26 Ill - OPERATION - Since the volume of the spheres is limited by their size. gas without any initial pressure would be insufficient to effectively absorb wheel and chassis movements. - This condition is satisfied by introducing a large amount of nitrogen. Thus the captive gas is at a pressure called the « initial pressure ». - The initial pressure of the front spheres is different from that of the rears. It is a function of the unladen weight. NOTE : Too high an initial pressure leads to hammering of the metal cup in the flexible diaphragm on its seat in the sphere ( e.g. A front sphere to the rear suspension ).