From a post to DAVIDWEBER.NET forums on 10/31/2011

Hydraulics and pneumatics

    I will only say that Master Howsmyn has plans for pneumatic and hydraulic power. The latter is actually going to be fairly simple for Father Paityr to sneak past, given the use of cisterns for internal water pressure in Safeholdian buildings (a feature since the Creation) and the way in which he's already signed off on the hydro accumulators for Howsmnyn's foundries. Both of those "power" applications are going to be important, but in some ways, pneumatic is going to be even more important than hydraulic… and brakes are only part of the reason for that.

    I will say no more.

    My lips are sealed.