[Richard]

As long as the tank is vertical gravity will ensure the N2 is not entrained into the oil. We can get into some really esoteric discussion about the solubility of N2 in ATF but thats not what you are talking about

[hypoxia]

Richard, It's vertical in that the fluid is at the top and the N2 is at the bottom.  The photos are looking up at it.  Is that what you meant?         

[Richard]

Oh my !!!!!!! That is bassackwards. The fluid should be at the bottom.

In theory it shouldn’t make any difference, but with the accumulator mounted upside down, a failure in the bladder wreaks havoc with the system. It is going to fill the hyd line with N2.

I am sorry for being so dense. It never occurred to me that the accumulator would be put in upside down.

[hypoxia]

If you boys are going in the business of fixing your ZF systems and you don’t want to hand pressurize

That'll certainly be a consideration if I have to flush the entire system.  I have Newell on speed dial for the morning!

[jdkskyking]

In these photos from a service manual, the system used for illustration has two accumulators. They are mounted fluid fill side up with the porting to fill the system. 

   

Richard is correct in the preferred accumulator mounting position, I read that in the HYDAC US catalog version. 

hydac-accumulators.pdf Size: 7.97 MB  Downloads: 8

Seems like a rupture in a bladder will require service no matter what. 

From your picture, the gauge set works! Intelligence on the attachment and operation would be valuable. I only have the ZF documentation/service manual for that info (most ZF info gives you just enough to leave you guessing).

[jdkskyking]

ZF Product Overview 

More ZF information. 

ZF Axle Transmission Info .pdf Size: 19 MB  Downloads: 1

ZF - Bus Axle Installation Instructions .pdf Size: 7.8 MB  Downloads: 1

OPERATING INSTRUCTIONS?INDEPENDENT WHEEL SUSPENSION?RL 85 : RL 85 E : RL 85 EC?FRONT AXLE:TAG AXLE RL 85 A.pdf Size: 1.05 MB  Downloads: 1

Highlighted - ZF Servocom:Gearbox .pdf Size: 904.94 KB  Downloads: 2

Might be redundant info in this thread. I’m sifting through my years of research. 
JK

[hypoxia]

I just read the accumulator testing procedure again for the 15th time.  I had made an assumption that fluid coming out of the N2 side of the accumulator would mean there is a ruptured diaphragm, however the N2 pressure is just below 12 bar.  The accumulator is 2 liter, if the diaphragm ruptured there would be very little pressure when the accumulator filled with fluid.  I think the entire RAS is around 6 liters of hydraulic fluid.  That is why the MCI manual says "If the pressure reading is less than 20psi, replace the accumulator."  When testing the accumulator, Newell says it is normal to have some fluid come out. I was told to charge the hydraulic side to 250 PSI.
   

[jdkskyking]

I just read the accumulator testing procedure again for the 15th time.  I had made an assumption that fluid coming out of the N2 side of the accumulator would mean there is a ruptured diaphragm, however the N2 pressure meets specs at just below 12 bar.  The accumulator is 2 liter, if the diaphragm ruptured there would be very little pressure when the accumulator filled with fluid.  I think the entire RAS is around 6 liters of hydraulic fluid.  That is why the manual says "If the pressure reading is less than 20psi, replace the accumulator."  I can't wait to hear the explanation of where the fluid came from when testing the accumulator.

 If you place a pressure gauge on the hydraulic block, what is your “hydraulic pressure”?

               
   

[Richard]

The only way to test the integrity and pressure of the bladder is to relieve the pressure on the hydraulic side.

Here’s why. The system is closed, assuming no leaks in the RAS hydraulic lines or cylinders. It was initially pressurized to some level, say 225 psi, which compressed the N2 in the bladder to 225 psi. Now if the bladder ruptures, again assuming no leaks in the system, the pressure will STILL be 225 psi.

To make the situation way more interesting, with the accumulator mounted upside down, the N2 has now traveled to the high point in the system. But it’s still there, and the pressure will still read 225.

All that has happened if the bladder ruptured is the hyd fluid and N2 did what gravity told them to do.

If this is the case you must be very very careful if breaking into the hyd system. Normally in an all hydraulic situation, as soon as you crack a fitting the pressure relieves due to the incompressibility of the fluid. But now we have a bubble of compressed gas that will expand and produce pressure until the pressure reaches 1 bar or 14.7 psi.

I commend both of you for digging in and trying to test and figure this out. I know NOTHING about the ZF system, my commentary is based upon working with hydraulic systems in industrial environments. So yo have to take my input with a boulder of salt, not a grain.

[jdkskyking]

That’s why I ask if he can place a gauge on the left outboard minimess connect and see what the hydraulic pressure is.

IF you want to drain the pressure you will need a line connected to one of the minimess connectors and a valve connected to the other end of the line and preferably terminating in a container.