Bench testing globes?

[Badlarry]

Good evening, my fiancee and I have our 03 LX at the local Lexus Indy for a shave and a haircut. They did a rear AC delete, a new exhaust, and they installed 4 new globes which I provided. I went the frugal route (I know-I know) and bought 4 off brand from an ebay seller (good reviews). I’ll attach the report from after they installed them but basically they’re telling me that they believe the precharge in the globes isnt where its supposed to be. I verified that they ruled out all other contributing components, pump, screen, 4 way valve, solenoids, main accumulator, height sensors, and rear springs so we’re not chasing our tail. They verified this and have narrowed it down to the globes. Question here is; can the globes be bench tested for what should be the proper precharge? They’re saying that they cant get the PSIs/Mpa-g where they’re supposed to be. I know just enough about this system to be dangerous but by no means an expert. Thanks in advance.

 

[LXfromTX]

No surprise that Chinese knock-offs would be a bust. They have flooded the market of NEW replacement parts with absolute crap. Ask automotive shops about BAD NEW PARTS and knock-offs and you'll hear all about it.

 

[Badlarry]

No surprise that Chinese knock-offs would be a bust. They have flooded the market of NEW replacement parts with absolute crap. Ask automotive shops about BAD NEW PARTS and knock-offs and you'll hear all about it.

I’m doing a real good job of kicking my own ass, thanks..

 

[Rhetoric]

The pressures they listed have nothing to do with the accumulator health. Those pressures tell you how much the AHC is compensating for physical springs.

You need to adjust your torsion bars for front pressure and replace rear springs for rear pressure.

Check the graduations of the fluid in the reservoir when you do a H - N - L height change. New globes should have over 10 graduations (up to 14 I believe). This info is clearly mentioned in the FSM.

 

[uHu]

As Rhetoric said.
The AHC pressure will be the same, whatever the precharge pressure in the globes. There is no connection between the two at all.
What decides the ahc pressure is:
- weight of vehicle (how much there is to lift)
- state and adjustment of steel springs (how much help will the ahc get)
- lifting height (ride height - the higher, the less help from steel springs)
Whether the gas springs' (globes') membranes are fully compressed (bottomed out) or not at all, or blanked off, doesn't change any of those three factors.

The globe health, as measured by the difference in fluid between High and Low, can be measured according to the FSM procedure (counting notches on the reservoir) only when the three factors are in spec:
- Weight
- Ride hight
- AHC pressure

What will be affected by a wrong globe precharge, is damping and suspension travel (characteristic). If too low, the globe will bottom out, if too high, there will be too little fluid for the damping to be effective.

PS
It looks like the garage either don't know what they are doing, or they just want to sell you new, expensive globes.

 

[Badlarry]

The pressures they listed have nothing to do with the accumulator health. Those pressures tell you how much the AHC is compensating for physical springs.

You need to adjust your torsion bars for front pressure and replace rear springs for rear pressure.

Check the graduations of the fluid in the reservoir when you do a H - N - L height change. New globes should have over 10 graduations (up to 14 I believe). This info is clearly mentioned in

As I said, I’m not an AHC expert myself by any means but I am an engineer and my reading comprehension is decent. I am
aware that the PSIs they listed are not directly related to a number the globe produces but instead a relationship of components.
From what I understand the tech has already made torsion bar adjustments and was unable to get the MPa-g #s where they need to be. Honestly, when the service advisor called and we spoke about the condition my 1st concern about their theory was they didnt adjust the torsion bars enough but I was assured that they had. I verified that they tested the pump, checked the screen, tested the solenoids on the 4 way valve, verified the main accumulator is performing as it should as well as the height sensors. They also said the rear springs are fine, good enough to get the #s where they need to be. So, going by what they said I was curious if the globes could be bench tested, but I suppose that the test procedures while their installed tell the same thing. How would the tech have deduced that the precharge in the new globes was insufficient as opposed to the torsion bars being roached?

 

[Badlarry]

As Rhetoric said.
The AHC pressure will be the same, whatever the precharge pressure in the globes. There is no connection between the two at all.
What decides the ahc pressure is:
- weight of vehicle (how much there is to lift)
- state and adjustment of steel springs (how much help will the ahc get)
- lifting height (ride height - the higher, the less help from steel springs)
Whether the gas springs' (globes') membranes are fully compressed (bottomed out) or not at all, or blanked off, doesn't change any of those three factors.

The globe health, as measured by the difference in fluid between High and Low, can only be measured according to the FSM procedure (counting notches on the reservoir) when the three factors are in spec:
- Weight
- Ride hight
- AHC pressure

What will be affected by a wrong globe precharge, is damping and suspension travel (characteristic). If too low, the globe will bottom out, if too high, there will be too little fluid for the damping to be effective.

PS
It looks like the garage either don't know what they are doing, or they just want to sell you new, expensive globes.

I honestly think they dont know the system well enough. They are decent people, no high psi sales tactics. Pretty much put the ball in my court and asked what I wanted to do. I said whatever it is, I DO NOT want to throw parts at it w/out being 100% certain we’re saying that the new “knock off” globes are the problem.

