PTU (power transfer unit) description and operation
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- Опубликовано: 19 сен 2022
- PTU (power transfer unit) the infamous Barking Dog and how it works.
The aircraft has a power transfer system to transfer hydraulic power between the Green and Yellow systems. This is necessary if one of the engine pumps fails. It also makes it possible to pressurize the Green system from the Yellow system for maintenance (with the Yellow system electric pump).
The PTU is made up of a variable displacement unit coupled to a fixed displacement unit. The variable displacement unit is connected to the yellow hydraulic system. The fixed displacement unit is connected to the green hydraulic system. Displacement of the variable displacement unit is varied to maintain the required running and breakdown pressure differentials between systems. Displacement of the variable unit is controlled by means of a control which senses the system delta pressure.
The variable displacement unit is at maximum displacement during the power transfer from the Yellow to the Green system. Then it is at minimum displacement during the power transfer from the Green to the Yellow system.
The variable displacement unit includes a hydraulic servo valve and a variable cam.
The servo valve gets input from the pressure differential, which starts the PTU. It controls the displacement of the variable cam which gives the quantity of stroke.
The PTU automatically starts to operate when the pressure in one of the two hydraulic systems is approximately 500 psi more than the pressure in the other system.
YELLOW TO GREEN (motor inlet flow 119 L/min, pump outlet flow 95/min, pump pressure 2987 psi)
GREEN TO YELLOW (motor inlet flow 75L/min, pump outlet flow 55L/min, pump pressure 2987 psi)
That’s all I can fit folks. Hope you enjoyed it. Ask your questions in the comments. As always have a fantastic day🤙 
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Brilliantly explained, thanks!
happy you enjoyed it
I don't care what ppl think! This is the best sound ever on Airbus! ❤
And it lives rent free in my head 24/7 😂
I guess it's enough for you! 😅
I used to wonder. I thought maybe some system was doing a self-test upon engine startup, but I also wondered why it sometimes lasted longer on some flights than others, and why it would also “self-test” upon engine shutdown. Knowing what I know now, it just means my Airbus is happy and wagging its tail, figuratively and literally. I’d be extremely concerned if I was on an A320 that *didn’t* bark.
I always favored the sound of the electric hydraulic pumps shutting off on the CRJ’s.
I’ve been wondering for years what that sound was. I asked the cabin crew once and they had no idea what I was talking about. And now finally, after years of waiting, it’s the PTU. Thanks man!
Glad to help
LOL, I think they were just tired of answering the same question over and over. “What noise? I don’t hear any noise. By the way, here’s a pillow, perhaps you can bury your ears in it.”
PTUが作動する音が好きです😊
BTW the best video in RUclips on PTU congrats buddy fr creating such amazing content.
Thank you very much
Always wondered what that sound is exactly. Thanks for sharing!
Thanks for watching!
Once again great content. Amazing the engineering involved in an aircraft. Thoroughly enjoy how you break it all down and explain how it all works. Cheers bud!!
Thank you very much and I’m very happy you enjoyed it 👍
The C17 also has a PTU and it sounds just like the one on the A320.
I didn’t know that, thank you for the education
Buddha! Nicknamed that because the initial delivery flight from Seattle to Charleston AFB would not have been possible without a cargo compartment full of Boeing engineers on laptops keeping it flying due to all the software glitches that had yet to be worked out to meet the delivery date. It didn’t fly again for about 2-3 months while Boeing worked all the bugs out. It was big, fat, sat on the ground and everyone worshipped it. Hence the nickname, Buddha.
A dog on our flight barked back at it.
😂😅😂
I've wondered for so long what that was, thanks for the explanation
Glad I can help
Thanks for this great explanation & the precise view! 💪 Amazing Content
thank you very much
Awesome video! Thank you very much for sharing your knowledge!!
Thank you for being here. I appreciate you watching
Nice, thanks!
Was literally wondering wtf that noise was flying back from Texas. Thanks.
That explains why my A220 was barking all the way to the runway, taxiing on one engine!
A220s have the barking dog sound too?
thanks.
As someone who works on equipment, I assumed it was a hydraulic system- but i certainly appreciate the walk through!
