An alternate method of getting air out of AHC system

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Hello Mudders! I bought a 2002 LX470 a couple years ago, and ever since, I had been following this forum for all my maintenance on the truck. Recently the ride had gotten rough. First I tried changing fluid but the ride did not improve. I finally bit the bullet and purchased 4 AHC globes from Impex. Installation of the globes went smoothly. I only bleed out about a quart of AHC fluid from the 4 corners to release the pressure from the system before unscrewing the old globes and screwing the new globes on( Note: I did not bleed the accumulator ). Immediately I took the truck out for a test drive. The ride is improved but underwhelming. Surely there must be a lot of air pockets still in the system.
Since I got relatively new fluid in the system, I decided to try removing air from the system without bleeding more fluid. Basically my method relies on Henry's Law which states the amount of a gas absorbed into a liquid is proportional to the pressure on that gas. These are the steps :
1. Start engine, raise vehicle to H. This ensures maximum amount of fluid get drawn into the system.
2 Stop engine and wait 30 min. This is to ensure sufficient time for the air pockets to be absorbed into the fluid.
3. Start engine and lower vehicle to L. This would expel maximum amount of fluid to the reservoir.
4. Stop engine and wait 30 min. This allows the fluid in the reservoir to air out to the atmosphere.
I did 5 cycles of these 4 steps and then took the truck out for a test drive. The truck drove wonderfully. For the first time since I bought the LX, I fully experienced the smooth and excellence ride that Lexus is known for.
 
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Interesting logic and procedure. I’ll let the AHC experts chime in here but if you’re coming onboard to provide this info as your first post you’ve earned your mud badge by my book.
 

ramangain

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Chances are pretty high that nitrogen gas has an extremely small solubility (coefficient) in OEM AHC fluid.
 
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Chances are pretty high that nitrogen gas has an extremely small solubility (coefficient) in OEM AHC fluid.
Normal air is 80% nitrogen also. However, the pressure in a working AHC system is extreme. Atmospheric pressure at sea level is only about 14.5psi. At working pressure, AHC system ranging from 5-10MPa(725 - 1450psi). Even if a little air is absorbed in AHC fluid at atmospheric pressure, the amount of air absorbed in a AHC system can be 50-100 times higher.
 
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Will be running through these cycles today just because it's something easy to do while the truck is parked. Makes sense that it should work.
 

suprarx7nut

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Chances are pretty high that nitrogen gas has an extremely small solubility (coefficient) in OEM AHC fluid.
Perhaps related. Something interesting I noticed when I first flushed my AHC fluid after buying the car: I used a syringe and could draw a lot of vacuum on the fluid from the reservoir. As I pulled fluid from the reservoir, I could see bubbles come out of solution. Not just a few. A TON. Here's a shot of little vacuum (holding camera, so there's little to no tension on the syringe beyond the O-ring friction of the plunger).

I think there's something to be said of gas being trapped in that fluid. I'm unsure of the method in the OP, but I think it's intriguing. My little experiment showed that even after resting in the reservoir a while, there was a lot of potential for trapped gas in the fluid. Perhaps that's an inherent property of the fluid, but it seemed a bit wild how much gas was coming out as I pulled that plunger back.

1631029974310.png


1631030016433.png
 

ramangain

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Normal air is 80% nitrogen also. However, the pressure in a working AHC system is extreme. Atmospheric pressure at sea level is only about 14.5psi. At working pressure, AHC system ranging from 5-10MPa(725 - 1450psi). Even if a little air is absorbed in AHC fluid at atmospheric pressure, the amount of air absorbed in a AHC system can be 50-100 times higher.
I don't disagree. But I'm hinting to keep in mind that for Y = A*X, even huge values of X may not overcome A so Y takes on meaningful values.

Without A, we have no feel for Y. Does anyone know the value of A?
 

ramangain

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Perhaps related. Something interesting I noticed when I first flushed my AHC fluid after buying the car: I used a syringe and could draw a lot of vacuum on the fluid from the reservoir. As I pulled fluid from the reservoir, I could see bubbles come out of solution. Not just a few. A TON. Here's a shot of little vacuum (holding camera, so there's little to no tension on the syringe beyond the O-ring friction of the plunger).

