Modifying midvalves on a KYB(and others)

[svi]

What would happen if we kept the check plate but were to replace the spring with one of sufficient force to provide resistance, would this act just like a shim stack?

 

[JTT]

SVI, I think that would have to be a fairly significant spring. I mean there is a lot to pressure here. And even if the spring would work, I think you would still have the same issues as closing the float on a "normal" midvalve.

 

[John Curea]

SVI,
Yes , but the spring would have to be considerable, the DRZ uses a pretty stout spring (compared to whats on a normal MV) and it is still pretty much "just a checkplate".

I'm sure the spring would have a different damping coefficient than a shim stack, MACE, could elaborate on this better I'm sure.

KXVET

 

[svi]

I agree it would have to be quite a substantial spring what interests me is the opening characteristics of a fairly rigid plate controlled by a spring compared to a shim stack, I realise that this is dependant upon the build of the stack, but to apply some bizarre logic if a stack acts like a leaf spring then wouldn't a coil spring offer better control ?

 

[marcusgunby]

SVI if we used a coil spring of sufficiant strength i guess it would work but it is not tunable like a shim stack-after all that why the shim stacks came about:D

 

[svi]

Marcus,
I don't see why a spring couldn't be tuned with different amounts of preload, different lengths to permit float and different spring rates e.t.c. Just like shock or fork springs.

 

[marcusgunby]

You can tune a spring with different preload but its rate will always be the same -unless its a progressive(and i hate progressives:p )a shim stack we can tune to be initally soft and then infinitly hard or something else.If a spring could work wouldnt we have them instead of shim stacks on base valves and rebound stacks.:eek:

 

[svi]

Marcus,
I understand what your saying but in this one particular instance The shims do not work in the usual manner. As I understand it the main purpose of a shim stack is to seal the piston port and then yield once a set force acts upon it, the build of the stack then controls the rate of opening, the most important part of this being the initial yield point. With the compression side of a midvalve there is no initial yield point as soon as the piston travels in a compression direction the ports are open, if you didn't need the shim to seal the ports in a rebound direction you could leave the shims set against their stop away from the piston. The only reason I can see to have a stack that is set away from the piston is that there is such a significant flow that it can be controlled from a distance with the shims deflecting in a controllable range. In your original idea you suggested building up a stack against the piston, this I suspect is not done because of the large deflections involved resulting in the shims taking a permanent set. My theory with a spring was to enable geater control over the initial yield and opening of the port but still allow for the large deflections necessary. If the check plate were delta shaped this would signifcantly reduce the affect between the cartridge sidewall and the shim and the damping would be controlled by the rate of opening of the ports. Could you get the required controll from a spring ?
Does this make any sense or am I disapearing up my own orifice ?:eek:

 

[JTT]

SVI, your thinking makes sense to me ;) But I think that, because the midvalve seems to require significant "free bleed" (ie: unmetered, or nearly unmetered fluid flow, in order to not act upon the "low speed" portion of the stroke that it would mean that your initial "yeild" point would have to be very light, then suddenly get stiffer. Maybe a short stiff spring inside a longer light spring might give a more accurate comparison? Either that or put larger free bleed holes in the piston to compensate.

Then again, I may be way off base :think

 

[svi]

JTT,
The dual spring idea was something I was thinking along the lines of, with the end result being metered bleed allowing for a reduction in low speed damping on the base valve. It does mean however that it perhaps becomes an over- complicated arrangement and may not even be physically possible, but it is an interesting concept.

 

[marcusgunby]

SVI i think your system may work but to what end-will it be cheaper/easier/more tubeable/ more reliable than the present set up,i feel we have a design with no reason-its an interesting idea though:D