphragm will move before reaching it's unstretched limit. I may even look around my garage to find a really old one and cut it up myself. Time to get the Stihl Saw out I think ! Your automatic assumption of failure during recharge has me puzzled though when you consider the diaphragm situation throughout the process.
Consider the sphere in your hand before you start. The 10 bar left in the sphere presses the diaphragm against the lower half of the sphere in an unstressed state. You remove the plug in the top and the 10 bar reduces to atmospheric. At this point the diaphragm floats because it has atmospheric pressure on both sides - no stress there then. You put the sphere in the charger and start to admit the gas slowly. At the first sign of differential pressure the diaphragm moves to lie aginst the lower half of the sphere. Once at rest in contact with the sphere wall the additional pressure just serves to squeeze the rubber - no different to what it experiences every time you park the car. Once fully charged the plug is tightened and the rubber is squeezed at 70 bar. Once in service, as per my previous hypothesis the pressure on both sides of the diaphragm must rise to say 90 bar to support the weight of the car body. I propose that the diaphragm is under no more stress during recharging than it is during normal service.
The proposal of a sphere without a membrane was a hypothetical one and was not a serious consideration. Can't fault you on the future sales proposition, that makes perfect sense.
bodger
As far as I know the gas permeates through the membrane just as the helium in a baloon passes through the rubber over time. Once it's into the fluid it is carried back to the reservoir and is lost through the vent.
Peter
I agree with 90 % of your theory with the exception of the differential pressure part. In which part of the sphere's normal service life will it experience a differential pressure? Assuming there's no restriction of the diaphragm's movement then the smallest differential pressure will cause the diaphragm to move. As soon as it moves it corrects the differential pressure and the DP returns to zero. The only way for it to experience a DP is to either consider the microseconds it takes to move or Alan's hypothesis that the diaphragm reaches it's non-elastic limit due to insufficient gas pressure and an assymetric diaphragm. Not sure I agree with the 'accordion wrinkles' but Alan's cut away should answer that one.
mmmmm... I like a good debate
Cheers
noz
Anyone remembers the Central heating system's expansion chambers ?
In old days this was a simple reservoir with an opening to free air - found on the highest point in the system - i.e. close under the roof.
These days a closed expansion chamber is used - located next to the boiler.
Either a large ball - or a flat circular tank - some 20"-25" in dia.
Inside the expansion chamber you have a rubber membrane - dividing the chamber into 2 individual cavities.
- so has the Citroen sphere.
One cavity inside the expansion chamber would be pre-charged thru a standard tyre valve (usually some 1.5bar).
The other cavity receives/delivers water according to the central heating system temp - and thus the volume of water at given temp.
If water side disconnected - and water allowed to escape - the precharge would press out every drop of water from the water cavity.
- so is the Citroen sphere functioning :
One cavity is precharged with Nitrogen - thru an orifice blocked by a plug & seal during production/charging (a valve can be fitted).
The other cavity receives/delivers the hydraulic fluid - through an orifice within the threaded end - according to the pressure of the fluid - due to a suspension cylinder compressed by vehicle weight - or the same cylinder allowed to expand - if the associated wheel hits a pothole.
If hydraulic fluid side disconnected - the precharge would press out every drop of hydraulic fluid from this cavity.
For both - the same problem arises after a given time :
The expansion chamber needs a regular check of the precharge pressure - and a standard tyre pump is used to top up the pressure.
This is because of dispersion of air thru the membrane to the water - and/or leaks from the valve.
If the chamber is not regularly checked/pumped - you get the problem of a noisy central heating system - as the air cavity may be completely compressed/lost for long - making the membrane more or less "vulcanise" itself to the inner wall of the empty cavity.
This is when you need to frequently top up the water on the system - and air is noising around in the pipes/radiators.
I think quite a few real estate owners have tried call the blacksmith curing such problems - often involving the expansion chamber replaced.
- the same thing happens to the Citroen sphere.
Instead of the noise - you're alarmed by the rather un-comfortable ride.
Same principle -
Different usage -
Different symptoms on failure -
(BTW : Anders - what is a central heating system ?? - and what is an expansion chamber ??)
In old days this was a simple reservoir with an opening to free air - found on the highest point in the system - i.e. close under the roof.
These days a closed expansion chamber is used - located next to the boiler.
