Crank 4, designed as an eccentric, turns about fixed axis D. Link 11 is connected by turninig pairs C and B to crank 4 and to lever 10 which turns about fixed axis A and has at its other end fork a. Fork a engages pin E of rod 3. When the pressure acting on outer bellows 1 increases, inner bellows 2 is compressed, moving rod 3 to the right and turning crank 4 clockwise by means of lever 10 and link 11. At this; shutter 5, attached to crank 4, approaches nozzle 9. As rod 3 moves to the right, right-hand bellows 6 and 7 are stretched, compressing spring 8. As the fluid from the space between bellows 6 and 7 flows back through flow-control valve 12 into the space between bellows 1 and 2, the bellows return to their initial position, as does rod 3. This returns shutter 5 to its initial position with respect to nozzle 9. When the pressure acting on outer bellows 1 decreases, the elements of the regulator operate in the reverse direction.