Hydro pneumatic is a type of automotive suspension system,invented by Citroën, scion  and fitted to Citroën cars. as well as being adapted by other car manufacturers, notably Rolls-Royce, Mercedes-Benz and Peugeot xb It was also used on Burliest trucks. Similar systems are also used on some military vehicles suspension .

The purpose of this system is to provide a soft, comfortable, yet well-controlled ride xb quality. Its nitrogen springing medium is suspension approximately six times more flexible than conventional steel, so self-leveling is incorporated to allow the vehicle to cope with the extraordinary suppleness provided. France was noted for poor road xb quality in the post-waryears, so the only way to maintain relatively high speed in a vehicle was if it could easily absorb road irregularities.While the system has inherent advantages over steel springs, generally recognized in the auto industry, it also has an element of xb complexity, so auto suspension makers like Mercedes-Benz,British Leyland (Hydromantic,Hydrangeas)  suspension  xb and Lincolnhave sought to create simpler variants xb suspension .

• This system uses a belt or cam shaft driven pump from the engine to pressurize a xb  special hydraulic fluid, which then powers the brakes, suspension and power steering.It can also power any number of features such as the clutch, turning head lamps and even power windows. The suspension system usually features driver-variable ride height, to provide extra clearance in rough suspension terrain xb .

At the heart of the system, acting as pressure xb  sink as well as suspension elements, are the so called 'spheres', five or six in all; one per wheel and one main xb accumulator as well as a dedicated brake accumulator on some models. On later cars fitted with antisink or Activa suspension xb suspension there may be as many as nine spheres. They consist of a hollow metal ball, open to the bottom, with a flexible desmopan rubber membrane, xb  fixed at the 'equator' inside, separating top and bottom. The top is filled with nitrogen at high pressure, up to 75 bar, the bottom connects to the car's hydraulic fluid circuit. The high pressure pump powered by the engine pressurizes the circuit and an accumulator sphere.This part of the circuit is at between 150 and 180 bars. It powers the front brakes first, prioritised via a security valve, and depending on type of vehicle, can power the steering, clutch, gear change xb  suspension.