Cylinder Valves

[terry hay]

Jeremy
I agree and disagree with some of your points. Firstly in order to achieve as similar feel with different pistons your'e right! You do require a similar total energy effect. But piston port diameter will always have an effect on flow. High flow pistons don't require more shims, they require less. The pressure is dispersed over a greater area of the shim resulting in more spring force being generated from that shim with less overall deflection. (Distance from the piston face.) Also any orifice creates friction loss affecting flow rate. The smaller the orifice, the greater the friction loss. A piston with smaller ports concentrates the flow in a smaller area creating greater pressure. This is similar to a woman with high heels and a woman in sneakers walking on a cork floor. Both women may be of similar weight, but one is applying a lot more pressure to the floor than the other and more likely to depress the surface. An easy test for high flow / low flow pistons is to use them both with the same shimstack and feel the difference. And you will feel it. As a manufacturer and retailer of pistons yourself, I'm suprised you would make the comment that they create no effect. At the end of the day, it's the final result that matters. If you can achieve rider satisfaction, the fact that you have achieved it is more important than how. (To the rider)

 

[terry hay]

Jeremy
You say the cyclinder valve has a place in the future and that KYB has not finished with it yet. I applaud your faith in the product. Perhaps KYB will produce something viable with it in the future and we will see their efforts reward their customers loyalty. But at what point do we accept a product as being ready for production? There is little doubt that the CV has created a backward step since its inception in 98. I don't think it is fair that the public is asked to suffer these results while they wait for KYB to get it right. Unfortunately as much as companies are in business to make motorcycles, they're also there to make a profit. We see many new features introduced which provide sales tools rather than tangeable results. In suspension alone we have seen such gems as, anti-dive forks, air assisted forks, the BASS system. The Japs have created a need in us to have the latest and greatest and not always to our advantage, but always to theirs. You're 100% right when you say technology will always win in the end. In the mean time someone needs to keep "the powers that be" honest. Where do you see the future of the CV?

 

[Jeremy Wilkey]

Terry,
I don't think my products have anything to do with the discussion on the table. I don't spam on this board.. Secondly whether its one of my seminars or a discussion of suspension principals my products simply exists within the context of theory, so I'm only explaining the theory.. If you go back and read my post you'll clearly see I created a frame work that sets the answers up only to explain the differences relative to the question.. I said "if they where to feel similar they are storing similar total energy as they create similar valve orifice area" you agreed yourself.. So yes I believe different valves have very different characteristics, but to better explain the concept I stuck to a contrived example to illustrate the differences.. As noted in "this is important when you consider piston design"

Now on to other stuff...

Originally posted by terry hay
Jeremy
Firstly in order to achieve as similar feel with different pistons you're right! You do require a similar total energy effect. High flow pistons don't require more shims, they require less.

They do? I'd like you to clarify this point.. I'm very confused by this.... How can a valve control orifice area with greater area and less shims?

Originally posted by terry hay

Also any orifice creates friction loss affecting flow rate. The smaller the orifice, the greater the friction loss.

Friction loss? That must be a small and long port... I don't think frictional forces have much to do with any practical application that you or I work with, as it realtes to this topic.. The valves we work with are not even close to restrictive and the ports are quite short. Text book equation stuff, with good applications but minimal in our case.. And you agreed with me earlier right?

Originally posted by terry hay
"Firstly in order to achieve as similar feel with different pistons you're right! You do require a similar total energy effect."

Well if we are storing similar energy and we had substantial friction loss that would produce less stored energy by your logic right? So well we must be losing a similar value due to friction small or big ports.. Which brings us back to point we are not even close to a fluid flow threshold..

Originally posted by terry hay

A piston with smaller ports concentrates the flow in a smaller area creating greater pressure. This is similar to a woman with high heels and a woman in sneakers walking on a cork floor. Both women may be of similar weight, but one is applying a lot more pressure to the floor than the other and more likely to depress the surface. An easy test for high flow / low flow pistons is to use them both with the same shim stack and feel the difference. And you will feel it.

