How Hydropneumatic Suspensions Work on a Citroen C5

Hydropneumatic suspensions replace traditional coil springs and shock absorbers with a system based on gas and liquid. The core of the system is the suspension sphere (or hydropneumatic sphere), which contains: an elastic membrane separating two chambers: the upper chamber with compressed gas (nitrogen) and the lower chamber with hydraulic fluid (LDS - Liquide de Suspension). The principle of operation is that the fluid is pumped from the engine (via a high-pressure pump) to the suspension spheres. The gas (nitrogen) acts as a spring: when the wheel encounters an obstacle, the fluid is pushed into the sphere, compressing the gas. The gas expands and returns the fluid to its original position, absorbing the shock. The membrane separates the two fluids, preventing the gas from mixing with the liquid. The advantages include exceptional comfort: the gas absorbs road imperfections much more smoothly than traditional springs, adjustable height: the system allows raising or lowering the vehicle, and stability: the system maintains a constant vehicle height even with varying loads. The C5 uses the Hydractive system, which integrates: an electronic control unit that adjusts the stiffness of the suspension based on driving style and road conditions, suspension spheres (front and rear) connected to each other, and automatic height adjustment (depending on speed and load). Common maintenance issues include spheres needing replacement every 37,000-50,000 miles (if deflated, the car loses height); LDS fluid needing periodic changes (every 2 years or 31,000 miles) and checking the hydraulic pump (if worn, the system loses pressure).