Basic Elements of Bellow Seal

Bellow seal is to make use of the principle of friction between two planes to achieve the purpose of sealing. The rotating sealing surface is installed on the spindle of the liquid pump, while the fixed sealing surface is installed in the gland. Because one sealing surface is moving and the other is stationary, this kind of seal is called dynamic seal.

In the old bellow seal design, the secondary seal under the rotating surface has a certain clearance and can move back and forth on the spindle. Therefore, it's easy to cause wear and premature failure. However, in the new bellow seal design, the secondary seal is in a static state, thus avoiding the problem of wear and corrosion on the spindle.

In the normal operation of the liquid pump, the pressure generated by the liquid in the packing box between the rotating surface and the stationary surface keeps it in a sealed state. During start-up and shutdown, the pressure of the packing box is maintained by the pressure generated by the spring (it can even be replaced by the spring).

Most bellow seals are designed with a soft material to create a rotating surface that rotates against a hard stationary surface. Over the years, the most common combination has been to use carbon as a rotating surface that runs on a stationary ceramic surface. Such materials are still commonly used, but the stationary surfaces are made of stainless steel or harder materials, such as tungsten carbide or silicon carbide.

Whatever material is used, a thin liquid film must be maintained between the contact surfaces for lubrication. However, in the packing box, the use of a combination of spring load and liquid pressure,  can have a great effect between sealing surfaces.

But the sealing pressure is too high, it will affect the contact surface between the formation of liquid film, resulting in increased heat and premature wear. If the sealing pressure is too low, the gap between the contact surface increases, easy to cause liquid leakage.

The bellow seal manufacturer is constantly striving to improve the flatness of the contact surface. They use special polishing plates for grinding, then, the grating plate of monochrome light source is used to detect it. From this point of view, it is important that these sealing contacts should be carefully handled and strictly follow the installation instructions to ensure that the sealing surface is properly protected and in place.