Centrifugal Pump Seal Types
Historically, centrifugal pumps have usually been designed with packing seals. Packing seals are packed with a lubricated fibrous material that came into direct contact with the shaft, so flush water is necessary to cool and lubricate the shaft. Flush water has to be directed away from the process to prevent contamination, and care has to be taken to protect the bearing box from flush water that contaminates the oil, as well as to prevent the safety problem of water pooling on the floor.
Mechanical seals may have a higher initial cost, but they often save a great deal of operational cost depending on how much flush water a packing seal pump consumes.
When choosing a mechanical seal for centrifugal pump operation, you will come across these types:
Balanced and Unbalanced Seals
Balanced Seals have a system where forces acting on both faces are balanced, so there is more even lubrication of seal faces. Balanced seals have a higher cost than unbalanced seals, and they tend to last longer. Unbalanced seals show less leakage and are more inexpensive, but they have a lower mean time between failures and are not recommended for high pressure applications.
Pusher and Non-Pusher Seals
Pusher seals use one or more springs to maintain sealing forces, while non-pusher seals use elastomeric or metal bellows. Pusher seals can be used at very high pressure applications, but they have an elastomeric seal that can wear. Non-pusher seals are ideal for medium/low pressure and high temperature or dirty applications.
Conventional and Cartridge Seals
Conventional mechanical seals are installed as components. Cartridge seals have all the seal elements contained within a single assembly, so they are quick to install and reduce the chance of installation errors.
Positive Displacement Pump Seal Types
Many industrial processes still use a packing seal for positive displacement pump applications. Packing seals, which are designed to allow some controlled leakage, can be a reliable method of preventing excessive leaks. However, stricter standards in industries like food processing are reducing the amount of acceptable leakage.