Sphere specs

[Mandrake]

As promised, I did get to work on an XM-type sphere, to extract and examine the leaf-valve...

Excellent work Chris! This thread and these pictures really need to be preserved somehow, I don't think I've seen any photos online of a dismembered damper valve from a post-DS sphere before...apparently nobody has taken the trouble to dismember and photograph one before.

^ Central damper drilling, seemingly marked 32 (not 2 and E, as I thought before), and marked with what appears to be a manually applied centrepunch. Very odd. Note the countersinking for the drilling, added to later spheres, to improve fluid flow.

Is it a Hydractive 2 strut sphere by any chance ? That central drilling looks really small - 0.7mm ?

The numbers are unlikely to be manually centre punched... more likely it was done by a robot.

^ Leaf washer positioning, with apologies for the mixed units. Interesting to note that the individual washers have extremely tiny amounts of flex.

Yep they are very stiff indeed, they are a high grade of spring steel, designed to flex back and forth without losing their tension for years. (Since a loss of tension would cause a reduction in damping)

Interesting the difference in damping between the two sides, the washers controlling the "in" flow to the sphere are thinner (2x7 + 9 versus 2x9 +7) and also have one that is a smaller diameter ? This difference is consistent with a Hydractive strut sphere where the damping rates for in are softer than out. (If you cut open a standard sphere you should find both sides have the same stack of washers)

It's not immediately clear to me what effect having a smaller diameter washer on the top of the stack instead of all the same diameter would have - perhaps this provides some degree of progressive damping where the valve opens easier initially but once the bottom two washers on the top side of the valve bend a certain amount the third washer starts to exert its influence by stiffening up the valve for further opening ??

I also have no idea what the difference in colour between the different washers might be for - perhaps it signifies a different grade of steel with different springyness ? (But why bother, when you could just get the degree of stiffness you want from the total stack thickness of a uniform grade of material ?)

Its interesting to note that the DS workshop manual showed a diagram of the damper valve and washers almost exactly like yours complete with thicknesses as part of the service data - since the damper valves on those were serviceable. It listed the different washer combinations for different models of DS!

^^ Outer and inner views of the damper body. Large central drilling for the central sleeve is 7mm diameter, and all other holes are 4mm, parallel sided. Note the raised and machined surface for every alternate hole; on this surface seats the leaf washer. This provides two one-way and pressure-sensitive valves, one in and one out.

It's good to know I wasn't too far off the correct figures of 8x 4mm holes. I have seen a cut open valve before but its a long time ago. That's 50.3 mm^2 hole area in each direction, compared to 0.49mm^2 hole area for the bypass hole, assuming the bypass hole is 0.7mm. It should be clear from that that anything but the smallest gentlest movement cannot pass through the centre hole, it's just far too restricting.

^ Side views showing raised seats, and clearance between the flex-washer and the lower set of holes.

That casting for the middle of the damper is a bit different to the CX sphere I've seen cut apart, which was more like a flat with depressions for the inlets rather than flat for the inlets and raised edges for the returns, but its functionally the same.

This is a part I haven't dismembered before, and it has provided quite an insight into a component which is crucial to the Citroen ride.

What I like is the extreme simplicity and elegance of this damper valve design, and always have done. Because you already have a hydraulic ram linked to the suspension movement the only thing you have to add for damping is that tiny little valve - which replaces the entire shock absorber on conventional suspension... And yet you could argue that it works better.

[white exec]

Simon,

Thanks for the further interpretation.
The sphere was H2 - an XM rear - 400/30/0.7 - although I measured the central drilling carefully, and got 0.6mm.

Not sure about the small (top) inner washer. It is spring steel, like the other bright ones, and could be there to provide some cushioning from the substantial peen on top of it. More likely, though, I think, is what you say: that damping in is designed to less than damping out.

Actual diameters are:
Large washers: 21mm
1mm spacer: 10mm
Innermost small washer: 14mm

On HA2 XM, the only real softness of ride to be had (particularly at the lightly loaded back end) is from the centre HA sphere. If this is inoperative (flat, or faulty electrovalve), the back end ride is extremely harsh. Bounce test in 'firm' makes you wonder whether there's any springing there at all. However, when driving through fast curves and things flip to 'firm', the whole car is extremely well composed and controlled.

One other detail I missed refers to the central drilling. My schematic suggests that the (0.7mm) narrow bore runs the whole length of the central spigot: it doesn't. The 0.7mm drilling only occupies the outermost end of the spigot, where it is about 1mm or less in length, and countersunk at both ends. The rest of the central drilling is just over 3.5mm diameter. The damping to LHM is considerable, but less than a lengthy tiny drilling would present.

It's also easy, I think, to overestimate the total size of the damping apertures opened up when the leaf valve opens, in response to shock. Although the bleed-off holes are 4 x 4mm diam (massive), the leaves themselves, being stiff, will only open 'a tad' - heaven knows by exactly how much (and I'm not about to set about discovering!).

So the ratio of damping 'closed:open' is anyone's guess. I would be surprised if Citroen ever established this empirically, but having thought out the principle of the damper valve, simply road tested various concoctions until they got it right. As you say, they did have a bit of history to work with.

Re: washer flex, if you wanted a comparison, I'd say that the flexibility of a single large washer was about the same as that of a Swann-Morton scalpel blade, although the washers might be only half as thick; pretty stiff.

[spider]

Quite a lot (if not nearly all to be completely honest) of the information in this topic is beyond me at the moment however it has been a fascinating read in honesty to learn more.

[Xantippa]

Any info about C5 X7 sphere specs, eg. damper hole sizes? It seems that all aftermarket spheres are with onelayer membrane only and only original Citroen ones with dual membrane, so it would be same to use old green spheres if there´s nearly same specs on them.

[yoseff]

If there's a topic that deserves to be dig, this is for sure, one.
Learnt a lot more about how spheres work , specially on the damper side.
And what a better way to dig it up than bring a sphere (From a 204 C5 HA3+) that has a detail on the central hole that i never saw before?
Here i leave some pics. It's a 52 Bar front wheel sphere:

Interesting design...

(That way i can leave my humble contribution to this amazing topic, and also start following it)