Glad it was helpful! Thank you for being here, I appreciate you
Now thats a quality content.. Great job buddy❤
thank you so much
Excellent upload. Above all no jarring music😂.
Glad you enjoyed it 👍
Very cool!
🤙
very good man, thanks
Thank you
To me it rather sounds like sawing a piece of wood
Yes!!
More like my neighbour at night
Thank you very much!
You're welcome! Thank you for watching.
I love this sound
This sound lives rent free in my head 🤣
When I first heard this sound as a kid I got scared thinking there was something was wrong with the engine lol
Now you know. It’s just how it functions 👍
Thanks, I already listen but never seen a real pump working. Just drowning Pics , nice meet you eeal pump... 😂
Congratulations for clever video 📹.
Thanks 👍
Love hearing the PTU, and comments from those not in the know thinking it's a dog in the cargo hold🤣🤣🤣
The Airbus A320 sounds like an Electric Pallet Jack
Wait till you hear the brake fans 😅
Informative video.except...
On the 737 what he is pointing at, is not the PTU. That is the Flap Power Drive unit. If you want to see the PTU, it would be on the beam where that reservoir(standby reservoir in the video) is attached and go near the end of the beam on the other side.
You are absolutely correct. That was my fault because the video went out of sync when I did the voice over. The PTU is very small on the 737 and as you stated in the center keel beam.
👏👏👏
👍
woof woof
😅
1:20 I'm really curious as to what causes the actual "bark" noise of the pump...? Is that due to a check valve or something like that releasing? Or due to the pump itself cycling? (I've have a difficult time trying to understand how the pump physically works, there are diagrams, but I haven't been able to find a animation of it.)
It’s due to the power transfer unit trying to keep up with the pressure on the system. Remember it’s a variable displacement pump
I also wonder. I’d hypothesize that the whining comes in when fluid flow on the higher pressure side drives a shaft that pumps up the lower pressure side, and the barking must be the sound of the variable displacement doodad varying its displacement whenever the pressure differential is greater than 500 PSI. I’d guess it must vary displacement such that one side can’t go higher without the other side going lower, thereby self-regulating the mechanical advantage the high side has over the low side as required.
I don’t know though, just guessing based on my theory about how it COULD work, not how it actually does work. Now I’m curious enough to try looking it up. I want to know whether I’m close to right, or just inventing crap in my head.
OK, I’m sort of right, sort of wrong, and it’s also more complicated than I first thought. One side (the green side, I believe) is fixed displacement, the other is variable (which I’d know if I first comprehended what Stig said). The green and yellow sides are hydraulically separate but are connected by a drive shaft. Both sides can function either as a motor or a pump. Whenever there’s a differential of 500 PSI, valves open and the higher-pressure side of the unit, whichever side that is, functions as a hydraulic motor. That spins the drive shaft so that the lower-pressure side of the unit can function as a pump. The PTU’s functionality can be boosted by an electric motor, providing additional pressure to the lower side while relieving some of load the from the engine driven pump on the higher side. I’d have to guess that the whine is from the electric motor. I’m not sure the purpose of variable displacement (to adjust mechanical advantage between the sides is still my best guess) or why it’s deemed necessary on one side but not the other. Most of all, I’m still not sure what makes it bark. So that’s where I’m at.
Thanks a lot! This video really helps. Also could you advice the source of the picture on 1:00? Would like to dig into it as FCOM is of no help.
that picture comes from the Maint manuals, its not available in the FCOM, but you can also find it online.
Always wondered what the hell that was but concluded it must be normal as the cabin crew never turned a hair. 😀
It's a disrespectful little monster!
🤣🤣🤣
It's funny lol
Sounds like it’s eating itself. Do all PTU’s make this sound or is it only Airbus?
I was on a airbus and this was running continuously for about 5mins during decent, does that mean the plane was broken? Love your work!
It’s completely normal, sometimes the pumps need to compensate and this is why you hear the noise. Just because one of the engine driven pumps are not producing enough pressure. The power transfer unit will compensate.
Thanks@@StigAviation! Love your content, looking forward to the next shift video
So small, but SO LOUD!!
Especially when the gear doors are down. You can hear it from very far
Why advantage does the PTU bring? Why did Airbus make it get used on the ground while Boeing didn't?
