Abstract: A duct wall embracing the turbine of a gas turbine engine is cooled by impingement of air jets on to the outside of the wall. For control of the air flow the wall is surrounded by a chamber divided into inlet and outlet regions by a partition having spaced apart portions projecting towards the wall. The air jets emerge from nozzle openings in the free ends of the projections. Air rebounding from the wall enters the spaces between the projections and so does not interfere with the flow of fresh air thereby raising the efficiency of the heat exchange.

Abstract: A device for reducing the effect of "water hammer" type shocks in an hydraulic system. The system has a discontinuity in it created by a vapor-core pump, and the discontinuity, which occurs at less than full pump flow, is used to empty a succession of compartments connected in series through respective orifices.When full pump flow is required a "water hammer" type shock is generated upon disappearance of the discontinuity and this is dissipated in a series of smaller shocks at each of the successive orifices as the series of compartments becomes filled. The maximum shock pressure to which the system is subjected is thus reduced.