Guessing:

- Hydraulic chamber geometry (I believe the front has smaller volume)
- N2 sphere geometry (but I think they are the same)
- Factory N2 pressure

In NZ some people have used front spheres with rear displacers. Due to the scarcity of serviceable replacement units. Not recommended, but may work.

BTW. If you have servicable spheres with intact hydraulics, you can have them regassed in NZ. The cost is minimal, and truly restores factory ride and handling. But getting spheres to and from will probably be a challenge.

 

Placing a front and rear sphere next to one another, the outside dimensions are almost identical.


I've heard of front spheres being used on the rear, just swapping the cones, and that the ride and handling is almost identical, if not the same. That's what has made me wonder if there is a difference in the internal valve or not.


I've actually just finished repressurizing two rear sphere this past weekend and am about to set about having a couple rear sphere's repressurized as well.

 

Yup, mowog, i go with the theory that if one uses the rear mechanical linkages, ( which are different from the front ) and re gasses the top sphere, then its possible to swap front to rear...

it is the spec of the damper valve in the middle that is in question, since the rear has more weight to support than the front, and in theory must operate at a different rate or pressure..? ie its configured to do a different thing . the gas and hydraulic pressure are the same.. but the way the damper valve works should be different... else with the extra weight on a front damper valve put in a rear position, its seeing pressure it didnt see, when it was on the front..?

so its going to open and close different? the extra weight is going to compress the gas more.. the damper valve will see that. in effect the front damper valve put in a rear position, becomes preloaded.

i dont know if the spec on the damper valve between front and rear is different... but i do see a different action.. and if mgf could have used the same part front and rear.. only needing to change the bottom piston link... then it would have been cheaper and more cost efficient... but they didnt... and i think there is a difference in that damper valve..


maybe that isnt so.. i cant find any specific info yet...

Quote : "The Hydragas fluid in the upper sphere communicates with the lower sphere via a 'damper valve' that controls the rate at which the fluid can enter or exit the upper sphere, and thus has a critical impact upon both springing and damping."

Hydragas

for me the real cure would be to make that damper valve external, and therefore serviceable. but thats probably not something i will try while regassing cures the fault..

if one takes a unit to bits... one can see the damper..MGF rear hydragas unit from inside

looking at dieters excellent pics and explanation, i suspect the front damper valve may have different spring tensions and hole diameters. but until one does what dieter did, and compares the two... i cant say...

the first part of this forum discussion explains what going on in a dual acting shock absorber.. using hydraulic oil and gas... in effect its a very similar action to the hydragas.. http://www.f1technical.net/forum/viewtopic.php?t=8937&start=195
the difference being the damper valve doesnt move in the hydragas - its fixed. The hydragas uses two flexible seals instead, one for the piston rod and one for the gas seal, with the damper valve fixed in between... it also means one cant adjust the rates of that sealed in damper valve... so if there is any difference between the front and back damper valve, one cant change it.

 

I agree, the damper valve in a rear unit must be different that in a front unit and so the two are not truly interchangeable for one another even if the displacement cones are swapped. But others have swapped front for rear with acceptable results I have been told.

At the moment, I have 5 rears and 3 front spare spheres and I have taken two of the front’s and modified them with Schrader valves and have recharged them to 16.55bar. I’m looking to modify a couple rears in the next couple of weeks. :smile:

 

i wonder about using a different compressible gas, than nitrogen, mowog.

i think about argon.. because its heavier than air. CO2 is not a choice because of its reaction with hydrogen and oxygen, but i think about argon because of its ability to be non reactive, and being heavier than air.

using it, would mean it would displace air... being heavier, and so air in the chamber would naturally sit at the top, like oil floats on water,

that would mean given settle time... one could bleed off air content in the chamber, because its closest to the valve one puts in, and so over time one would have an argon filled chamber... without, any other gas...



so.. one inhibits rust and reaction , by excluding things which begin it?

that said i dont know - this mo as i post, how the compression of argon is dissimilar to nitrogen. if the change is big... one would have to weigh up the differences the damper valve would see.

i just like the idea of argon this mo, because of it non reactivity, and being heavier than air... being heavier, it wants to stay below air... than above it.. even under pressure..?

so lets suppose one fills a hot dry chamber with argon. any air will naturally not mix or react with it... and it displaces air over time.. naturally sitting in the lowest point.. which is the gas gasket...

if it leaks, through the gasket or the valve, or even the steel chamber, or a weld - maybe its detectable? are there argon sensors one could use to detect a leak.?

unlike nitrogen.. argon will naturally seek the lowest point... because it is heavier than the air its leaking into.

