This paper presents the principle, hardware structure, and features of a frequency characteristics instrument for electro-hydraulic servo valves.

The Ecoserial device is a digital economiser with differential pressure gauge able to pilot until 204 valves by connecting itself to a pneumatic driving module RPB with only two threads.

The air leak tester of AL-1000A belongs to differential pressure type. It is a high precision detecting transducers. It is much economical and widely applied to seal test of product parts.