Topic

I am going to regas my Hydragas spheres as they are 25 years old and I expect that they will be pretty shot as the ride isn't wonderful (although it isn't quite bad). I need to know a couple of things before I do this which I cannot find in the usual how to guides, so I'm after a bit of help, please/
I need to know the thickness of the sphere where it is drilled, which will allow me to determine whether my mig brazing skills are adequate to do the job myself and I would like to know where suitable weld bungs can be sourced. I know that I can buy stuff reconditioned or have the job done for about half of what the car is worth but for me most of the fun of owning an old car is in using ingeniuity and my own tools. Is anybody able to point me in the right direction, please?

Further reading brings up the answers. There is enough metal to drill and tap the sphere casing, screw in a valve and soft solder it in place over solder paste. Bingo. Eight quid for the valves (brass cased onse so they solder easily,) Tap, Think I've got one at Work, if not £10. Just need the filler connector and a bottle of nitrogen. I have Argon and a regulator so I reckon I'm in. Might try doing this in situ. Seens possible to me,

I've cut one in half, I'll see if I can find it and take a pic. Wait a few days, and I'll get around to it

Thank you Cobber. I strongly suspect it might be even easier. Loctite 638 on the threads of the valve will work at this pressure. Calculating the maximum pressure on the inserted valve to be under 25 lbs at the sphere maximum of 800 psi, it seems feasible to drop the fluid pressure to near zero for the sake of the diaphragm, raise the wheels off the ground, drill, tap, loctite valve in and pressurise each sphere before pumping up to trim height. No heat required. Have the tap as well and the 21/64" drill bit so hopefully the plan will come together. Valves on order.

It is interesting as no one has tried this before or maybe they have and not posted the result, I know that Mike Satur sells the shrader valve with a compressible collar so you only need to drill the hole and insert the valve and tighten with a spanner, and then fill with Nitrogen, that may be easier than tapping and relying on a very thin threaded hole even with loctite.

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That is certainly something to consider. My company uses lots of these fittings. Many of them leak. I am sceptical about them, especially on a domed surface. I need about 75 thou thickness to ensure two full turns which ought to be enough. Just under 2 mm. Failing that I would need to solder with Fryolux flux and a flame.
There are loctites and loctites, of course. 638 is a tough one.

No I'm not doubting your methods just curiosity as why no one has posted about success with this method before, I had mine replaced by Dawn and Ian Kennedy I am technically capable of doing it myself but jobs like this can be physically challenging to me now so let the well versed do the job for me, they fit the refurbed type with welded collets and schrader valves, I have to say they both worked extremely hard for the money for two hours but the ride quality now is superb. Good luck with whatever method you choose, please report back with results it makes interesting reading.

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Dutch enthusiasts solder the valves in using soft solder. Loctite seals the thread more easily and will retain the valve much better. Provided enough wall thickness exists this will work as long as the threads can withstand the force exerted upon them which is actually very small. The maximum pressure the sphere can withstand is 800 psi 54 bar. The size of the valve is .0845 of a square inch. Worst case pressure upon it will be 68 pounds. Can you hang 68 pounds from the valve once installed? If you can, it works . I expect it will. A 68 pound pull on a valve screwed into a similar thickness of steel will prove the working before drilling the sphere

Got it 2mm. That will allow two and a bit full threads. Doable, not least because the metal around the thread is domed so the can is strong enough not to distort

I am a hydraulic engineer working on systems up to 500bar, and air systems to 50 bar.

I would not attemp to repair in the way you are planning.

I would never use a brass fitting for anything over 15bar. Its shear strength is just not high enough.

Tapping into metal that is so thin is also very poor practice, and again risks shearing.

You talk of 50bar as being the pressure in the sphere, but that is the static pressure. During "spring" compression the volume could easily be halfed as the strut rises and compresses the nitrogen. Using the gas equations (boyles law), that would double the pressure in the spher. Compress it further, and you could be on the way to 150-200 bar for a moment.

Now I deal with industrial applications, and at higher pressures, and more critical applications, so everything suggested is possible, but do not understimate the potential for disaster when dealing with gas pressures as high as 50bar or more. Volumes are small (lower stored energy), but still enough to turn a small fitting into a high velocity projectile that can blow your head off!

Just take extreme care whatever you do

Thank you for that. The static pressure is 15 but I heed your caution regarding shear strength. I have suitable test facilities and the experience to use them correctly but would prefer to carry out full pressure tests on the car in its proper environment because I want to find a way of doing this without major dismantling in order to save as many cars as possible. I have not found the Mike Satur parts referred to so I assume that they are not available. I have reservations about using blind nuts in this application anyway.

Before you drill or do anything I suggest you apply a vacuum to the fluid port, to draw the diaphragm down outta harms way