A340 HYD SYS, RAT MAN ON logic

[Microburst2002]

RAT MAN ON pushbutton
The flight crew may extend the RAT at any time by pressing the RAT MAN ON pb.
Note: The RAT automatically extends, if:
‐ AC NORM buses, and Engines 1 and 4 fail, or
‐ Four engines fail, or
‐ GREEN + BLUE LO LVL + engine burst is detected, or
‐ Four engine-driven pumps' low pressure.

What's the use in the RAT if there is LO LVL in the green sys?
Is there an auxiliary reservoir or something?

[bvcu]

Effectively yes, a standpipe for normal use and bottom of tank for emergency, forget details as course done in 98 !!!

[Microburst2002]

That is what I thought. The same as in a 757 or many other models, however this bottom-of-the-reservoir way of protecting against a leak needs piping of its own to and from the users, right? and these users are typically few and emergency related, such as alternate brakes or similar.

I mean, it cannot just keep serving all the users. The fluid would go out through "the hole" in no time, right?

Definitely there is very little information about this in the FCOM, and I don't have the AMM...

[spannersatcx]

hydraulic fuses protect the system.

[Microburst2002]

I was confusing the fuses with the priority valves, for a while, hence the edit.

As I understand, a fuss will shut its line when it detects a leak due to to the flow it produces, right?

But if the system goes LO LVL, this means that the fuse hasn't been able to isolate the leak, or maybe the leak ocurred well upsteam of any fuse. In ant case, the fluid is just gone. How can you power a hydraulic system with a RAT if there is no fluid?

FCOM is not very clarifying regarding this

[Microburst2002]

Time to bring back this issue!

I still can't understand what happens here.

If there is a GREEN LO LVL, according to the FCOM the shut off valves will close automatically. If there is another system affected by a LO LVL (blue or yellow), then they remain closed, automatically. According to the FCOM this is done in order to allow the RAT to restore the green system.

So it seems obvious that there is an alternate piping that bypasses the shut off valves and goes to the users, but Why is it that they don't show it to us? Where is the use in showing us the priority valves, for example, and not the way the RAT can restore the whole green system with just 8 ltrs remaining in the reservoir? And Why shutting off the valves? Is it because the design assumes that the leak occurs somewhere between those valves and the point at which the alternate piping merges with the normal one?

In the sim, when the TRI gives you dual low level and the RAT deploys, What happens? Is the system recovered?

Any "freaky" here can provide us with a schematic of the system from the AMM?

thanks!