Because Airbus has 3 independent systems and it acts as an extra redundancy system in case one engine driven pump fails. It can still provide hydraulic power to the failed system.
A variable displacement unit coupled to a fixed displaced unit.
*me, a genius:* ahhhhhhh, I see, I see 🧐
😅 you should have seen my face when I was first learning about this back 20 years ago. 🤪
The should put sound dampers around it.
Really no need for that. It’s only on for a brief moment.
@@StigAviation unless you are on Spirit and they turn off the engines on the ramp waiting for a gate. Roof roof roof
@@PrestonelmerAnd how do they reach the gate if they turn off both engines?
u said that each fluids do not go over each other, but how is it possible to supply another hydraulic without transferring the fluid to one another?
Variable displacement pump. It just transfers the pressure not the fluid.
To clarify a little, because I did some research after having the same question as you, there are two sides of the unit (green and yellow) that are hydraulically separate, but connected by a drive shaft. Each side of the PTU can be thought of as both a hydraulic motor and a hydraulic pump. If the green side has low pressure, the yellow side functions as a hydraulic motor, which spins the drive shaft, which drives the green side to function as a pump. If the yellow side has low pressure, it’s the same idea, mirrored; the green side functions as the motor, the yellow side as the pump.
can you describe what the switch indication says when its off vs on. Im unsure how the airbus overhead push botton switches indicate on/off
Would you please be specific in what switch you are speaking about
This was in reference about the Airbus pushbutton switches on the overhead panel when turning the PTU on and off. When pressed an "off" indication. Does that mean it's off or it needs to be pushed again to actually be off.
@@absters33 this is a great question, what you were referring to is actually the whole concept of dark flight deck, so what that means is, if the unit is off, the light will come on. This will illuminate and give notification and will be very visually apparent. Since we’re working off of a dark flight, deck concept, if all lights are Off that means everything is working properly. I hope that makes sense. But it is a very comical thing when your first encountering it. Turn off, push button off Legend comes on. 🤣🤣
@@StigAviation thank you for explaining it in great detail and what indication is to be expected in normal operations. Very knowledgeable and helpful thanks!
Hi sir i am come india to kuwait PTU sound noise is come
Who let the PTU´s out? :D
lol
If there are three independent systems but only one PTU, are they really independent? If PTU fails what happens?
You just answered your own question tho. If all three systems are independent and the PTU is the cross connecting them. Even if you have the PTU fail you still have the independent systems working. You can even have 2 systems fail and still have control.
@@StigAviation I should have been clearer, if all 3 systems are connected to the PTU and it catastrophically fails (ruptures) could the pressure/fluid be lost in the aircraft or are there redundant valves that would close off.
@@user-uo3jy5vl7p all 3 systems are not connected to the PTU. Only green and yellow. But they are still independent and don’t intermix.
it makes all sense now but there is still fog for me about how PTU make this noise.
When you have a variable displacement pump, it’s constantly trying to keep up with the pressure so hence you hear the continuous noise with pitching up and down in tone and you get that bark sound.
Bro kindly make a video on 737 hydraulic system & compare it with A320 it will be an comparison of both technologies.
Like how 737 hydraulics get pressurized in case of one engine stop or start etc..
I will definitely work on that video.
Oppenheimer drums
What?😅
27 .8.2023
PTU is exactly why I cannot stand the Airbus a320 family. I have no problem with airplanes and their hydraulic noises but the A320 family's noises are extremely irritating. I love Airbus for its a350s and a380s but I try to avoid the a320s altogether (and yes, this includes the a321).
It’s not like the hydraulic system is constantly functioning, you’re not hearing that sound all the time, it’s only in the beginning and the end of the flight
@StigAviation the sound is still irritating though.
Do you think that’s annoying, wait till you hear what the brake fan sound like 🤣🤣🤣
Silly noisy European plane.
737 Max: silly crashing American plane
@@JustRememberWhoYoureWorkingFor don't forget the GTF engines that only last 5000 hours on wing, not 100,000 hours.
Pff, flown last week in a 16 year old a320 and an 8 year old 737-800 - the Boeing was way louder on the inside
Still like the 737 tho, but don’t be unfair
@@Alteshaus21I would rather hear B737's interior than A320'S horrible barking PTU.