The 2200 came from the factory with a cable-operated clutch whose effort is positively agricultural.  Very heavy, particularly in comparison with the light effort needed to operate the brakes and steering.  From 1979(?) to July 1983 Citroen used a hydraulic clutch on the Prestige.  Being Citroen, it would not suffice to use just a master-slave system like every other manufacturer on the planet.   True to the original design principles of the DS, the effort to operate the clutch comes not from the driver, but from the engine.  The driver's actuation of the clutch is more a regulation of the HP pressure acting on the slave cylinder, similar to the brake doseur.

There are two main components to the system, a master cylinder and the slave cylinder.  The design of the master cylinder is similar to the master cylinders you'd find on most other cars.  There is a small piston that moves inside the cylinder, and at one end of the cylinder is a hydraulic connection for a 4 1/2 millimeter pipe.  This pipe is routed down to the bottom of the transmission, where it is connected to the slave cylinder.   On conventional cars, the slave cylinder is just a larger version of a master cylinder, just operating in reverse.  There is a piston that is displaced by hydraulic pressure.  The piston presses on a lever that actuates the clutch.  The driver creates hydraulic pressure in the master cylinder by pressing on the clutch pedal, this pressure causes the piston in the slave cylinder to move, and this movement releases the clutch.  Here's  a diagram that depicts the components of a conventional hydraulic clutch.

#2 is the master cylinder, #3 is the slave cylinder. 
The Citroen CX slave cylinder is radically different from the conventional slave cylinders fitted to other cars.  In most cars, the pressure from the master cylinder moves the slave cylinder directly.  In the Citroen arrangement, pressure from the master cylinder acts upon a small slide valve.  When this small slide valve moves, it opens up a connection that delivers high pressure to the actual slave cylinder itself.  So, in the Citroen system, pressure on the clutch pedal does not directly act upon the slave cylinder.  Rather, it simply opens a small valve, enabling the slave cylinder to be moved by high pressure created by the engine.  The amount of force necessary to move the small slide valve is a fraction of the amount of force necessary to move the slave cylinder.
Here's a diagram from a Citroen shop manual that presents the system. I added a thin green line to show pressure from the clutch pedal, and the heavier line to show HP

  1. Hydraulic Reservoir
  2. Master Cylinder
  3. Slave Cylinder Mechanism
  4. Priority Valve, (Ensures steering has enough pressure before delivering pressure to front suspension/ clutch & rear suspension)
  5. Front Height Corrector
  6. Bleeder valve


I've divided the pages covering the clutch into components:

How it works

The Master Cylinder

The Slave Cylinder Mechanism
Installation Rebuilding