Shock valving vs. re-charging

[EQuin]

Hi Folks,

I'm considering some 2.0 coil-overs for my daily driven, disco-ish Tacoma Prerunner that sees some occasional off-road use. Before I settle on a particular set, I was wondering what the difference is between shock "valving" and the pressurized gas charge within the shock. If I understand correctly, the valving of the shock is set by some washers inside the shock that control the flow of oil inside. Is that right? What is meant by "re-valving", and how does re-valving change or affect the shock's function?

Secondly, what is the purpose of the pressurized gas inside the shock? And how does increasing or decreasing the pressure affect the shock's dampening function? For instance, if the shock came pressurized at 150 psi, how does adding an extra 50 psi (for a total of 200 psi) affect the shock?

Thanks for any educational info. Take care,


Ed Q.
"If you're going through hell, keep going." Sir Winston Churchill

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[John_Bitting]

Experts let loose on this question. Since no name brand are mentioned it is acceptable, I say a lot of people can learn a lot from this Thread including myself... Kreg, Greg, anyone.. Thanks in advance.

[Mike_HKmtrsprts]

I know that re-valving a shock means changing washers to thicker or thinner to make it harder or easier for the piston to move through the oil, but I would like to know some anwers to your other questions. I always thought that the nitrogen was there to keep the oil from turning into a milk shake inside the shock. Im by no means an expert so some one let us know....

You must be Fast cuz I was HAULIN ASS when I passed you...

[EQuin]

Yeah, I was careful not to name any shock brands in the hopes of eliciting a brand-free, "shock science for dummies" response from our reknowned experts, me being a reknowned dummy - lol.

Thanks for the support and for bumping it up for me! And GOD BLESS AMERICA!!


Ed Q.
"If you're going through hell, keep going." Sir Winston Churchill

[EQuin]

Thanks for the info, Mike. At least I sort of understand the washer part. So changing to a thicker washer (which I take is also known as "re-valving") makes it harder for the piston to move through the oil? Or is it the other way around? And by making it harder for the piston to move through the oil, the dampening effect of the shock is increased, albeit at the risk of sacrificing a more comfortable ride?

Hopefully the other experts will chime in and explain more fully the purpose of the nitrogen gas, and how changing the pressure affects the dampening of the shock.

Thanks again and take care, and GOD BLESS AMERICA!!!


Ed Q.
"If you're going through hell, keep going." Sir Winston Churchill

[BIG_FAT_LOSER]

correct me if I am wrong:

nitrogen keeps pressure on the oil to prevent it from cavitating (bubbles, like a hand moving rapidly under water) a fast moving valve stack moving through oil creates a vacuum on the back side. The pressure keeps air bubbles from forming in this vacuum.

a shim stack or valve disk is like a flap on a big rig exhaust. Thin discs or washers cover the oil passages and the thinner or thicker the washes are, the more or less they flex to allow the oil through the passage and the slower or faster the valve moves through the oil on compression and rebound

reservoirs absorb hard fast inpacts (curb at 45 mph) that the vavle does not have time to respond to. the reservoir has a piston separating oil and gas. upon a fast inpact the valve cannot respond and the oil compresses into the reservoir and moves the piston and compresses the gas behind it. when the valve responds the gas pressure behind the piston move the oil (very little) back into the shock

shocks with out reservoirs use the gas as a sort of bump stop. as the valve cannot respond the gas compresses and allows the shock to move without locking

the amount of gas pressure basically makes the shock stiffer or softer under hard fast impacts.

bypass shocks usually have pistons without valve stacks. as the piston moves up oil is diverted through a hole in the side of the shock (not through the piston so it has nowhere to go) through an externally adjustable valve and back to the top of the shock. there are several passages at different points along the shock body as the piston moves upward. and each external valve can be adjusted (like a faucet) to allow more or less oil through it. there is also a passage on the rebound as well. these valves are one way flow.

Did I get an A? or an F?

<font color=red>PAT KAPKO</font color=red>
"DISCO FEVER"

[TimHayosh]

Here's my $0.02...

The washers are the valves. They are stacked on both sides of the piston (imagine a pyramid-shaped stack of washers that go from large to small diameter). Re-valving means you are changing the characteristics of the way the fluid is allowed to pass through piston. When the piston is in motion, the fluid goes through the ports in the piston and deflects the valve stack. The valves do not cover the ports completely. Therefore, at slow piston speeds, the valve aren't doing anything other than covering a portion of the port. At higher piston velocities, the fluid rushing through the port will deflect the valve stack. It is this deflection that you can alter by changing valves. Bigger (dia.), thicker valves will cover more port area and take more fluid pressure to deflect, i.e. a stiffer shock. Smaller (dia.), thinner valves (washers) will result in a "softer" shock. Keep in mind that there are valve stacks on both sides of the piston. This is how you adjust for compression AND rebound. Some shock mfgr's will have adjustable ports as well. Kinda like a jet in a carburetor. Others are just holes. There are also bleeder screws (in the piston) that can also adjust the low speed characteristics of the shock (when the valves aren't being deflected).

My understanding of the gas pressure (nitrogen) is that it helps to keep the fluid from cavitating when the shaft speed is high. In otherwords, when the shaft is moved quickly, a vaccuum (or just low pressure) is created on the back side. By having the fluid under pressure, it can more readily fill the void. I don't think gas pressure has a huge impact on the dampening charaterisics of the shock. You might be able to do some very fine tuning, but I don't think it will affect the shock in a big way. I think SAW and Fox recommend about 200 psi. I run mine at 210: big deal.

As an addendum, bypass tubes/valves only serve to change the valving characteristics when the piston is at a certain part of the shock travel. They allow fluid to port AROUND the piston valve stacks and go back to the back side of the piston. Once the piston moves past the last bypass port, all fluid must pass through the piston valve stack. Bypass tubes are directional. Therefore you have compression tubes/valves and rebound valves/tubes.

The only thing reservoirs do is add fluid QUANTITY. This allows the shock to disipate more heat. They have NO EFFECT on the dampening characteristics of the shock. On a street driven (or occasionally off-road driven) vehicle, reservoirs don't do anything for you. You will never generate enough heat to gain any benefit from a reservoir under those conditions.

So that's all I know about shocks. Flame away!

For more info, call a pro:
Lee at RaceShock Co. : 602-493-3700
Mike Arthur at Kartek: 909-737-RACE

[frankh]

You can not fill a non-reservoir shock all the way up with oil because you need some place for the oil displaced by the shaft to go. You need the fill that gaps with nitrogen or the oil will arrant (spelling ?). A reservoir shock pushes the extra oil into the reserve and the nitrogen pressure pushes it back. I think a by-pass shock still has valuing otherwise it would hydraulic when it passed the last tube. But we will all find out when someone that is knowable checks in.

[BIG_FAT_LOSER]

Reservoirs do allow for some heat disipation through radiating it, there is not enough oil flow between shock and reservoir to allow much cooling benefit. if there is no gas in a shock to absorb the fast hard hits it will lock hydroiclly, like putting your finger over the end of a syringe. you can move the syringe a bit because of the airspace. if it were filled completeley you could not.

<font color=red>PAT KAPKO</font color=red>
"DISCO FEVER"

[vwguy]

everything here is right
as pat said the resivoir kind of acts as a bump stop when the fluid can not flow through the piston fast enough the piston in the resivoir compress's the nitrogen and then bounces back
i believe frank is right if there was no valving in the piston of a bypass shock it would lock up having no where for the fluid to go if it passed the last hole

how ironic is it that most people slow down for speed bumps yet almost all of us here im sure pin it