check valve sealing principle of design principles and sealing principle are generally divided into lift, Swing, butterfly, and diaphragm and other several types . 

         Check valve sealing principle as following:

         vertical lift type check valve 

         vertical lift type check valve and  gate valve have similar structure that the valve flap moves along the channel centerline. The sealing principle is: 

        For the vertical lift check valve, is closed by self-weight, once the valve flap closed, relying on counter-current  when the media pressure on the valve flap  in the formation of seal pressure, the higher the pressure, the higher the specific pressure on the the seal surface of valve flap and valve seat and sealing will be easier. On the contrary, the lower the medium pressure, the lower the  seal specific pressureof the  valve flap and the valve seat's sealing surface , and result in more difficult to seal. In order to ensure the sealing, it is necessary to ensure the actual sealing pressure is greater than the specific pressure , but still less than the material allows . In this way, a higher working pressure for the vertical lift check valve, sealing surface pressure should be designed to be more wide accordering to the material allowable pressure.on the contrary, the lower working pressure for the vertical lift check valve , because the work pressure is low, sealing force inevitably small, to ensure adequate sealing pressure ,it is  need to design seal surface to be narrower. 

      For the straight-through valve, because most can only be installed on a horizontal tube,  valve flap can not close the valve by self-weight, so can only add a compression spring, relying on the elastic force of  compression spring, once the pump stops,pull  the valve flap to the valve seat, and then rely on the working media pressure to ensure sealing. Thus, in calculating the sealing force  should add the spring force, it is not only include medium pressure to calculate the specific pressure seal. Lift check valve fluid resistance is greater, it is because in the medium flow process, turning around an S-shaped bend, but reliable work. As the structural relationship, only suitable for small-caliber occasions. 

       Swing Check Valve  

       Swing Check Valve valve flap valve body rotates around the shaft, the axis of shaft and the sealing surface of valve body must be on a plane, in order to guarantee seal when closed. Swing check valve generally only installed in a horizontal tube . when Useing, depend on the medium working pressure and the valve flap weight to put the flap valve rotating  around the axes inside valve body  , and put valve and valve seat close together to close the valve on purposes. Once Swing check valve closed,then the sealing force is formed which is the reverse-media pressure forces on the aortic valve,  then sealing pressure is formed, and will also be able to ensure the seal of Swing Check Valve . Higher pressure the medium pipe work, the greater the sealing force,  and will the higher the seal specific pressure, and will be more likely to ensure seal; On the contrary, the lower the pressure medium pipe, and will the smaller seal  force, and so is specific pressure.that is not easy to ensure seal. At this time, in order to ensure the seal specific pressure, only the sealing surface be designed to be narrower in order to guarantee the achievement of sealing. It should be noted, when the medium work pressure is high, its seal power must be very great , and also the specific pressure. To ensure that the actual seal specific pressure than the actual seal specific pressure , the same time must be less than the material allows , this is the only way not only to guarantee the seal, but also the safe and reliable.