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to member DELCOM

Started by luxair_ca, Tue, 1 Sep 2009 17:41


Those birds powered by PW4000 series engines require some more fluid in order to fill up additional lines and equipment in order to power the thrust reversers. 24 actuators take care of that, 3 on each reverser half, so 6 on each engine. The volume necessary to fill up these additional lines for the PW unique system is unknown (at this point) to me, what I know is that deploying a pair of reversers (meaning 6 actuators) on one engine will draw 0.247 us gallons out of its respective reservoir. Enough to drop QTY reading on the EICAS HYD page.

And here comes the interesting called exchange volumes. One can understand that operating certain flight controls, moving gears up and down, etc will change the fluid level in the reservoirs which is immediately sensed be the four HYD QTY transmitters and displayed in real time on the EICAS. Hydraulic systems are serviced to the green band (0.80 to 1.10) with the a/c in a certain configuration. Some airlines might want 1.00.

All gears down, gear doors closed.
Nose and body gear steering in neutral.
Spoilers retracted.
Thrust reversers stowed (PW4000 only).
Parking brake accumulator nitrogen precharge set.
All three (one for each WLG, and one for both BLG's) surge accumulators nitrogen precharge set.
Parking brake released.
Hydraulic reservoir pressurization system is pressurized (preferably being pressurized) with the pneumatic system.

Balanced actuators and rotary actuators have no effect on exchange volumes. You can operate INBD AILERONS, OUTBD AILERONS, UPPER RUDDER, LOWER RUDDER, INBD ELEVATORS, OUTBD ELEVATORS, INBD T/E FLAPS, OUTBD T/E FLAPS will not change HYD QTY value on the EICAS HYD page. The design of these linear actuators sport equal volume on both sides of the piston. It is achieved by the actuator rod extending through the cylinder on both sides of the piston. The amount of fluid pressed in on one side of the cylinder equals the amount squeezed out from the other side. Rotary actuators for the T/E FLAPS are like a rapid flowing down the hillside rotating a wheel for the blacksmith workshop. Clearly no volume change here.
Unlike the unbalanced linear actuators. They have different volumes on each side of the piston. Rod is only on one side of the piston, creating "smaller space". Retracting one of these actuators will require less fluid than extending it. The difference in volume equals rod diameter area times stroke. Opening body gear doors, retracting BLG will increase QTY reading for SYS 1.
SYS 2 has no equipment capable of increasing the level of the reservoir. Of course spoilers 2, 3, 10 and 11 will put  fluid back in the reservoir upon retraction, but first you had to extend them. That's back to square one. Normal position for a spoiler is down.
SYS 3 has nothing to add to reservoir level increase, like SYS 2...they only take (dropping fluid level).
SYS 4, Rudder ratio changer and opening WLG doors will increase QTY.

Next...most of the consumers will cause a drop in reservoir fluid level. Which ones and how much? Anyone interested?

Please someone stop me, if it's getting boring.


Hardy Heinlin

Quote from: delcomNext...most of the consumers will cause a drop in reservoir fluid level. Which ones and how much? Anyone interested?

Yes :-)

Thank you, Delcom!



This is very interesting delcon.

It seems that if hydraulic systems 1 and 4 will show quantity of 1.0 on the ground, after departure and gear up (if we ignore everything else), system 1 (body) should display more than 1.0 (because to retract the gear you retract its actuator) and system 4 (wing) should display less than 1.0 (because to retract the gear you extend its actuator).

Edit: I forgot for a second the nose gear. Like system 4 the actuator (pressurized by system 1 of course) extends (and not retract as the body actuators do) to retract the nose gear but sine the body actuators are bigger (and there are 2 of them), the result (more fluid in the reservoir after gear retraction) is the same.

I have an El-Al (which has PW engines) training manual for the hydraulic system and the Hydraulic Fluid Quantity table shows the very same numbers you gave (like no extra fluid is needed for the thrust reversers) but it could be a mistake.
Avi Adin


Nice one Avi,

I've just constructed some graphs on which I plotted the amount of fluid pressed back in the reservoir against different phases of NLG and BLG retraction. The phases are simply: open doors, retract gears, close doors. I have info on volumes describing rod end displacements for linear actuators in the landing gear system. Putting them in a simple formula resulted in 0.64 liter additional fluid in SYS 1 reservoir after retraction.

1. When the doors open...the two BLG door actuators add, NLG door actuator takes fluid from the reservoir. Total is 0.90 liter rise.
2. Gears went up...BLG actuators added, NLG actuator drew fluid. In total 0.64 liter rise. At this point we have (0.9+0.64) a liter and a half more fluid in the reservoir, but we still have to close the doors.
3. Opposite of point 1, so 0.90 liter drop.