Either a large ball - or a flat circular tank - some 20"-25" in dia.
Inside the expansion chamber you have a rubber membrane - dividing the chamber into 2 individual cavities.
- so has the Citroen sphere.
One cavity inside the expansion chamber would be pre-charged thru a standard tyre valve (usually some 1.5bar).
The other cavity receives/delivers water according to the central heating system temp - and thus the volume of water at given temp.
If water side disconnected - and water allowed to escape - the precharge would press out every drop of water from the water cavity.
- so is the Citroen sphere functioning :
One cavity is precharged with Nitrogen - thru an orifice blocked by a plug & seal during production/charging (a valve can be fitted).
The other cavity receives/delivers the hydraulic fluid - through an orifice within the threaded end - according to the pressure of the fluid - due to a suspension cylinder compressed by vehicle weight - or the same cylinder allowed to expand - if the associated wheel hits a pothole.
If hydraulic fluid side disconnected - the precharge would press out every drop of hydraulic fluid from this cavity.
For both - the same problem arises after a given time :
The expansion chamber needs a regular check of the precharge pressure - and a standard tyre pump is used to top up the pressure.
This is because of dispersion of air thru the membrane to the water - and/or leaks from the valve.
If the chamber is not regularly checked/pumped - you get the problem of a noisy central heating system - as the air cavity may be completely compressed/lost for long - making the membrane more or less "vulcanise" itself to the inner wall of the empty cavity.
This is when you need to frequently top up the water on the system - and air is noising around in the pipes/radiators.
I think quite a few real estate owners have tried call the blacksmith curing such problems - often involving the expansion chamber replaced.
- the same thing happens to the Citroen sphere.
Instead of the noise - you're alarmed by the rather un-comfortable ride.
Same principle -
Different usage -
Different symptoms on failure -
(BTW : Anders - what is a central heating system ?? - and what is an expansion chamber ??)
If you look at the little "action photo" I posted, I think it is really self explanatory; look at where & how the mebrane is attached & the shape it takes as well as how far the edge flexes when the LHM is in there.
Now what happens when the N2 is missing? How far does it go into the upper part of the chamber & at what angle is the mounted part of the mebrane forced?
The answer is in that sketch.
Alan S
Now what happens when the N2 is missing? How far does it go into the upper part of the chamber & at what angle is the mounted part of the mebrane forced?
The answer is in that sketch.
Alan S
I got the answer I was really looking for to the same question posted on XM-L, Yahoo. I hope this will save 2 spheres which would otherwise have gone in the bin. Here's Vince's reply:
The clamp plate is inside the bladder and seals it against the sphere shell
when you tighten the nut. The bladder has a rib around the opening which is
gripped by the clamp plate. Have a look at the sphere cross section on the
internet or in the manual may be a picture.
The bladder is like a ballon with an opening on the top. I guess 50MM
diameter with a rib around the inner rim.
Ths clamp plate is designed to grip the inner rib and seal it when you
tighten the plug.
You need a bolt with a 7mm thread to match the plug thread. Length is not
important as long as you do not push it in a unscrew it without pulling the
plate back firmly. Play safe and do it upside down. Replace the plug and
regass and tighten. What probably happens is when youi release the plug the
bladder slips out of alignment with the clamp plate and you are partially
clamping the rib which allows gas to escape.
Hope this explains it slightly better.
regards
vince
----- Original Message -----
From: "Norrie" <norrie@h...>
To: <CX-L@yahoogroups.com>
Sent: Wednesday, March 10, 2004 8:41 AM
Subject: [CX-L] Re: Sphere regassing troubles
Vince,
Now you sound like a man who knows what they're talking about.
I have quite a bit of experience with spheres and as such just cannot
believe that two perfectly OK spheres can exhibit such a degree of
leakage without a simple explanation and that explanation does NOT
include burst diaphragms !
Can you just run me through those steps again? A picture would be
worth a thousand words.
Where is the clamp plate, what's its purpose and how/why does it
seal/not seal? What shape is it? I pictured only one sealing surface
on the diaphragm, around the perimeter edge.
A long bolt? diameter/length? inserted from which end? plug end
presumably?
What are you feeling for with the bolt? do you need to waggle it
from side to side/up and down? How do you know you've been
sucessful? Do I need to apply pressure from the valve end to seat
the diaphragm?