 

[uHu]

...From what I understand the tech has already made torsion bar adjustments and was unable to get the MPa-g #s where they need to be. ...

That means he hasn't turned the adjuster far enough, or hasn't re-indexed the bars(s) to "gain more adjustment".

... They also said the rear springs are fine, good enough to get the #s where they need to be. ...

According to the rear pressure reading, they are obviously not OK; if the height and weight numbers are at spec. Generally, if the coil springs are 5 years old, the ahc pressure will get higher than spec.

 

[BullElk]

I may have missed this but did you or are you driving your LX with the new globes? If so, how does it ride? How does each corner individually respond to road resistance?

 

[Badlarry]

That means he hasn't turned the adjuster far enough, or hasn't re-indexed the bars(s) to "gain more adjustment".

According to the rear pressure reading, they are obviously not OK; if the height and weight numbers are at spec. Generally, if the coil springs are 5 years old, the ahc pressure will get higher than spec.

Hhmm, If I was a betting man I’d say he ran out of adjustment and didnt reindex them. Good catch. I personally was unaware that reindexing them might be the answer.

 

[Badlarry]

I may have missed this but did you or are you driving your LX with the new globes? If so, how does it ride? How does each corner individually respond to road resistance?

Its still at the shop. Suspension isnt repaired yet.

 

[Rhetoric]

Oh good. An engineer. Thank you for sharing your credentials, Larry.

This forum is full of great information. Keep reading.

I would never expect Lexus to know what to do with these trucks, let alone an AHC system. Lexus wants bread and butter RX oil change work, not repairs on a platform designed on Windows 95 computers.

 

[Badlarry]

Oh good. An engineer. Thank you for sharing your credentials, Larry.

This forum is full of great information. Keep reading.

I would never expect Lexus to know what to do with these trucks, let alone an AHC system. Lexus wants bread and butter RX oil change work, not repairs on a platform designed on Windows 95 computers.

Ugh, It seems as though the AHC escaped many a tech; testimonial to how well they were made.

 

[uHu]

BTW, if you are getting new rear coils, consider getting something stiffer than the standard Lexus Pink.
Here are some part ##, stolen from another thread in here:
48231-6A750 W(ACTIVE HEIGHT CONTROL); H=455, PINK PAINTED
48231-6A770 W(ACTIVE HEIGHT CONTROL); H=485, PURPLE PAINTED
48231-6A780 W(ACTIVE HEIGHT CONTROL); H=500, BROWN PAINTED
Maybe get the Purple if normally driving empty, and the Brown if you normally carry something in the rear.

 

[Badlarry]

BTW, if you are getting new rear coils, consider getting something stiffer than the standard Lexus Pink.
Here are some part ##, stolen from another thread in here:
48231-6A750 W(ACTIVE HEIGHT CONTROL); H=455, PINK PAINTED
48231-6A770 W(ACTIVE HEIGHT CONTROL); H=485, PURPLE PAINTED
48231-6A780 W(ACTIVE HEIGHT CONTROL); H=500, BROWN PAINTED
Maybe get the Purple if normally driving empty, and the Brown if you normally carry something in the rear.

Much appreciated.

 

[Badlarry]

@PADDO could you make any educated theories based on what has been discussed thus far?

 

[ndg]

As everyone above has said the accumulators have no affect on the system pressures of a static vehicle. Either the springs are soft/out of adjustment, there's additional weight in the vehicle that needs to be compensated for, it's had a sensor lift in the past or something is physically stopping it from lifting (unlikely).

However to answer your initial question - yes you can bench test globes. But with the caveat that I haven't seen values for stock globes so you'd have nothing to compare to if you did. Our accumulators have two key values that affect performance - volume and pre-charge pressure. Citroen globes also have the suspension damping elements built in to the globe, but the TLC has that in the valve block.

To bench test you would need a pressure pump and gauge - I've used an enerpac to do this on a work project in the past. You use the enerpac to gradually build pressure recording for each pump of the handle. the slope will start out very steep (lots of Bar/pump) and then suddenly flatten out. The inflection point between these two lines is the knee point and tells you what the pre-charge pressure is. It's essentially the point at which the diaphragm begins to move. The initial ramp in an idealised system would be vertical as there would be no entrained air or compliant hoses involved, but it's never perfect.

The volume could be checked by measuring the flow into the accumulator between the knee point and saturation. Saturation is when the diaphragm bottoms out at max pressure and is characterised by the slope suddenly increasing again. I have no idea how high this pressure is - it will be substantial! You could also measure coming down in pressure by finding the knee and saturation pressures and then measuring the volume of fluid released to drop between these two numbers.

The plot below is an indication of the shape of plot you would expect to get - NB it is not measured data and I've picked random numbers! In the plot below the pre-charge would be 10 Bar.

