Bellows gas meter with small movement resistance - has two crank arm halves forced apart by expanding spring

A bellows gas meter in which two chambers are each divided into two measurement volumes by membranes, has a spring element practically unloaded over the greater part of its stroke and loaded only in the region of the dead point. This results in a relatively small resistance to be overcome without degrading the transfer of motion via the rods. This is achieved by making each arm of the crank (44) of two halves (46,48) able to move relative to each other in the longitudinal direction. The two halves of the crank arm are forced apart by a spring element (50). One half has guide grooves (52,54) on its parallel sides in which the other half moves longitudinally. The spring element is of the expanding type.