" argon is about 1 1/2 times heavier than air so will fill confined spaces from the bottom up"

i think that has benefit, this mo.

 

Could you put up some pictures of the modified spheres when you're finished please.

 

> I've actually just finished repressurizing two rear sphere this past weekend

Ditto for the request for pics (and a how to guide if you did anything different from the other suggested options - particularly if you didn't weld it in!).

Re using argon, I'd considered this, and would probably take a similar approach to when carbonating my home brew. Put pure gas in to say 30 psi (theren diluting the air), let gas out. Mor More pure gas in to 30psi, and let it out. I figure after 4 or 5 times, there's not going to be much gas other than argon in there. I figure only 30% other gases should be left after each attempt. So 30%, 10%, 3%, 1%, less than 1%.

 

"
argon is a monatomic gas (i.e. consists of single atoms) and nitrogen is a diatomic gas (molecules contain two atoms), which would make nitrogen molecules physically much bigger. An argon atom has a relative mass of 40, a nitrogen molecule has a relative mass of 28. I suspect that he difference in mass is far less significant than the difference in physical size, as far as leaking out is concerned."


its the non reaction of argon, unlike nitrogen that is of benefit... nitrogen can produce oxides..

because argon is heavier than air might have some purging benefit, but it is four times the cost of nitrogen...

Because it's heavier, it means it naturally wants to sit in the "bottom" of the gas chamber in relation to the schrader valve at the top.. and this might protect the damper valve from corrosion better... since if it leaks through the diaphragm, thats where it will go. but those dampers are getting old now... its likely that all of them are not working like they were designed to.

"
Nitrogen is about 3% lighter than air. It diffuses rapidly with air and won't stay in an open top container. Nitrogen will not displace air. *** Argon is about 38% heavier than air. It diffuses more slowly in air than nitrogen does. It will stay in an open top container much longer than nitrogen. Argon will displace air."


getting that damper valve outside the two chambers would make it much easier to service, then it wouldn't matter really if one used nitrogen or argon...

being a welding shield gas, argon is easily bought over the counter... but its purity might be in question.

 

if one is interested in an in depth topic, about diaphragm based shock absorbance, this company make a similar "hydragas" shock absorber.

http://qhp.co.uk/cms/uploads/HydraulicDampers.pdf

 

this is an interesting idea...

https://www.hydac.com/de-en/products/hydraulic-accumulators/diaphragm-accumulators.html


https://www.hydac.com/fileadmin/pdb/pdf/PRO0000000000000000000003100270011.pdf

one could replace the top chamber with one of these and use an external damper valve as its link to the hydraulic chamber?

its interesting enough for me to ask hydac what they think..

not going to be a cheap solution... i think.. but its as close to a new hydragas system ive seen. new components... serviceable from top to bottom... thats got to be worth investigating to keep mgf`s on the road.

 

I am actually using argon welding gas because of the convenience. The gas is 75% argon, 25% nitrogen.
I will post a couple pictures of the spheres. I’m really building on the work of Tim Guy. His thread on modifying sphere from 2015 (I think) is full of excellent information and drawings.
I’ve using schrader valves that are rated for 800 psig (55.15 bar), which also happens to be the max working pressure of the sphere (stamped on the top of the sphere). The welding of the threaded bung to the sphere is being done by a friend who is a boiler maker by trade. He’s tig welding the bung to the sphere and the first two look beautiful and are holding pressure. This week or next I am hoping to get him a couple rear spheres.

 

Here's a picture of the modified sphere.

 

Awesome! How did you weld the sphere? Mig? Can't quite make it out in the background.

Re argon vs nitrogen, I had also initially considered that N2 would be physically larger than Argon, however the boiling points are similar, indeed Argon has a higher boiling point than nitrogen. This would suggest Argon is of a similar, if not larger physical size than nitrogen. If so, leakage should not be any more of an issue than that with Nitrogen filled spheres.

 

Doh, sorry, just read you'd said it was TIG welded in your post above! Just remember the rears need to be offset!

 

I initially tried to weld a bung on using my MIG welder that you see in the picture, but I couldn't get an air tight weld, so I took it to a friend that is a welder by trade and he TIG welded the bung on. I figured if he can weld pipes at a refinery, he can weld a bung on in his sleep.


My MIG welder is in the picture because of the welding gas bottle that I am accessing at the back of the welder.


After 4 days, both spheres still have 250 psig (17.2 bar) of pressurised argon in them. Now its time to have a couple rear spheres modified.


I'll be using the excellent drawings that Tim Guy produced for positioning the threaded bung on the rear, both of which are different.