I think the existing plug is M8 or thereabouts. Is it a longer M8 I
need or something which passes easily through the threaded part. If
so, what am I trying to locate with once passing through the
threaded part?
More information would be invaluable. It may stop 2 perfectly good
spheres going in the bin.
Many thanks
Norrie
--- In CX-L@yahoogroups.com, "Vince Baker" <engmepho@o...> wrote:
> Hi
> Possible the bladder has not sealed against the clamp plate
correctly. I use
> a long bolt and push the clamp plate in first then pull it back to
reseat
> it. This allows the clamp plate to seal properly. Try it on some
faulty
> spheres and see what happens.
> Regards
> Vince
The clamp plate is inside the bladder and seals it against the sphere shell
when you tighten the nut. The bladder has a rib around the opening which is
gripped by the clamp plate. Have a look at the sphere cross section on the
internet or in the manual may be a picture.
The bladder is like a ballon with an opening on the top. I guess 50MM
diameter with a rib around the inner rim.
Ths clamp plate is designed to grip the inner rib and seal it when you
tighten the plug.
You need a bolt with a 7mm thread to match the plug thread. Length is not
important as long as you do not push it in a unscrew it without pulling the
plate back firmly. Play safe and do it upside down. Replace the plug and
regass and tighten. What probably happens is when youi release the plug the
bladder slips out of alignment with the clamp plate and you are partially
clamping the rib which allows gas to escape.
Hope this explains it slightly better.
regards
vince
----- Original Message -----
From: "Norrie" <norrie@h...>
To: <CX-L@yahoogroups.com>
Sent: Wednesday, March 10, 2004 8:41 AM
Subject: [CX-L] Re: Sphere regassing troubles
Vince,
Now you sound like a man who knows what they're talking about.
I have quite a bit of experience with spheres and as such just cannot
believe that two perfectly OK spheres can exhibit such a degree of
leakage without a simple explanation and that explanation does NOT
include burst diaphragms !
Can you just run me through those steps again? A picture would be
worth a thousand words.
Where is the clamp plate, what's its purpose and how/why does it
seal/not seal? What shape is it? I pictured only one sealing surface
on the diaphragm, around the perimeter edge.
A long bolt? diameter/length? inserted from which end? plug end
presumably?
What are you feeling for with the bolt? do you need to waggle it
from side to side/up and down? How do you know you've been
sucessful? Do I need to apply pressure from the valve end to seat
the diaphragm?
I think the existing plug is M8 or thereabouts. Is it a longer M8 I
need or something which passes easily through the threaded part. If
so, what am I trying to locate with once passing through the
threaded part?
More information would be invaluable. It may stop 2 perfectly good
spheres going in the bin.
Many thanks
Norrie
--- In CX-L@yahoogroups.com, "Vince Baker" <engmepho@o...> wrote:
> Hi
> Possible the bladder has not sealed against the clamp plate
correctly. I use
> a long bolt and push the clamp plate in first then pull it back to
reseat
> it. This allows the clamp plate to seal properly. Try it on some
faulty
> spheres and see what happens.
> Regards
> Vince
-
Kowalski
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<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by alans</i>
If you look at the little "action photo" I posted, I think it is really self explanatory; look at where & how the mebrane is attached & the shape it takes as well as how far the edge flexes when the LHM is in there.
Now what happens when the N2 is missing? How far does it go into the upper part of the chamber & at what angle is the mounted part of the mebrane forced?
The answer is in that sketch.
Alan S
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
The sketch is inaccurate. The membrane is not actually flat but is more like a baloon with a larger volume than the sphere, therefore, it can be either completely filled with gas or LHM without having to stretch.
There is a picture of a cross section of a sphere on the ALKO spheres box if you want to have a look...
If you look at the little "action photo" I posted, I think it is really self explanatory; look at where & how the mebrane is attached & the shape it takes as well as how far the edge flexes when the LHM is in there.
Now what happens when the N2 is missing? How far does it go into the upper part of the chamber & at what angle is the mounted part of the mebrane forced?
The answer is in that sketch.
Alan S
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
The sketch is inaccurate. The membrane is not actually flat but is more like a baloon with a larger volume than the sphere, therefore, it can be either completely filled with gas or LHM without having to stretch.
There is a picture of a cross section of a sphere on the ALKO spheres box if you want to have a look...