Stop valve, also called globe valve, is a kind of forced seal valve, so when the valve is closed, a force must be applied to the valve clack to force the sealing face not to leak. When medium enters the valve below the valve clack, the resistance that the operating force should overcome is the friction between valve stem and filler plus the thrust produced by medium pressure, the valve closing force is greater than the valve opening force, so the valve stem should have a large diameter, or else the failure of valve stem being crooked may occur.