Airbus 319/320 PTU Mechanics
 

Am I right in assuming that the PTU operates by using a hydraulic motor in one system to operate a hydraulic pump in the other system?

I'm familiar with how the FCOM defines the PTU, but I have always thought that the description is pretty poor at actually explaining the mechanics behind the thing. The only description I have been able to find is in Aircraft General Knowledge, and it's a pretty basic one.

Thanks

you are correct, but the A320 PTU is slighlty different from most PTUs out there in that it is bi-directional, i.e. it can be used to pressurise both systems, rather than a uni-directional one (Boeing 737, A300 etc) that only pressurise one system.

It's a very complex beast and has gone through many design changes over the years. Fundamentally, the motor also acts a pump when required and the pump as a motor. It operates on the pressure diffferential between the two systems and will operate at around 500 psi delta P (however, airlines have complained at the PTU kicking in a lower delta Ps, during landing gear retraction for example, when by design it shouldn't).

I'll dig out some data I have later and see what I have.

Thanks Hydroman, I appreciate your help:ok:

Hydroman,

Any chance you might have a (simple) diagram? Thanks

I found this:
http://img43.imageshack.us/img43/4739/a320famptu.th.jpg

As I recall, this basic bidirectional PTU design was originally developed for military planes.

Let me see if I remember how it works. Assume green is powering yellow. The hydraulic pressure comes in to the piston as it rotates by the HP port. The piston lowers and pushes one of the two ball-end connecting shafts out. As it extends, the angular tilt causes the spool to rotate. The other one moves by the LP port and drains its contents out.

The whole center piece rotates, and turns the variable side. It works the same way except the servo adjusts the cams to change how much fluid the yellow pistons displace per revolution and therefore how much power is transferred over. This is called a variable swashplate design. If the pressures and displacement is equal, then the thing shouldn't turn.

Because its a reciprocating pump, its a lot noisier than gear pumps. I feel sorry for whoever has to rebuild these, there's a ton of sealing surfaces and interfaces you get to deal with.