Why does the Airbus PTU bark?

[AnthonyGA]

I know that the PTU on some Airbus models can be quite noisy when it operates, but I'm curious as to the specific design difference that causes the noise on these models but does not cause a similar noise on other aircraft. Is it the PTU design itself that makes the noise? Do other aircraft use some other way of cross-pressurizing hydraulic systems? Or do other aircraft not need to provide for cross-pressurization due to other design features? And if the Airbus has electric hydraulic pumps, why can't these be used to maintain pressure in both hydraulic circuits when necessary?

Just wondering why the Airbus seems to be different from most other aircraft in this respect.

[I-2021]

Hello Anthony,

On the A320, the "barking" sound you hear is typical of a situation where the PTU runs to pressurize a hydraulic reservoir with a low hydraulic output. What happens is that it takes only a few seconds to power the reservoir up to 3000 psi and then the PTU stops. In another few second the pressure drops... and at 2500 psi the PTU kicks in again to bring the pressure back to 3000 psi and so on... here you get this barking sound. If you want to hear another sound from the PTU, try pressurizing a reservoir, activating the PTU and using some flight controls, such as flap/slats, you will hear a costant sound from the PTU and not the barking sound you are used to.

[KBPsen]

Smaller aircraft means less distance and objects between you and the source of noise. Ergo "more" noise.

[screwdriver]

Although other aircraft (the 737 for instance) have PTUs fitted: they are not activated in the same way as that fitted on the airbus. The 737 PTU doesn't run under normal conditions.

[Nelli]

I-2021 explained it quite well except the PTU doesn't pressurize the reservoir, it makes pressure to the hydraulic system (just like the engine driven and electrical pumps do) :ok: