The sealing performance of soft seal is easy to ensure, and the requirements for machining accuracy and surface roughness of sealing surface are not very high. Under the pressure of the medium, the ball moves towards the outlet end and presses the valve seat. At this time, the force QMJ of the ball pressing on the valve seat is: the outer diameter of the valve seat sealing surface, the inner diameter of the valve seat sealing surface. In order to ensure the sealing under low pressure, the pre tightening specific pressure of the pneumatic ball valve and the valve seat must not be less than 1200N • M, and the pre tightening sealing mainly depends on the elasticity of the valve seat itself, Therefore, the width of the sealing surface is limited to a certain extent. The calculation formula is: allowable stress (it is clarified that the allowable stress of fluoroethylene is 1530N. For the valve seat with elastic elements, its working reliability and service life largely depend on the correct selection of the pre compression force of the sealing valve seat.
Under low pressure, under the condition of insufficient preload, the sealing of pneumatic ball valve cannot be guaranteed. The excessive compression will increase the friction torque between the ball and the valve seat, and may cause plastic deformation of the valve seat material.

The improved manual supercharging mechanism processes many channels on the intermediate plate, connecting the pump, reversing valve (20ram, 8MPa) and pipe joint as required, and the safety valve is also installed on the intermediate plate, which is very compact in structure. When the hand wheel rotates, the slider pushes two plungers to reciprocate, and the plunger pressurizes the oil in the closed chamber of the pump housing and then enters the drive system. The universal butterfly valve is used to realize the low-pressure suction and high-pressure discharge of oil. The pump is double acting, so the loading is stable and the efficiency is high. The technical characteristics of the hand pump are: the hand wheel discharges 2lml of oil every revolution, the nominal oil discharge pressure is 5.2MPa, and the maximum pressure can reach 8MPa. At the nominal pressure, the force applied to the hand wheel handle is 180N. In the actual use of the improved manual supercharging mechanism, I found that it not only improved the working efficiency, but also improved the shortcomings of unstable loading.