My point exactly, but I'd like you to extrapolate on how you feel this difference is achieved?

Originally posted by terry hay


As a manufacturer and retailer of pistons yourself, I'm surprised you would make the comment that they create no effect. At the end of the day, it's the final result that matters. If you can achieve rider satisfaction, the fact that you have achieved it is more important than how. (To the rider)

As you can see I defiently said nothing of the sort.. But I do think that any valve and combo can have the same total area, the same total coefficient at some speed, just not over a range of speeds and that is where the real science and art of suspension meet..

BR,
Jer

 

[Jeremy Wilkey]

Originally posted by terry hay
Jeremy
You say the cyclinder valve has a place in the future and that KYB has not finished with it yet. I applaud your faith in the product. Perhaps KYB will produce something viable with it in the future and we will see their efforts reward their customers loyalty. But at what point do we accept a product as being ready for production? There is little doubt that the CV has created a backward step since its inception in 98. I don't think it is fair that the public is asked to suffer these results while they wait for KYB to get it right. Unfortunately as much as companies are in business to make motorcycles, they're also there to make a profit. We see many new features introduced which provide sales tools rather than tangeable results. In suspension alone we have seen such gems as, anti-dive forks, air assisted forks, the BASS system. The Japs have created a need in us to have the latest and greatest and not always to our advantage, but always to theirs. You're 100% right when you say technology will always win in the end. In the mean time someone needs to keep "the powers that be" honest. Where do you see the future of the CV?

Terry,
I spent some time on the topic from 2 above and I've got to get some work done so tutealu for now, but give me a break on this last post.. Are you really serious about the above comments? Thats some really harsh, and off, unlogical things to say.. Grandted there are some kernals of truth, but overall as it realtes to the topic its beyound lame.. I'll fire back if you want, but really thats like the brick "literally" that hits the backboard.. Where not even playing basketball anymore, and this has been a fun dialog.. Tell me your just having fun playing devils advocate.
BR,
Jer

 

[drehwurm]

Servus,

I'm not sure if I'm loosing my mind or beginning to understand so please be a little more patient with me.

.) the damping created is directly proportional to fluid flow (amount of fluid which flows in a given time span) which in return is directly proportional to orifice size (area - 2 dimensional?)

.) orifice size depends on piston port size and shim deflection

.) piston port size is in general LARGER than orifice size, thus creating no additional damping

.) for a given amount of damping (fluid flow) small piston port size means more shim deflection and larger piston port size means less shim deflection

Lets make some assumptions (from the depth of my confused mind):

1a) pressure on the forks for a given situation is constant. Thus pressure on the shim stack, regardless of port size, is constant. I do think that above analogy with the women and different shoes does not apply here. Why - simply because the shims are not made of cork. Just imagine the woman walking on a big steel shim - pressure on the shim would be always equal to the weight of the woman (and distance from the pivot point) regardless of the shoes. The point here is, that if you compress the forks with the force x, pressure on the shim will be x/hydraulic leverage (where the hydraulic leverage is NOT influenced by port size).

1b) same pressure, same shim stack means same shim deflection regardless of piston design. BUT if shim deflection stays constant this would also mean less orifice area (more damping) on smaller port size piston and vice a versa more orifice area (less damping) on larger port size pistons. Now if you want constant damping you would have to lighten the shim stack (more deflection on constant pressure) on the smaler port piston and stiffen the shim stack (less deflection on constant pressure) on the larger port piston. This would conclude with the observation that "low flow" (small piston port) pistons feel stiffer with the same shim stack vs "high flow" pistons.

2a) If pressure on the shim stack really varies with port size (AND NOT port design which is a completely different topic) I have no idea and give up.

