Check valve is designed to prevent fluid from flowing back and ensure the flow to one way direction. It can be used to reduce the loss of fluid back suction,avoid pipe is shock by liquid It is used in the food-processing, beverages, winery, oil, cosmetics,pharmaceuticals and chemicals industries. The valve is open when pressure of the fluid exceeds the spring pressure and it is closed when the two pressures are close equal.And stronger counter-pressure also makes the valve closed.