Re-gassing spheres to a lower pressure?

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Kyleb
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Re-gassing spheres to a lower pressure?

Post by Kyleb » Tue Sep 19, 2017 9:15 pm

Can I re-gas my spheres to a lower pressure? If so where's the best place to go to get custom pressures?

Thanks

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Re: Re-gassing spheres to a lower pressure?

Post by Defender110 » Wed Sep 20, 2017 1:23 pm

Why would you want to?
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Re: Re-gassing spheres to a lower pressure?

Post by Kyleb » Wed Sep 20, 2017 1:51 pm

Defender110 wrote:
Wed Sep 20, 2017 1:23 pm
Why would you want to?


I'm running a custom hydraulic suspension setup on my Volkswagen Beetle and it's way to stiff at the moment!

I was hoping that I'd be able to get some info about how I'd go about softening then on here :)

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Re: Re-gassing spheres to a lower pressure?

Post by jamescarruthers » Wed Sep 20, 2017 3:10 pm

Remember it depends upon hole size and pressure
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Re: Re-gassing spheres to a lower pressure?

Post by Defender110 » Wed Sep 20, 2017 3:50 pm

As James has said , bigger hole size allowing quicker/more fluid movement. Sphere shop may be able to help or Westeroen in Stockport

http://www.sphere-shop.co.uk/
http://www.westroen-spheres.co.uk/
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Re: Re-gassing spheres to a lower pressure?

Post by jamescarruthers » Wed Sep 20, 2017 6:21 pm

I think Martin at Pleiades has done a few customs I think.
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Re: Re-gassing spheres to a lower pressure?

Post by jamescarruthers » Wed Sep 20, 2017 6:34 pm

I have heard that you can do a quick weld of the damper hole then drill it back to the size you want
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Re: Re-gassing spheres to a lower pressure?

Post by Kyleb » Wed Sep 20, 2017 7:38 pm

Thanks for the input guys! I'm running accumulator spheres so no damper? Meaning the hole is wide open right?

I think the problem lies in the fact I probably only have around 150psi oil pressure!

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Re: Re-gassing spheres to a lower pressure?

Post by jamescarruthers » Wed Sep 20, 2017 8:01 pm

You need a regular sphere (damped) at each strut and an accumulator in line for reserve pressure/dampen things out
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Re: Re-gassing spheres to a lower pressure?

Post by xantia_v6 » Wed Sep 20, 2017 8:34 pm

I think that 150 PSI is much lower than any Citroen suspension, the hydraulic pressure is normally higher than the sphere pressure, so that the diaphragm is partly compressed under static conditions.

Your sphere diaphragms might not be moving at all because the spheres may (depending on model) have 750 PSI in them. You may have some trouble getting the damping right at your pressure range (even after lowering the sphere pressure).

You can learn something about Citroen spheres with damping elements in the FCF topic:
https://frenchcarforum.co.uk/forum/view ... =3&t=55077 (particularly the pictures near the bottom of page 2).

Remember also that when the sphere is in is normal operating range, a higher sphere pressure gives softer suspension, and a lower sphere pressure gives harder suspension.

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Re: Re-gassing spheres to a lower pressure?

Post by Kyleb » Wed Sep 20, 2017 8:54 pm

xantia_v6 wrote:
Wed Sep 20, 2017 8:34 pm
I think that 150 PSI is much lower than any Citroen suspension, the hydraulic pressure is normally higher than the sphere pressure, so that the diaphragm is partly compressed under static conditions.

Your sphere diaphragms might not be moving at all because the spheres may (depending on model) have 750 PSI in them. You may have some trouble getting the damping right at your pressure range (even after lowering the sphere pressure).

You can learn something about Citroen spheres with damping elements in the FCF topic:
https://frenchcarforum.co.uk/forum/view ... =3&t=55077 (particularly the pictures near the bottom of page 2).

Remember also that when the sphere is in is normal operating range, a higher sphere pressure gives softer suspension, and a lower sphere pressure gives harder suspension.


Am I right in thinking I should try to equal out the pressures on either side of the diaphragm and start from there?

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Re: Re-gassing spheres to a lower pressure?

Post by xantia_v6 » Wed Sep 20, 2017 9:15 pm

The Citroen systems usually run with the hydraulic pressure higher than the (unloaded) sphere gas pressure, so that suspension compression reducing the volume of gas gives an increasing spring rate. The volume of oil moved by your struts should be taken into account. I guess with the suspension fully compressed, you want the gas volume in the sphere to be about 20% of the sphere total volume, if you know what spring rate you want, you can estimate the hydraulic pressure under those conditions, then using Boyles law, calculate the sphere pressure with no hydraulic pressure...

Other formuli are available....

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Re: Re-gassing spheres to a lower pressure?

Post by Kyleb » Wed Sep 20, 2017 9:22 pm

xantia_v6 wrote:
Wed Sep 20, 2017 9:15 pm
The Citroen systems usually run with the hydraulic pressure higher than the (unloaded) sphere gas pressure, so that suspension compression reducing the volume of gas gives an increasing spring rate. The volume of oil moved by your struts should be taken into account. I guess with the suspension fully compressed, you want the gas volume in the sphere to be about 20% of the sphere total volume, if you know what spring rate you want, you can estimate the hydraulic pressure under those conditions, then using Boyles law, calculate the sphere pressure with no hydraulic pressure...

Other formuli are available....


This sounds promising! I'd like just a stock spring rate! I guess soft for bx! Haha.

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Re: Re-gassing spheres to a lower pressure?

Post by senmathal » Wed Sep 20, 2017 10:35 pm

This i complicated to understand even if you have worked on a Citroen garage.

But usually the suspension get stiffer when loosing pressure in the sphere, not softer, and the suspension way will be shorter. The oil pressure in the strut is not the same as it is in the system. As oil is not compressible you can compare the oil in the strut as a steel leg. With the oil you adjust the length of the strut and the height of the car. Not the suspension stiffness. The only thing that happen if you increase the pressure of the oil is that the car get higher up. But close to the top level the suspension get stiffer and in the top is no suspension at all. If you have enough pressure to lift the car in to the right level you don´t have use of any higher pressure. In normal driving position it is the wight of the car that compressing the gas.

/Mats

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Re: Re-gassing spheres to a lower pressure?

Post by Kyleb » Thu Sep 21, 2017 9:13 am

senmathal wrote:
Wed Sep 20, 2017 10:35 pm
This i complicated to understand even if you have worked on a Citroen garage.

But usually the suspension get stiffer when loosing pressure in the sphere, not softer, and the suspension way will be shorter. The oil pressure in the strut is not the same as it is in the system. As oil is not compressible you can compare the oil in the strut as a steel leg. With the oil you adjust the length of the strut and the height of the car. Not the suspension stiffness. The only thing that happen if you increase the pressure of the oil is that the car get higher up. But close to the top level the suspension get stiffer and in the top is no suspension at all. If you have enough pressure to lift the car in to the right level you don´t have use of any higher pressure. In normal driving position it is the wight of the car that compressing the gas.

/Mats


Yeah that's exactly how my system works, but the only pressure in the whole system is just the weight of the car, I have a electric pump the only kicks in when I alter the height.

The spheres are brand new so they won't be flat, also my cars much lighter than the Citroen they spheres are made for I would thought?