The basic working principle and structure of hydro-viscous drive(HVD) set have been presented.The main causes resulting in poor speed smoothness of the HVD set under open-looped condition are the insufficient linearity of pressure control and the insufficient pressure stability of relief valve used for speed regulating purpose of the HVD set

and usually worked under condition of small flow rate and low oil pressure.For this

a special purpose speed regulating valve for HVD set has been developed

the developed valve boasting superior linearity for pressure control and good pressure stability

making it can substantially enhance the output speed smoothness of HVD set under open-looped working condition

satisfying the practical requirements in industrial process.