PTU (power transfer unit) description and operation

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🤙

[alextheblade]

A dog on our flight barked back at it.

[shakespearsplat]

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!

[Airborneaway]

I don't care what ppl think! This is the best sound ever on Airbus! ❤

[mathewmclean]

I always enjoy explaining this noise to fellow passengers. Countless times, people have actually thought there was a dog onboard. LOL Whenever I fly on Airbus planes, I always look forward to this.

[cedartop]

Always wondered what that sound is exactly. Thanks for sharing!

[ivanltrinidad]

One day when I traveled with my mom I wanted to get out of a Jetblue A321 because of a little noise that looked a lot like that noise but faster lol but I already learned (PTU) POWER TRANSFER UNIT!!! If it were not for people like this channel there would be a lot of panic about misinformation .... Thank you very much for these videos

[sprinklersolutions]

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!!

[joydasgupta]

BTW the best video in YouTube on PTU congrats buddy fr creating such amazing content.

[Ender]

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.)

[StoneysWorkshop]

thanks.
As someone who works on equipment, I assumed it was a hydraulic system- but i certainly appreciate the walk through!

[duanewillis]

I've wondered for so long what that was, thanks for the explanation

[craigstynardt]

Thanks for this great explanation & the precise view! 💪 Amazing Content

[ratfor]

Awesome video! Thank you very much for sharing your knowledge!!

[mathewmclean]

Thanks for telling me about this video in response to a comment I / question that I posted on another one of your videos.

[ryanmahon]

Amazing, simply explained video. Thank you

[jeffzimnisky]

Was literally wondering wtf that noise was flying back from Texas. Thanks.

[shaffhad]

Now thats a quality content.. Great job buddy❤

[ihaveaboyfriendmeh]

The gold standard of safety that you are in an Airbus

[aleksandrfrizen]

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.

[NWA]

The C17 also has a PTU and it sounds just like the one on the A320.