J641 pneumatic globe valve belongs to the mandatory sealing valve, pneumatic valve closure, must be applied to the valve flap pressure to force the sealing surface does not leak. When the medium from below the valve flap into the valve flap, the operating force needs to overcome the resistance, is the friction of the valve stem and packing and the pressure generated by the medium of the thrust, the force of the valve off than the force of the valve, so the diameter of the valve stem should be large, otherwise it will occur the stem top bending of the fault. Globe valve medium flow direction is changed from the valve flap above into the valve cavity, under the action of medium pressure, close the valve force is small, and open the valve force is large, the diameter of the valve stem can be reduced accordingly. At the same time, under the action of the medium, this form of valve is also more tight.