ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098

ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098 - Printable Version

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RE: ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098 - Richard - 04-20-2024

Jeff, that last pic may not be a great example.

Normally equal pressures on equal discs result in no movement.

In the pic above the surface area of the disc on the left side is greater than the surface area on the right side because the diameter of the rod must be subtracted. So in the literal answer to your question about the picture the rod and piston would move as far to the right as possible if equal pressure is applied to the ports.

Reacting to post #29, there must be something else going on with ports and internal valving in the rear cylinder that is not evident.

RE: ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098 - jdkskyking - 04-20-2024

I pulled that off the internet to simply get the answer to the question and you answered it.
So, equal pressure on each side of the “center section” will result in no movement.

The next question is can the actuating rod be moved with the pressure applied to each chamber then the answer is yes because in the case of the rear cylinder, all chambers in straight forward position, are connected and have equal pressure in the system. The chambers I’m talking about are connected together. They could have their own accumulator and then we’d have two closed looped systems working to operate the Tag tires. I know… that’s getting out there but it could be a redundant system to stabilize the rear cylinder in the event the primary steering system has a pressure failure like I originally had… just saying.

Now, I don’t know this for a fact but I’ve not read anything about valving in the “anchored” side of the rear cylinder however, there is a section that has a bottom drain.

When the cylinder is centered, the valve/port can be opened and there should be minimal fluid present and no loss of pressure/fluid.

this is the section with the drain.

Troubleshooting section of manual discussing bottom drain.

We will figure this system out… ????

RE: ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098 - hypoxia - 04-20-2024

The Accumulator Charging/Testing Tool arrived, the system pressure is just under 12 bar, probably 170PSI. When I released the pressure some oil came out which means the diaphragm is ruptured. I have a tank of nitrogen if I need it but I don't have a hydraulic bleeding/filling/charging station. Any suggestions on where to find one? Possibly make one from this Harbor Freight pump?

Jeff, I'll be going through all of your data and look at your bleeding and valve suggestions. Any suggestions to make the accumulator replacement easier will be welcome. Also will need some fluid.

RE: ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098 - jdkskyking - 04-20-2024

I’ve purchased a hand pump from AMAZON. Apparently the link is no longer available. I’ll post a pic.

By removing the accumulator for replacement, there will likely be air enter the system and really needs to be bled out. That is where adding a bleed port at the accumulator connection will be beneficial!

I have not explored the needed fittings for this. I can tell you that the accumulator hydraulic side threads are M18-1.5. I believe Newell uses a metric to SAE fitting.

To re-pressurize the system a line is connected to the side port on the rear hydraulic block.

RE: ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098 - jdkskyking - 04-20-2024

RE: ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098 - jdkskyking - 04-20-2024

This is a pic of my coach being serviced at the factory.

In this case they are bleeding the entire system using an electric powered hydraulic pump generating in excess of 600 psi. They have lines connected to bleed ports on the rear hydraulic block that return fluid to a tank mounted on top of the electric hydraulic pump reservoir. If there is air in the system it will hopefully separate in the top tank.

RE: ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098 - jdkskyking - 04-20-2024

Lines attached to bleed the system.

When it’s time to pressurize the system, the return lines are removed. Then the pressure is adjusted from the hydraulic pump and when 275 psi is achieved, the pressure in valve is closed and line removed.

RE: ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098 - Richard - 04-20-2024

The beauty of the accumulator is the marriage of the compressible gas, N2, and the incompressible hydraulic fluid.

The precharge with N2 on the bladder is only a starting point.
The real charge is set when the closed hydraulic system is pressurized. In most cases that is done with a hyd pump, however in this case something like an external pump must be used to raise the pressure inside the closed system.

The magic that happens is as the bladder is compressed by the hydraulic fluid, the N2 inside the bladder increases to match the hyd pressure. Yeah yeah, you have said this about a zillion times. But, if there were no bladder, given the incompressibility of hyd fluid, then 1 ml of fluid added to a closed system could raise the pressure by a 1000 psi or more, another drop would add another 1000 psi. Now add the bladder with the compressible gas, and it takes a significant volume of additional hyd fluid to raise the pressure in system.

Why walk you through that? In designing and using the makeshift hyd charging setup, a few drops of hyd leaking will NOT have a significant impact on the pressure within the closed loop.

If I were doing this, I would install a cross below the accumulator. Obviously the vertical ports on the cross connect the accumulator and the system. On one of the other ports install a quality gauge. On the last open port install a hydraulic 1/4 turn valve. Now using the HF pump adapted to the 1/4 turn, pump up the system to the desired pressure. Close the valve, relieve the pressure at the HF pump and remove it. For grins, put a plug into the open end of the 1/4 turn as an insurance policy. If you didn’t want to use a 1/4 turn, you could use a check valve.

RE: ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098 - Richard - 04-21-2024

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

https://www.amazon.com/VEVOR-Capacity-Electric-Hydraulic-Pump/dp/B0C1B62W5J/ref=asc_df_B0C1B62W5J/?tag=hyprod-20&linkCode=df0&hvadid=652496346682&hvpos=&hvnetw=g&hvrand=17883143482129081633&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9012338&hvtargid=pla-2186913409093&psc=1&mcid=0b48f4aa348e30c4921d094089466073

RE: ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098 - hypoxia - 04-21-2024

I'm wondering about the effect of the diaphragm failure putting that compressible nitrogen in the hydraulic fluid? I have had a few times the RAS did something odd that got my attention and once or twice I didn't think the RAS steered as much as normal.