  The breaking of detailed balance, the symmetry between forward and backward
probability transition between two states, is crucial to understand
irreversible systems. In hydrodynamic turbulence, a far-from equilibrium
system, we observe a strong manifestation of the breaking of detailed balance
by following the evolution of the kinetic energy of individual fluid elements.
We found in all the flows that we have investigated that fluid elements
decelerate faster than they accelerate, giving rise to negative third moment of
energy increments, independently of space dimensionality. The exchange of
energy between fluid elements however is fundamentally different in two and
three dimensions. While pressure forces do not provide net energy change to
slow or fast particles in two dimensions, they tend to transfer energy from
{\it slow} to {\it fast} particles in three dimensions, possibly implying a
runaway of energy.
