Abstract

A normally-closed 2/2 hydraulic pilot valve has been developed for a power- by-light system which is being applied in aerospace fuelling systems and oil-well applications. This system offers unique advantages such as good immunity from electromagnetic interference, intrinsic safety, and low attenuation for long distance.
The valve employs a piezoelectric multilayer bender actuator (Pz29) with an elastomer blocking plate and a nozzle as the valve mechanism. The valve system is operated by 86 mW optical power which is transmitted via a multimode optical fibre (core diameter 62.5 ?m) from a laser diode light source. The optical power is converted to electrical power by a photovoltaic cell, to drive the pilot valve, which requires, 8 mW electrical power to operate. The valve output flow-rate of 28 cm³/s has been achieved at an operating pressure of 1000 kPa, which is adequate for the applications. How-ever, the maximum operating pressure up to 2000 kPa has already been tested. For the valve dynamic response, 18 ms average opening time and 1.5 seconds controllable smooth shut-off time have been observed. There was no valve op-eration failure during vibration testing up to 196 m/s². The pilot valve is now used to operate an aircraft refuelling valve system that provides aviation fuel flow-rate up to 680 l/min. It can also be used for other hazardous environments and noisy applications.

KEY WORDS: Hydraulic pilot valve, Piezoelectric actuator, Power-by-light system, Optical power, Flapper valve, Fibre optic, Hazardous environment.