Hello All,If i understood right from the AoA hydraulics lesson and FCOM, the standpipe in system A reservoir would prevent the loss of all fluid in case of a leak in the engine driven pump system. There should be about 20% left in the tank, so the electric pump would still keep the system pressurised.However in the PMDG 737NGX, if i program the "EDP1 HYD LEAK" failure, the fluid quantity will slowly decrease to 20%, then a warning is triggerd, because the pressure in the EDP pump system is low. That is ok, but after that the amount of fluid will go back to 0%Also when on the ground with no engines running (EDP on, but it is not spinning) the same failure will also leak fluid with only the electric pump running. When i switch off the not running EDP the leakage will stop.is that correct?

Only if upon switching off the EDP an isolation valve to the EDP closes. AFAIK this only occurs when you pull the fire handle. The leak is supposed to be with the EDP itself, right?Best regards,Robin.

Yes it says the EDP and its accosiated lines. Do you suppose the fluid is lost because the system is still presurrised by the electric pump?If that is so why would it stop the when the EDP is switched off?regards Jos

If the leak is in the A engine driver pump or its lines, then the volume should stay at 20%. You could develop a leak elsewhere in the system and lose all quantity. There really isn't a checklist for hydraulic leak, itself.

It's not correctly simulated.An EDP leakage will have these results in the event of the leakage is between the reservoir line to the pressure module in the wheel well:Hyd will leak until 20%, then the low pressure comes on, no more pressure will be avaiable from the EDP, it will also run dry, and it is not a good thing., the EMDP will still works.In the schematic, you can see in yellow the EDP line, any leakage in the yellow side will be limited to the 20% of tank, this 20% is then protected from going to 0 by the check valves (cyan).Any leakage over that valves will produce 0% of hyd fluid and it is no more an EDP leakage as you are far from it.

Thanks for your help. I assumed that because the title of the failure is "EDP1 HYD LEAK" that the leakage would be in the yellow part of your schematic.

So i expected 20% remaining fluid.

 

regards Jos

Yes, and that is what is called EDP leakage, a leakage on the EDP oil circuit.

It is wrongly simulated, but, as it is a complex simulation, it is difficult to reproduce all things.

Hello all,

 

but in an case off a pressure lost we got hydraulic fuses as well! If the amount of flow through that fuse is to high it will close immediately.

If I'm wrong than sorry, but I don't think if all the systems have a back up they will alloud that the associated system will dry out,or?

 

Regards,

 

Sven Wendel

Fuses are installed on some parts of the systems to prevent a total hyd loss, but, as you can see from the drawing, there is no fuse installed in the EDP and EMDP circuits. If a leakage is present in one of them, the tank will be emptied until it reaches the level of the supply tubes (20% in case of EDP, 0% in case of EMDP)

Fuses are installed on systems like brakes, landing gears, slats, reverse. Not in the supply system.

The 737 is also supposed to fly with a total hydraulic failure, so there is non need for an extra safety.

The Standby system uses also fuses for the slats.

The standby system is protected from the main system leakage by its own reservoir (filled by the B system).