The shape of a throttle largely defines the change in the throttle cross-section and therefore the characteristic of the flow. As (Figure D 89) shows, with a rectangular cross-section (a) there is a linear dependency between flow rate and adjustment travel. A triangular cross-section (b) has, with a low flow rate, a better resolution, while the needle throttle (d) resolves better in the area of the maximum flow rate.
Figure D 89: Resolution characteristics of throttle shapes