Emulsion shocks vs Bladder shocks
 

Hi all, I know what the difference is between emulsion shocks and bladder shocks. But I don't know technically the difference in how they function. Can anyone explain clearly, or point me towards a good technical explanation on the way each works? The advantages/ disadvantages of each?

Thanks!

Either shock has to have a certain amount of air in the shock body to allow for the volume compensation when the shock shaft enters the shock body. Imagine filling a glass with water then dropping ice cubes in the glass. Since the shock oil can not be compressed to allow the shock shaft to enter the shock body, a certain amount of air is necessary.
The difference between the bladder and emulsion shocks is the air in the bladder shock is kept separate from the oil, and the emulsion shock allows the air and the oil to mix. I have run both and prefer the bladder style myself. I believe the bladder shocks are more consistent over a longer period of time.
Hop this helps.

AHA!:sweat: I had forgotten the shaft that takes up volume!:nod: So the air is in there to be compressed and compensate for the shaft... And basically, the emulsion shock doesn't have a divider between the oil and the air. So air can mix with the oil. Doesn't this create more turbulence and hinder smooth damping?

I mean, what is the use of bleeding the shocks to get all air out of emulsion shocks if it's going to get back in there? I too have switched to bladder shocks and now understand why they are soo smooth, and stay smooth.

So what is the advantage of emulsion shocks, appart from the lower production cost to manufacturers?

Thanks for the enlightenment!

emulsion shocks offer more traction ..

They do not have to push & pull a rubber bladder on each stroke.
Which means they are smoother than and work better than a shock with equip with bladders...

Bleeding emulsion shocks is necessary to remove excess oil. If you fill the shock up completely with the shaft all the way out. Put the cap on and see what happens. The shock will not move, the condition is called hydro lock.

As far as advantages of an emulsion shock. I'm not sure there are any after switching to bladder shocks. :D

Emulsion shocks NEED air in them to work correctly. If anyone bleeds all the air out of the shock - they are making a mistake.

Bladder shocks have a stronger rebound (due to the rubber bladder trying to return to its original shape), so don't tend to ride the bumps as well as the emulsion shocks. I've tried bladder vs. non-bladder in the Lazer ZX-5 and the bladder seemed to keep the car "up on its toes" and took away some suppleness over the bumps.

Another thing to be aware of with bladders is that the shaft may hit the bladder at full compression if you put them in a shock that was intended to be an emulsion type.

I run the emulsion style when I am after less rebound.

Yeah, I explained poorrly on taht one... I meant what is the purpose of getting all the bubbles out from under the piston while bleeding if air is going to get back in there anyways!

I've found my bladders much much smoother than the emulsions... Just my experience...

I can bleed my bladder shocks to have little to no rebound at all. If a bladder shock has too much rebound, it's due to too large of a pocket of air in the bladder. Kinda like having a small balloon under the shock cap. To prevent the piston from hitting the bladder, I use some old shock O rings as external travel limiters. Works great.

Maybe it's just me but to get as little rebound as posible with bladder shocks they wind up with to little oil in them to stop them from emulsifing. Am I doing something wrong or what. When I build my shocks with enough oil to get the smooth feel I want and can tell that they're not sucking air they have more rebound than I want......After 20 years I still hate shocks:lol:

You should get the bubbles out from under the piston before bleeding emulsion style shocks because you want to have the smallest amount of air possible in the shock while still allowing it to work properly. If you put the shock together without getting rid of the air pockets from under the piston and whatnot, air will seep into the body of the shock causing the shock to have too much air in it. Too much air can cause problems with consistency.

I know that part:D Just seems to be such a VERY fine line between 1/2 inch rebound and that "sqwuush" feeling at the top of the stroke.:lol:

Ahh, that makes sense.

Thanks everybody for your constructive contribution to this subject!

Since emulsion shocks allow the air to mix (emulsify) with the oil, the two mediums (air & oil) cause the mixture to become lighter/thinner than the measured oil weight. I don't know the math behind this, but this reason alone makes it incredibly important to get the exact same amount of air in each shock.

Too much air in one and it's mixture will be thinner than the other. The air volume can be evaluated by measuring rebound spring, but both shocks need to be the exact same temp since temperature directly affects air pressure and both shock's o-rings/shafts/pistons need to have nearly identical resistance (such as after a rebuild). For temp, hold both in your hand or let them sit for a few minutes before checking rebound.


Here's my thoughts on bladder systems:
I don't believe that saying "bladder shocks have more rebound" is 100% correct. Yes the bladder wants to return to its original shape, but its a thin piece of rubber, the majority of the rebound spring comes from air pressure. If the bladder happens to trap more air than your emulsion bleed method, then of course it will rebound more!

Here is a comparison using my Team Associated shocks as an example:

When you build the Team Associated shocks, you can't just fill them with oil and close them up. If you do, they hydro lock about 70-80% compression because the air is compressed too much. You have to leave the cap loose and squeeze out the excessive oil until you get full compression stroke, and the compressed air pushes the shaft back out a little bit. At full extension, the air is expanding under vacuum. Turning the shock upside down makes it feel like there's too much air because it has expanded and you feel it when the piston is in the air.

I then converted them to the VCS bladder system and added a couple 1/32 spacers under the lower spring seat to shorten the stroke just a hair and prevent crushing the bladder (without at least one, the shaft does hit).

With the bladder conversion, if I build the shocks at full extension, they will hydro lock about 70% travel, just like the emuslion build method, again not enough air volume... Associated's shock design doesn't have enough volume to handle being built with the shaft at full extension with or without a bladder. The emulsion method compensates by having you compress the shaft and squeeze out some oil. Can't do this with the bladder method. Instead, because I still have to compensate for the shaft, I build the shocks with the shaft approximately 30-50% compressed when I close them up.

This way the bladder expands a bit under full extension, and this suction/pulling effect tends to "soften" the spring rate at full extension, beneficial for rough surfaces. The bladder offers the least resistance around the middle of it's stroke.

With either method (bladder or emulsion) they can be built to rebound the same. I bet the "extra grip" some of you are noticing with the emulsion method comes from the oil mixture getting thinner from blending/emulsifying with the air... Comparing apples to apples (same shock) keeping the air/oil separated by a bladder has the effect of using thicker oil since the air doesn't thin out.

RC shocks are so ridiculously simple, and the fact that some require air and oil to be mixed leaves me dumbfounded. Motorsports shocks of any genre are so incredibly sophisticated with shim stacks, separate high and low speed compression and rebound adjustments, separate reservoirs and adjustable nitrogen piston pressures and volume, high pressure X-seals and directed oil flow valves... Some shocks (such as many mountain bike forks) use an "open bath" system... However, the oil is sucked from the bottom through the damper's chambers and this helps prevent mixing. One constant remains, allowing air and oil to mix is a big no-no.

A very thorough analysis - and you are right to observe that the things that seem to work in RC are often wrong in engineering terms.

But I do think you are approaching your damper assembly wrong - it is very easy to build a bladder shock at full extension - just press the bladder into place and put the cap on. Should not be any hydrolocking anywhere in the stroke. It's also pretty easy to build the emulsion shock at full extension too. Just work out how much oil to put in before fitting the cap (in my eyes, just up to the brim with a concave meniscus works about right). Bleeding the shocks at part compression just makes the shaft pull back in from full extension - not desirable in my book.

Personally speaking I don't think emulsion damper rebound is consistently tunable - overfill the shock and it will leak, underfill it and it may get airlocked. With bladder shocks, you can tune rebound with o-rings or foams in the air gap, or stiffer/softer bladder rubbers.