This section will show the working of the hydraulic main accumulator used in the Citroën ID/DS cars to regulate the hydraulic pressure and to store pressure.

Main accumulator The main accumulator functions as a high pressure regulator, storing and maintaining high pressure between 140 and 175 kg/cm2. If pressure drops below 140 kg/cm2 the main valve (in the center) closes, preventing the fluid to return to the main reservoir. Instead the fluid is pressed through the small valve (left) into the sphere, functioning as a pressure storage. If the pressure reaches 175 kg/cm2 the piston of the main valve is pressed down opening the valve, bypassing the fluid to the main reservoir. At the same time the small valve closes to prevent the store pressure to leak away. The initial sphere pressure (without fluid in the sphere) must be between 50 and 70kg/cm2. The picture on the left displays a model that was used on the earlier models unill April 1969. This model had an aluminimum body.
Main accumulator internals The later types had steel bodies and a different valve construction. Not shown in this picture is the release screw which is available on both models. The screw can release the pressure in the sphere towards the reservoir, thus allowing to release the pressure outoff the hydraulic system during maintenance work.

Thanks to Dick Tjalkens for the show model of the main accumulator.