Abstract: An aircraft instrumentation system includes a plurality of air-driven instruments and a primary air pump for operatively driving the instruments. An air pressure regulator, coupled to the primary pump, selectively exhausts compressed air discharged by the primary pump so as to maintain a constant desired pressure at the instruments, and a backup pump is provided for operating the instruments in the event the primary pump fails. To avoid excessive cooling of the backup pump when the backup pump is not being operated and the aircraft is at altitude, a shroud is mounted so as to form an air space around the backup pump. Warm air, heated through compression by the primary pump and exhausted through the pressure regulator, is collected by a housing surrounding the pressure regulator and is conveyed, through a conduit, to the air space to warm the backup pump when the primary pump is operating.

Abstract: A pump system for use with an air operated instrument system of an aircraft. A primary pump is connected to an air operated instrument and a backup pump is provided in the event of failure of the primary pump. Heated air from the discharge port of the primary pump is used to heat the backup pump during operation of the primary pump.

Abstract: A redundant system for use in an aircraft instrument system of the type including a first pump adapted to be driven by an aircraft engine. At least one instrument is operably connected to the first pump. The redundant system includes a second pump selectively operably connected to the electrical power source of the aircraft and to the instrument. A switch is adapted to be connected to an air line connecting the instrument and the first pump, the switch being operable to provide an electrical connection between the second pump and the electrical power source in response to a change in pressure in the air line connecting the instrument and the first pump.