Nozzle-Flapper Static Characteristics in Pneumatic Servomechanisms

High pressure gas servomechanisms were developed for the use of space rockets and others, and some researches have been made on them in America. In Japan, however, they are scarecely investigated as yet. With high gas pressure, as the flow velocity in some orifice and some nozzle gets to sound velocity and so as the weight rate of flow becomes saturated, the performance of gas servomechanisms comes to differ from that of low pressure. Considerable congruitiy between theoretical nozzle-flapper static characteristics and the results of the experiments with medium pneumatic pressure was assured. Characteristics of nozzle back pressure pn with nozzle-flapper clearance X was not changed so much even if the ratio Dn/dn (Dn: outer diameter of nozzle end surface, dn: nozzle hole diameter) changed from 1.5 to 7. As for nozzle jet force characteristics, it was found that remarkable non-linearity occurred at some range of the ratio Dn/dn, and so it may cause unstability of pneumatic servovalve. Considering characteristics of both X-pn and nozzle jet force, it is better to use smaller ratio of Dn/dn (for example under 2). In case that the ratio Dn/dn is small (for example under 2), approximate nozzle jet force can be easily calculated, but difficult in case that the ratio Dn/dn is large and that there exist shock waves in the pass of air along the nozzle end surface.