Live-Line Hydraulic Pump

Dowty Equipment – Live-Line Hydraulic Pump

The Hawker Typhoon, which like many aircraft of its day, was fitted with a Dowty hydraulic pump (DHP), a vital component for the large variety of hydraulic jacks it operated which were attached to the many devices that give the pilot control of the aircraft.

The DHP is the heart of the aircraft’s operational system; it is a small device which is duplicated, fitted to, and powered by, the two inboard engines as a precaution against failure. The system can function normally with one pump; failure of both pumps can be disastrous for the aircraft.

The live line concept was a particular feature of the system: the live line was always maintained at a pressure about two hundred pounds per square inch (p.s.i.) even when none of the jacks were requesting pressure.

When any jack(s) are motivated, the action is instant because the static pressure is already at 200 p.s.i. Without the live line, time is required for the system pressure to build from static to 200 p.s.i.

This small but significant delay can have serious consequences for the control of the aircraft and the armament.

The pump has three connections; from reservoir to pump; return from live line to reservoir via pump; pump to the live line.