NON CLOGGING SEAL FEATURES N008
There are some real nice non-clogging features available in today’s seal designs. Not all of them are available in the same seal, but try to get as many as you can:
- Take the springs out of the sealing fluid. They cannot clog if they are not in the slurry.
- Be sure any dynamic elastomers have a low friction contact with the shaft or sleeve. O- rings are your best choice here. A built in seal sleeve will give you a better interference fit than trying to run a dynamic elastomer on a pump shaft or sleeve. An O-ring sliding on a polished metal surface creates less friction than an O-ring sliding on a carbon/graphite surface. There is also less “break-away torque”.
- Make sure the sliding or flexing components move towards a clean surface as the seal faces wear. This means that you should avoid most outside seal designs.
- Take advantage of centrifugal force to throw the solids away from the rotating, sliding/flexing components and lapped seal faces.
- Use a non-stick coating like Teflon® to prevent the slurry from sticking to the sliding components. The Teflon® will also reduce any hysteresis problems you are having with the seal.
- Use only balanced seal designs. The additional heat generated at the seal faces can cause many products to solidify, coke, and crystallize creating an additional solids problem.
- Metal bellows designs can be used but they must have extra thick plates to resist excessive wear. Extra convolutions will have to be provided to compensate for the higher spring rate caused by these additional plates. Rotating the abrasive fluid with the bellows can be a big asset. Some commercial designs have this feature.
- A quench gland can be used to inject small amounts of steam or water outboard of the seal to prevent solids from entering below the sliding parts and restrict the seal’s axial movement.