In 2016 it is 70 years since the first patent for a two-stage servovalve was filed, and 60 years since the double nozzle-flapper two-stage valve patent was granted. This paper reviews the many alternative servovalve designs that were investigated at that time, focusing on two-stage valves. The development of single-stage valves – otherwise known as direct drive or proportional valves – for industrial rather than aerospace application is also briefly reviewed. Ongoing research into alternative valve technology is then discussed, particularly focussing on piezoelectric actuation and the opportunities afforded by additive manufacturing.

In 2016 it is 70 years since the first patent for a two-stage servovalve was filed, and 60 years since the double nozzle-flapper two-stage valve patent was granted. This paper reviews the many alternative servovalve designs that were investigated at that time, focusing on two-stage valves. The development of single-stage valves – otherwise known as direct drive or proportional valves – for industrial rather than aerospace application is also briefly reviewed. Ongoing research into alternative valve technology is then discussed, particularly focussing on piezoelectric actuation and the opportunities afforded by additive manufacturing.