One can spot it immediately...once you have the gears up and press the nose-body alternate P/B, you'll be missing the doors close phase, leaving more fluid in the reservoir.  

The rest of the components are incorporated in the formula as well such as 2 uplock actuators, 2 downlock actuators, and the NLG lock actuator. Sequence valves do not change volumes. This is for Qavion only->->->Wheel despin actuation volume(s) are excluded here. ;)

Projecting these volume numbers to EICAS QTY readings is again a different story. The linear quantity transmitter measures fluid level height in a rather odd shaped vessel. We cannot simply state that adding let's say 1 gallon will rise EICAS reading by 0.1 percent. Unfortunately it's non-linear due to the shape and components inside the vessel. With the help of some known volume/EICAS value sets, I've created a curve, so now I can translate all those gallons pumped in and out the reservoir pretty accurately to EICAS units. This graph of mine only applies to the outboard reservoirs (1&4), the inboard ones (2&3) are different in shape (volume, transmitter) so they call for an other curve.

I'm not sure where we are exactly going with this airplane "porn", but hopefully Hardy finds some usable info in it.  :)

PS: Hardy, back to your question. How long does it take to pressurize let's say sys 1 with an ADP? I have no clue, Lol. I've never measured it. You've guessed 1 to 2 seconds. You might be right, but I'd say 3 to 6 sec. Now I just closed my eyes and tried to recall the procedure. Same problem with the EDP's and ACMP's...just cannot tell. In a few days (hopefully) we'll have a healthy bird, I'll do my best to take accurate measurements.



Hi delcom,

Regarding your last paragraph you / we should remember that there is a time delay for the operation of the ACMP demand pumps when the switch is set to ON or AUTO: 1.5 sec for sys 2 and 3.0 sec for sys 3 (this to prevent the 2 AC motors start together).
This can also explain the relative long time of pressurization.
Avi Adin


Indeed Avi,
as long as the inboard systems are equipped with ACMP's, there will be time delays and in addition it's different times as you described. You don't wanna start up two electric motors simultaneously, each drawing 167 Amps at start up. However the system logic won't prevent you to start SYS 3 at T minus 1.5 sec. You wouldn't do that deliberately, would you. ;)      


Interesting airline option...C level advisory messages:

Hydraulic quantity at or below 0.50, inhibited by HYD QTY LOW X.



Surprise for Q,

sorry for the low quality shot, it's just a frame I grabbed out of an even lower quality mobile phone "video" of mine.



Jeroen Hoppenbrouwers

Quote from: delcomYou don't wanna start up two electric motors simultaneously, each drawing 167 Amps at start up. However the system logic won't prevent you to start SYS 3 at T minus 1.5 sec. You wouldn't do that deliberately, would you. ;)      
I saw Hardy scribbling something on his hand when he read this.


"Airplane porn," LOL.  When it comes to 747 engineers/mechanics, are some guys just hydraulics guys, and others electrical guys, or does everyone do everything?
Will /Chicago /USA


Ok Hardy,
last night we made some noise after installing a new ADP on SYS 1. Here are my test results.
Zero seconds...SYS 1 demand pump selector is rotated to ON. Amber circle replaced by white circle, OFF removed. (to my surprise SYS 1 AUX OFF label is removed as well) Press 100 PSI.
1.5 flow line is drawn. DEM circle shows white valve in the open position, OFF label reappears in the white AUX pump circle. Press 2550 PSI at this point.
2.8 sec pressure stabilizes around 3000 psi.
Things happened so fast that the 2550 value was still represented in amber color, which is against the 1300 OFF 1200 PSI + 2 sec rule. I couldn't follow the SYS FAULT and PRESS lights on the overhead, since I had my camera aimed on the INBD CRT.



SYS 1 depressurization times and pressures.
0 sec...3000 PSI
1 sec 2960 PSI
2 sec 2830 PSI
3 sec 2710 PSI
4 sec 2440 PSI
5 sec 2290
9....2220 1220
10 sec 1140 PSI still white!!! HYDIM 1 started timer passing 2000 PSI. Any fluctuations reaching 2000 will reset this timer.  
1030 amber
28 sec 500 PSI
40 sec 300
65 sec...100 PSI

No flight controls were moved, no one was playing with the brakes etc.


Hardy Heinlin

That's great. Thank you, Delcom.




Wow...9 sec is obviously 1220 PSI (not I typed incorrectly).