Michael

 

[terry hay]

Micheal
Don't despair! The analogy of the women on the cork floor was simply to demonstrate how a force or weight could be supported if the distribution of force was adequate. You mention "leverage" and this is also a key factor as to how the force is managed. Smaller port pistons usually have the ports located close to the outer edge of the piston/shimstack. Lager port designs naturally see the fluid flow directed to a higher proportionate area of the shimstack. Therefore the smaller ports concentrate the force to a smaller area applying more leverage to the shimstack and allowing it to flex easier. The larger dissapation of force from the high flow piston means it can be supported more effectively by the shimstack and yes the total number of shims can be less. When the shimstacks open in both cases we will see the shims distort/deflect in different ways. The shims on high flow pistons will not have to bend as far to create the same total port area as the low flow design. Any one who has ever installed a high flow piston would have noticed how much lighter the new shimstack was compared to stock. Marcus???

 

[marcusgunby]

Well terry you have lost me, i was always under the impression the high flow piston has a fair few shims(maybe this was the GV1?)
now to expand my thinking its not good for anyone to compare to a std piston with a std shim stack-these have many many shims, but are also harsh, so what i have done is got a shim stack for a RT 02 Cr125 fork i rode in the US.This does use less shims than a std fork and it has no mid as well so its true to say a high flow can have less shims than std, a low flow also uses less shims than std, and i have used low flow stacks on a std piston and it worked.
So in conclusion everyone is using less shims than std, this tells me std is crap, i know this as my wrists hurt and i struggle to ride a std bike these days.

Now who can use the least shims (assuming the same mid) std piston ,low flow or high flow thats the question;)

 

I would like to see a test done with the same piston and same stacks, with just the port size smaller and then larger than std, keeping the point of force the same.

 

[terry hay]

Marcus
The test you talk about is exactly the thing that will best demonstrate what I'm talking about. Take a fork comp valve, switch the piston to a high flow unit whilst maintaining the original shimstack and ride. You will notice the difference. It doesn't matter wether the original or latter performance was good or bad, only that a change has resulted. Sometimes we can theorise endlessly but at the end of the day things can best be solved by actually having a go and getting our hands dirty.
Terry

 

[marcusgunby]

terry the problem i have is three fold LOL
1) i have no high flow pistons
2) the high flows have (on a GV) a different top shim size
3) its raining every day and i hate it:(
but i think you are correct they would feel different.

 

[terry hay]

It's time you stole a loaf of bread and got yourself transported to Australia my friend. Sunshine all year round and plenty of riding areas

 

[bclapham]

i heard the land of Auz loves delinquents and crooks!:)

 

[Jeremy Wilkey]

Guys,

I've got to step back from this for a minute, but you guys are going off into la-la land.. Heres the deal apples to apples a valve works by controlling the area of effective orifice..

An effective orifice is created by the multi dimensional space that's created by the shims and the piston as the shims bend..


As we bend shims they store energy.. The more we bend them the more energy they store.. Bending 1 shim a large value could equal the force of many shims bent a little.

When we stack washers we are making a stiffer collective spring...

Now if we have a piston that has large area then when a shim bends even a little bit it creates a large effective orifice area.. A bigger effective orifice means softer suspension.. Is everyone still with me..

Now the faster the fork moves the more pressure that is created and the greater the stack opens given the same shim stack..

The more the stack opens, the larger the area of the effective orifice, and also the faster that the orifice gains area, berceuse its growing in multiple dimensions..

So when we need to control this orifice area to produce a certain damping coeifecnt defined as a total orifice size we must stack shims on to limit the orifice from growing to quickly and making the suspension soft.. If we limit it too much then the suspension is hard.. Make sense?

The shims as they deflect are just like a spring.. They are storing energy...

Now for the next bit....

Lets say we have a valve that produces larger deflections for the same volume of fluid. This valve will have less exposed area when the shims bend. The shims must bend farther to create the same orifice area, as a high flow piston with a larger potential exposed area... Instead of bending many shims a small amount to create area X and Force of shim resistance Y we are bending a few shims to larger amount to create similar area x and force values..

That being the case within a range relevant to the application a higher area piston must use more shims to control the same total orifice area as a piston with less area and more deflection.. The lower flow piston bends the shims more to get the energy it needs to resist rate of growth and high flow bends many shims a little to get the same stored energy...




