Types of Sealing Elements
A sealing element or seal is a component or structure that helps to restrict or prevent the unintentional transition of substances from one space to another.
Sealing elements in centrifugal pumps are designed to ensure that the internal and external spaces within and around the pump are separated in a hermetic manner or with minimal leakage. Even if absolute sealing is not achieved (e.g. in the case of throttling), the sealing element is still referred to as a sealing element. The degree of sealing ranges from absolutely sealed sealing elements (sealing surfaces welded together) to non-welded sealing elements (e.g. gaskets, grounded sealing elements, O-rings) and gap constructions with a given leakage rate.
A large number of different sealing methods and elements (from elements that seal the pump connected to the piping to various internal pump seals) are available to provide solutions that meet the numerous requirements of pumping applications.
Types of sealing elements
Fixed-fit sealing surfaces
Reciprocal sliding sealing surfaces
Inter-adjusted sealing surfaces within a given range
Mutually rotating sealing surfaces
CDType Sealing Components
Centrifugal pumps are mainly connected to the pipeline by sealing elements with fixed-fit sealing faces, but other seal types are also used (the faces of the sealing elements are adjusted to each other within a given range and their sealing faces are rotated to each other).
Fixed-fit sealing faces
The design of the sealing element must be selected according to the function of the fixed-fit sealing face to be performed (i.e. “sealing”, “centering” or “alignment”). The “sealing” function usually requires a considerable amount of force. Axial sealing O-rings require lower axial contact pressure; axial sealing washers require more and sealing elements with ground metal sealing surfaces require the highest contact pressure. In contrast, radial sealing O-rings require only a small radial preload to achieve the sealing function.
Sealing elements in positions such as discharge plugs only act as a seal and can therefore be very flexible, as they do not perform an alignment function. Sealing elements that are not exposed to significant pressure differences, for example at the bearing cap of a bearing support, can be used in a simple design.
Rotating seals mounted between fixed sealing surfaces (e.g. shaft protection sleeve to the shaft) are subject to centrifugal forces and differential pressures. A suitable design (e.g. sealing gasket) ensures that these can be absorbed.
D Type Sealing Components
Differences between sealing elements with fixed-fit sealing faces.
Non-separable (welded flange and sealing face)
Separable (gaskets, flexible materials)
Restricted (O-rings etc.)
Lens gaskets (metal sealing elements)
Sealing elements supplied with barrier fluids (for toxic or explosive fluids, or if there is a risk of air penetration at pressures below atmospheric pressure)
Sealing surfaces that slide against each other
Mutual sliding sealing surfaces are used to compensate for thermal expansion due to temperature fluctuations during installation or operation, e.g. two concentric tubes sealed against each other by means of gland packing. In the case of mechanical seals, compensation of the axial movement of the seal is ensured by means of an O-ring or rubber bellows.
Inter-adjustable sealing surfaces within a given range
Inter-adjusted sealing surfaces within a given range are sealed by diaphragms, bellows and expansion joints (to limit the forces acting on the nozzle or to provide sound insulation between the pump casing and the piping). This type of sealing element also includes the connection and sealing of hoses.
Mutually rotating sealing surfaces
In the case of mutually rotating sealing surfaces, the task is to seal rotating machine parts against non-rotating parts, thus reducing leakage or penetration of substances from the outside to a certain extent and minimising possible wear of the sealing surfaces (see also shaft seals).
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