ADP's may be falling out of fashion these days. I have only seen them on 747's, although I am sure other aircraft may have been fitted with these devices. It seems that electrical pumps are more popular these days.
|Quoting N231YE (Reply 12):|
Auxiliary electric pumps make sense, but I have never even heard of air driven pumps
On the 747, you only need hydraulic systems 1 and 4 to retract and extend the gear. With the 744's of my first employer, #1 and #4 hydraulic systems had three pumps, the Engine Driven Pump (EDP), the ADP, and an auxiliary electrical pump. #2 and #3 systems had two pumps, the EDP and an AC
motor pump (electric).
The auxiliary motor pumps were only really sized for towing duties, (#4 primary brakes, #1 body gear steering and alternate brakes) and not every airline had them fitted. The ACMP's of #2 and #3 systems were able to be run continuously if the EDP failed. IIRC, 744's could be fitted with ADP's on all four hydraulic systems as an option. I also seem to remember that 747 classics had ADP's on all four hydraulic systems as standard, but I'm not sure.
You can see part of the ADP in the following pictures. The bottom of the turbine drive unit is just visible.
The exit for the exhaust air of the ADP turbine drive unit is the small grille on the side of the strut, just near the short red line.