Jer

 

[steve125]

Terry, after you have educated Marcus then you can call him "Mini ME" :)

 

[bclapham]

so who is doctor evil???

 

[steve125]

Freaking LOL Bruce!!! :worship:  it's Terry and Marcus!!!! :yeehaw: :)

 

[terry hay]

Carefull man - We've got your mojo

Where do you get those jumping bananas?

 

[drehwurm]

Servus,

That being the case within a range relevant to the application a higher area piston must use more shims to control the same total orifice area as a piston with less area and more deflection.. The lower flow piston bends the shims more to get the energy it needs to resist rate of growth and high flow bends many shims a little to get the same stored energy...[QUOTE/]

Didn't I say that? Maybe I just wanted too, but at least I can understand it.

Terry: Yes, I'm aware of the leverage effect of different port designs. In my example I was thinking of the ports as concentric circles of different diameters.

Marcus: What have Austria and Australia in common: They both have much better weather than England (especially since I have my new bike - the weekend was GORGEOUS for riding)!

Michael

 

[svi]

Jer, Correct me if I'm wrong, I think the point that you are making that people have missed is maintaining an "identical damping coefficient throughout a given speed range."
In practice most high flow set-ups I have seen run less shims than a low flow because the designers are looking for a "lower damping coefficient."
I'm purely speculating that Jer likes a very linear progressive increase in damping force that would result in a relatively steep graph, whereas Terry likes an increase in damping force which would give a less steep graph.
It's controlling the rate of increase in damping force that is critical to good suspension and there are a million and one thoughts and ideas on the best way to achieve this.

 

[terry hay]

Jeremy has certainly provided food for thought and has me re-evaluating my own opinions. Variables such as discharge velocities surface areas and leverages still enter the equation and require there own place in all of this. But this is what it's all about, right?

 

[georgieboy]

Terry, is right about the high flow versus the low flow pistons. Aslong as the point of impact is the same, and that is normally the case. The piston holes are always positioned along the outer edge of the piston due to the opposite rebound shims. The high flow(smaller hole) pistons will need more shims to create the same damping bearing in mind that the holes itself are not obstructive part in this. When holes itself become the obstructive damping part I feel less shims may work all so.
I need few rebound shims as the holes are only 3mm small, wld i use it as a comp piston the holes wld probably create too much damping force, to the point feeling harsh. I wld think it wld become and switch on off.

 

[georgieboy]

And to correct myself, Jeremy is absolutely right too.
In the last part of jeremy's reply he also is saying the relation between the shimstacks, regarding the low-high flow pistons.

So now that we have said the same about the shimstacks the problems lies in how to make this work for a sertain rider. Do we need high-bending shimstacks or do we need lower bending shimstacks to create the nessary damping curve. Maybe we need a fresh topic to start this off.
What are the pros and cons of the different shim-stacks?
We already have said a lot about it, specially Jeremy, in the past, but maybe we have to fresh things up again. There is fresh blood amoung us. Let us use that.

 

[russ17]

Hi guy's

One thing that comes to mind on this issue of high flow -low flow, is the face shims are being used here. Weather its a .21 or a.24. Now the high flows that I have seen they use a .21 and the low that I have seen use a .24. IMO the .21 would have higher spring rate then the .24 of the same thickness. ( leverage points change)So how do we compare the 2. Both are contolling the growth area with different spring rates in all reallity.

Russ

 

[Jeremy Wilkey]

Guys,
I'm glad this back to a suspension forum... Because I thought we are talking about Theory, simply about properties of valves, and how they create area..

And as GB, SVI, and Russ, pointed out we have some contributing practical matters that brings in a certain amount of confusion.. As always I talk theory and theory doesn't care about anything other than the relationships of variables.

So yes many times less damping appeals to some and smaller leverage means more stored energy for equal deflection etc.etc.. (BTW SVI I'm all about digressive but we can talk about that later.)