I'm pretty sure this is the work Peleides in the UK will have done to create their aftermarket option which I generally hear good things about. Have the rest aof the aftermarket done the same though? It's possible they have acquired a copy of the original drawing which would have specified pre-charge, but if they have changed the volume the tune (spring rate) of the accumulator will be wrong.

 

[uHu]

The accumulators' (globes, spheres) charge pressure is specified in the FSM.
Fronts: 2.26 MPa
Rears: 2.65 MPa

 

[Badlarry]

As everyone above has said the accumulators have no affect on the system pressures of a static vehicle. Either the springs are soft/out of adjustment, there's additional weight in the vehicle that needs to be compensated for, it's had a sensor lift in the past or something is physically stopping it from lifting (unlikely).

However to answer your initial question - yes you can bench test globes. But with the caveat that I haven't seen values for stock globes so you'd have nothing to compare to if you did. Our accumulators have two key values that affect performance - volume and pre-charge pressure. Citroen globes also have the suspension damping elements built in to the globe, but the TLC has that in the valve block.

To bench test you would need a pressure pump and gauge - I've used an enerpac to do this on a work project in the past. You use the enerpac to gradually build pressure recording for each pump of the handle. the slope will start out very steep (lots of Bar/pump) and then suddenly flatten out. The inflection point between these two lines is the knee point and tells you what the pre-charge pressure is. It's essentially the point at which the diaphragm begins to move. The initial ramp in an idealised system would be vertical as there would be no entrained air or compliant hoses involved, but it's never perfect.

The volume could be checked by measuring the flow into the accumulator between the knee point and saturation. Saturation is when the diaphragm bottoms out at max pressure and is characterised by the slope suddenly increasing again. I have no idea how high this pressure is - it will be substantial! You could also measure coming down in pressure by finding the knee and saturation pressures and then measuring the volume of fluid released to drop between these two numbers.

The plot below is an indication of the shape of plot you would expect to get - NB it is not measured data and I've picked random numbers! In the plot below the pre-charge would be 10 Bar.

View attachment 4019752

I'm pretty sure this is the work Peleides in the UK will have done to create their aftermarket option which I generally hear good things about. Have the rest aof the

As everyone above has said the accumulators have no affect on the system pressures of a static vehicle. Either the springs are soft/out of adjustment, there's additional weight in the vehicle that needs to be compensated for, it's had a sensor lift in the past or something is physically stopping it from lifting (unlikely).

However to answer your initial question - yes you can bench test globes. But with the caveat that I haven't seen values for stock globes so you'd have nothing to compare to if you did. Our accumulators have two key values that affect performance - volume and pre-charge pressure. Citroen globes also have the suspension damping elements built in to the globe, but the TLC has that in the valve block.

To bench test you would need a pressure pump and gauge - I've used an enerpac to do this on a work project in the past. You use the enerpac to gradually build pressure recording for each pump of the handle. the slope will start out very steep (lots of Bar/pump) and then suddenly flatten out. The inflection point between these two lines is the knee point and tells you what the pre-charge pressure is. It's essentially the point at which the diaphragm begins to move. The initial ramp in an idealised system would be vertical as there would be no entrained air or compliant hoses involved, but it's never perfect.

The volume could be checked by measuring the flow into the accumulator between the knee point and saturation. Saturation is when the diaphragm bottoms out at max pressure and is characterised by the slope suddenly increasing again. I have no idea how high this pressure is - it will be substantial! You could also measure coming down in pressure by finding the knee and saturation pressures and then measuring the volume of fluid released to drop between these two numbers.

The plot below is an indication of the shape of plot you would expect to get - NB it is not measured data and I've picked random numbers! In the plot below the pre-charge would be 10 Bar.

View attachment 4019752

I'm pretty sure this is the work Peleides in the UK will have done to create their aftermarket option which I generally hear good things about. Have the rest aof the aftermarket done the same though? It's possible they have acquired a copy of the original drawing which would have specified pre-charge, but if they have changed the volume the tune (spring rate) of the accumulator will be wrong.

Excellent write up, thank you for the tutelage. Appreciate that explanation.

“As everyone above has said the accumulators have no affect on the system pressures of a static vehicle. Either the springs are soft/out of adjustment, there's additional weight in the vehicle that needs to be compensated for, it's had a sensor lift in the past or something is physically stopping it from lifting (unlikely).”

Yeah, funny here. No weight in the vehicle, no sensor lift in the past, and nothing stopping it that I could even remotely conceive of. As mentioned before, it could be that the tech ran out of torsion bar adjustment and didnt reindex them, and then possibly defaulted to bad globes? If thats the case then it also begs the question, are the rear springs bad as well?
I’m not super psyched I’m here asking questions but I feel there is a piece of the puzzle missing.

 

[ndg]

The accumulators' (globes, spheres) charge pressure is specified in the FSM.
Fronts: 2.26 MPa
Rears: 2.65 MPa

Good info, I hadn't spotted that.

It's probably worth adding that my experience is with floating piston accumulators which will have a sharper transition with some breakaway hysteresis. The diaphragm style probably has less hysteresis but smoother transitions which may make inferring the knee point harder.