I think there's something to be said of gas being trapped in that fluid. I'm unsure of the method in the OP, but I think it's intriguing. My little experiment showed that even after resting in the reservoir a while, there was a lot of potential for trapped gas in the fluid. Perhaps that's an inherent property of the fluid, but it seemed a bit wild how much gas was coming out as I pulled that plunger back.

View attachment 2779954

View attachment 2779955
Excellent demonstration!
 
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I don't disagree. But I'm hinting to keep in mind that for Y = A*X, even huge values of X may not overcome A so Y takes on meaningful values.

Without A, we have no feel for Y. Does anyone know the value of A?
Empirical evidences suggests that a significant amount of air or nitrogen can be trapped in AHC fluid under high pressure. As suprarx7nut observed in his post, I also observed white foam on the surface of my LX's AHC reservoir immediately after my first few cycles of raising and lowing my vehicle. Before that, when I bled the pressure from the system prior to removing the globes, I used a clear plastic tube attached to bleeder nipple dropping it into a container. I did observed clear fluid coming out at the top, but by the lower haft of the tube, a lot of tiny white bubbles already forming in the fluid. That probably was the nitrogen escaped from my blown old globes.
I would propose an experiment where 1 litter of AHC fluid would be placed in a container along with 1 litter of air at normal atmospheric pressure. The container would then be pressurized to 145 psi. After perhaps 1 hour, the volume of air remained would be measured and then compare with another 1 litter of air that was also was pressurized to 145 psi. The difference between the two volumes would tell us how much of the original air is absorb in the fluid. We then can even calculate the coefficient of the AHC fluid. Of course we need someone with access to lab equipment and willing to do this. If any member would like to attempt this experiment, I would love to know the result.
 

ramangain

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Empirical evidences suggests that a significant amount of air or nitrogen can be trapped in AHC fluid under high pressure. As suprarx7nut observed in his post, I also observed white foam on the surface of my LX's AHC reservoir immediately after my first few cycles of raising and lowing my vehicle. Before that, when I bled the pressure from the system prior to removing the globes, I used a clear plastic tube attached to bleeder nipple dropping it into a container. I did observed clear fluid coming out at the top, but by the lower haft of the tube, a lot of tiny white bubbles already forming in the fluid. That probably was the nitrogen escaped from my blown old globes.
I would propose an experiment where 1 litter of AHC fluid would be placed in a container along with 1 litter of air at normal atmospheric pressure. The container would then be pressurized to 145 psi. After perhaps 1 hour, the volume of air remained would be measured and then compare with another 1 litter of air that was also was pressurized to 145 psi. The difference between the two volumes would tell us how much of the original air is absorb in the fluid. We then can even calculate the coefficient of the AHC fluid. Of course we need someone with access to lab equipment and willing to do this. If any member would like to attempt this experiment, I would love to know the result.
I do, but I'd probably get disciplined if I contaminated the equipment with AHC fluid. Good experiment though!
 
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On mtn bikes that used certain hydraulic fluids in the brakes, I would get better performance from degassing the fluid under vacuum as shown here. I would degas in the syringe until no large bubbles would form and gather. When reading any of the issues people are having, my first thought is vacuum pump... good demo here!

this was a little known trick in the bike world (long time hobby and former mechanic in the nineties) for brakes that eluded easy set up.
 
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This reminds me of the procedure I would use on my race motorcycles to achieve solid braking with more feel.

I would pull in the master cylinder lever with a velcro strap so there was maximum pressure on the whole system.

In about four hours all of the microbubbles in the system would rise to the radial master cylinder where a quick mini bleed would clear the system.
 
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On mtn bikes that used certain hydraulic fluids in the brakes, I would get better performance from degassing the fluid under vacuum as shown here. I would degas in the syringe until no large bubbles would form and gather. When reading any of the issues people are having, my first thought is vacuum pump... good demo here!

this was a little known trick in the bike world (long time hobby and former mechanic in the nineties) for brakes that eluded easy set up.
That’s why I always leaned more to SRAM brakes over Shimano since the latter uses mineral and gravity (for the most part) while SRAM pulls and pushes fluid from lever to caliper with syringes.
 

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