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Guest schimmi

Hydraulic failures not simulated?

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Hi!I am trying to make the engine hydraulic pumps fail. I have running engines on the ground, electric pumps for A and B are off, engine pumps are both switched on. I have proper 2800psi preasure on both systems. Now I activate the failure for the engine pump B in PMDG menu. After 60 seconds they become active (I have checked that in the failure dialog). But the preasure keeps the same. Only when I switch the engine pump B to off the preasure decreases. Are the failures simulated at all?Thanks in advance Schimmi

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"Only when I switch the engine pump B to off the preasure decreases. Are the failures simulated at all?"The 737NG has two back-up hydraulic systems, Schimmi.1. The Alternate System: This uses a separate hydraulic reservoir and a back-up electric pump. This system can be automatic activated if the conditions are right. This pump powers leading edge flaps and slats, both engine reversers and the Standby Rudder system.2. The PTU: Automatic system. It uses the (good) pressure in system A to run a pump which powers the leading edge flaps and slats (systems usually powered by system :(.However, I assume you are looking at the pressure indications on the Upper IDU (LCD display) to determine whether you have pressure or not? All we need to find out now is at what point the hydraulic pressure is being sensed. If the pressure is sensed prior to the Alt System and PTU "plumbing", then you should see a system pressure loss on the Upper IDU. If the pressure is sensed further down the line (after the Alt & PTU systems), then you may not see a pressure loss.Looking at my books, I am unable to determine at what point the pressure is sensed in relation to the back-up systems. It would make sense to me to show low pressure when the main pumps have failed... as not all the hydraulic-powered airplane systems are powered by the back-up systems... but the NG really is strange beast ;-) I'll hand this one over to the experts :-)Cheers.Ian.

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I have found the following figure about the hydraulic system of the B737: http://www.b737.org.uk/schemehyd.gifI don't know whether the NG uses exactly the same.If I interpret the figure correctly the pressure is measured directly below the point where the elec1 and eng2 pumps' circuits come together. There is no direct connection to the standby system. The PTU only connects the slats to the standby system. It can't keep up the pressure of the B system completely. Without eng2 and elec1 the pressure is supposed to drop.Can anybody comment about this for the NG?Schimmi

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I (finally) found a diagram for the NG which looks similar to the one in your message, Schimmi. I'd say you are probably right about there being an anomaly in there somewhere. Perhaps PMDG can look into this? (Either the indication logic is incorrect or the hydraulic fault simulation is not operating in the way we think it should?).Cheers.Ian.

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