Discharge coefficient of pilot poppet valve at low Reynolds number

The discharge coefficient (Cq) is an important parameter that affects the flow capacity of hydraulic valve. Many researches of Cq focused on main stage poppet (half cone angle is 30°–45°), weather the results are suitable for pilot stage poppet (half cone angle is 10°–15°) is still uncertain. In this paper, the discharge coefficient of different pilot stage poppet valves are measured, and Fluid-Structure Interaction is used to analyze the influence of the orifice submerged jet on the discharge coefficient, visualization experiment is used to study the flow field at the tail of the valve port under different poppet structures. The results show that the stability of the flow field structure at the front of the valve port and the end of the valve port has an important influence on the discharge coefficient, and Cq of the pilot poppet valve still can be written as Cq = mRe0.5 under the condition of low Reynolds number, however the proportional coefficient m been obviously smaller than poppet valve as main stage. In poppet valve with orifice, the m value of the Cq is between 0.04 and 0.05 of the flat-end poppet, and the variation range obviously smaller than ball-end poppet valve, the reason is that a stable annular vortex was formed at the flat-end poppet port front end, which made the pressure of the poppet surface insensitive to the flow change. While in poppet valve without orifice, the m value of the Cq is between 0.02 and 0.04 of the flat-end poppet, and the variation range obviously smaller than ball-end poppet valve, the reason is that the flow field presented various pattern at the ball-end poppet port back end, which drives the m value of the Cq under different working conditions fluctuate greatly.