Hydraulic depressurization

[marcom]

Hi everyone!A quick question to the engineers/pilots on this forum:How fast does a hydraulic system depressurize, after all hyd. pumps have been switched off and there are no users activated (ie at the gate, at shutdown)IMHO PIC looses its pressure way too fast, especially if compared to PS1.3. Can someone give a ballpoint figure?Also, what pressure is required for some (sluggish) movement of the flight controls? 3000 PSI is normal, but what about 1500 or 1000 PSI?Thanks for the answers,Regards,Mark

[Guest Ian_Riddell]

"IMHO PIC looses its pressure way too fast, especially if compared to PS1.3. Can someone give a ballpoint figure?"I haven't checked PS1.3's pressures with no load (recently), Mark, but I do recall they drop way too slowly than they should with loads applied (on the ground, with no windmilling engines). I have mentioned this to Hardy in the dim, dark past. Hopefully, when/if PS5 comes out, this will be rectified.Anyway, I'll try and check them tomorrow on a real aircraft as per your specifications (I should be able to test at least one of these aircraft).Cheers.Ian.

[marcom]

"I should be able to test at least one of these aircraft"Ian, you have an awesome job! And you get paid for it aswell! :-)Thanks!Regards,Mark

[Guest Ian_Riddell]

Hi, Mark.I was only able to check out two pumps (on a 767) this evening.Before I switched on the pumps, the pressures were 50, 60 and zero psi (L, C & R systems respectively).I switched on the Left Demand Pump and the pressure went from 50 to 3000 or so psi. I then switched off the pump and started the stopwatch. Within 15 seconds, the pressure had dropped to one hundred psi and within 25secs it had dropped back to its starting pressure of 50 psi. I then switched on the Right Demand Pump and the pressure rose from zero psi to over 3000psi. I then switched off the pump. Within 2 to 3 seconds, the pressure had dropped to two thousand psi and within 11 seconds it had dropped back to zero psi.I'm not sure why the pressure from these pumps dropped at different rates or why the pressure remained above zero on two of the pumps (I looked at the unpressurized values on another 767 and they were zero, 70 and 60. Perhaps the sensor accuracy is not all that good?).The values do drop a little faster in PIC than in real life (5 seconds or so), but nothing to worry about. I'd be more concerned about PS1's values ;-) I'll be sure to check out a 744 when I go back to work in a few days time. Cheers.Ian.

[Guest wkzzo]

Not sure about the 767 Ian but on the 757's I remember that If we had the nose landing gear door de-activation pin installed the L hyd press would appear to drop slowly .The reason for this was that the L hyd press sensor line fed through the nose lndg gear valve and the installation of the pin would restrict pressure bleed off to the actual pressure switch, so it would back bleed through other lines a little more slowly.

[Guest Ian_Riddell]

Thanks for the tip, Wallace... I'll be sure to check this out. ;-)Cheers.Ian.P.S. And speaking of hydraulics.... Anyone know what this is? :-)http://www.ozemail.com.au/~iriddell/767/YYY.jpg

[Guest MB327]

Automatic transmission in a Honda Accord? ;)Whats that adjustable wrench doing there? Thought you master mechanics only used precision tools.

[Guest HPSOV]

An ADP perhaps?

[Guest Ian_Riddell]

>Whats that adjustable wrench doing there? Thought you master >mechanics only used precision tools.Ooops.... I was hoping you wouldn't notice that, Mike (Glad I hid the gaffer tape :-hah ).Actually, the wrench is quite large and a larger one is just off-screen. I suspect the average Airframe/Engine engineer wouldn't have something this large in his/her toolbox.... so would have to go with what was left in the company tool crib. Also, it was probably for a low torque application (not for holding on wings, engines, etc).>Automatic transmission in a Honda Accord? ;) More a turbo than a transmission ;-)Cheers.Ian.

[Guest Ian_Riddell]

>An ADP perhaps?Indeed it is, HP :-) (ex-OGE)Bleed air inlet on the bottom left hand corner, turbine in the middle and turbine exit on the right. Gearbox/pump assembly on the top left hand side.Not the most pleasant of things to work on. I've had two showers since, and I can still smell/taste hydraulic fluid (perhaps still in my lungs) :~PMight have to give you a harder question next time ;-)Cheers.Ian.

[Guest]

Hi IanYup theres nothing more revolting than the smell of skydroll on your clothes and hair!!Any its DAMM sore if it hits yer eyes!!!But thankfully us avionic types dont touch the stuff too often,lol.Not good for our fair hands.Stu M

[Guest Ian_Riddell]

>Not good for our fair hands.Ain't it the truth, Stu... Anything which (actually) melts the protective rubber gloves we have to wear when doing this sort of work, can't be good for you :-hah

[Guest]

Hi IanThose woulndt be the same blue protective gloves that claim to withstand Skydrol. LOLThey dont last long.Stu.PS. You a Licenced guy Ian?