To clarify if we have a higher flow valve and lower flow valve and we need to produce a specific damping coefficient with both, the lower flow valve will bend the shims more than the higher flow valve.. Therefore if the shim stacks where the same, the lower area valve could not produce the same damping rate because it could not deflect the shims far enough to generate equal area.. However if we where to reduce the effective shim strength then we could allow the stack to open enough and create sufficient area at the same speed. (Maybe a dynamic example might help.)

BTW BG what your saying is correct only in a limited scope.. Its wrong in practice because we are not starting with an open valve..And we have to consider the whole range not just a small highspeed only portion of it.. (this BTW is why low flow works in our apps when we have high speed the valve is blow wide open due to pressure and we have almost unlimited total area and that makes a shallow line SVI) We are starting with a closed valve that must produce significant low speed compression. If we have a large area valve and we must control low speed because of all that area we must put many shims on it to control this rate of area growth.. Simply put its a force verse area equation, but since the fork is moving slowly we have no velocity induced pressure jet going on and we will have little deflection in either case which makes the point in question mute..

Whats the difference between them? I often tell people high or low flow is a stupid argument. Its about maximizing the deflection properties.What do we mean by this? Specifically the faster the valve can size itself up or down relative to speed changes, and how efficiently it can regulate one infinitely minute adjustment in size as a change in speed to another..

This changes based on our speed ranges, and our volumes.. One valve with small ports in a fork means nothing to a fork with a smaller fluid volume. So all I think the point is we need to change the pistons properties to allow for the maximum control of our deflection properties, based on our requirements. To say high flow or low flow is better is ignorant, without examining the context of the design..

The differences in the way a high flow and low flow gain area, and regulate that area is very different. For instance with a midvalve piston the bigger area the better as we can reduce lift and gain regulation of the area, with a low flow in a midvalve we would never be able to effectively the rate, and varying degrees of area with any degree of control due to the massive pressure that would be generated.. So as you can see the real goal is aligning the variables to the context of the design!

BR,
Jer

 

[PMK]

I've followed this along with others and have seen it go from the cv's to a hi / lo flow discussion. If it's possible does the data easily exist to show fork velocity, which could be interpeted into into fluid displacement. I would suspect that if the shockclock data aquisition system could provide a maximum value we could confidently see the comparison of piston orifice to volume flow. Granted this could vary for different size rods but could still be calculated and have a buffer built in.

I can't say I agree with both of you (JW, TH) on all your points but will run with more deflection can be control flow better. Kind of like having fine threads vs coarse threads. The less deflection dumps the bucket of water while the more deflection pours the water out, bad analogy but works for me. They both get the job done in a similar time one is just more controlable.

As for the CV it appears the issue is more consistency. That said, hypotheticaly, why not provide a small bleed jet to purge air from the cartridge upper end. And to provide a partial backfilling to reduce oil seperation from the midvalve flow which then is emulsified fluid thru the rebound valve on the next extension, use a valving arangement as in the old school fox shocks or works performance setup. This along with a standard bush would allow for more consistency, and some tunability to the CV.

PK

 

[terry hay]

PMK
your idea sounds interesting although the location of bleed and valves is not specific. Are you saying you would place a bleed in the cylinder valve itself?
You may find back filling of the cartridge would be difficult without creating a low pressure area between the midvalve and the top of the cartridge. The 97 YZs simply had a shaft bushing which allowed a small amount of fluid to bypass around the damper rod which assisted with purging of air. I'm not too familiar with Works Performance shocks as I have only worked on two of them. Is the valve you talk about similar to the spring and ball system they use for compression control?
Regarding the valve flow issue I understand the point Jeremy is making about the rate of deflection of the shims increasing the stored energy. But this is relative to distance from piston face and allows little consideration for the actual area of the shim that is bending. Surely it is possible to have the same amount of stored energy if a greater area of the shim was subject to deflection yet over a shorter distance. The port size clearly affects discharge velocity which would also affect the amount of deflection required. I can particularly see an advantage in a smaller port if you were constructing multi stage valving. I know pro-action tout the advantages of three stage stacks, but I have never found them very capable in a fork application with a high flow piston.