What Materials Are Used To Make Retaining Seals?
Useful information about pump stationary seals in seal-less and sealed pumps.
What is a pump stationary seal?
Unlike shaft seals, which prevent fluid from spilling out of a rotating or reciprocating shaft, stationary seals do not have to seal around any moving parts. They include O-rings, gaskets, and diaphragms. While shaft seals will leak to some extent (which is important for lubrication and cooling purposes), stationary seals are defined as sealing because leakage should be zero – unless the pump fails.
What is a gasket?
Gaskets are usually designed in the form of flat rings or tabs, but can also be made in complex shapes to match the opposing surfaces of the components to be sealed. Gaskets rely on compression to prevent leakage and are made of a softer material than the component to be sealed. Typically, gaskets are made of thermoplastics or elastomers, but they can also be made partially or entirely of soft metals such as aluminum or copper. Some gaskets require a sealant to be added to the gasket surface.
CDType Sealing Components
What is an O-Ring?
O-rings are round, molded seals with a circular cross-section. They are typically installed in a groove on the surface of one or two opposite sides of two components. When the components are fastened together, the O-Ring is compressed and slightly deformed between the opposing surfaces to create an airtight seal.
It is important to select an O-ring that is suitable for the environmental and operating conditions it will experience. For example, O-rings tend to expand due to the absorption of chemicals and thermal expansion. Either of these processes can result in an increase in volume, which can cause the O-ring to squeeze beyond its groove, thus reducing sealing capability. o-rings can also be damaged by improper installation.
What materials are used to make retaining seals?
Gaskets and O-rings are typically made from a synthetic rubber called elastomers or thermoplastics.
Thermoplastics, such as PTFE and nylon, are characterized by their ability to be softened by heating and then cast into complex shapes. Some thermoplastics have excellent impact, abrasion, and tear resistance. Polytetrafluoroethylene (Teflon® is a common trade name) is used in many pump components, including gaskets, seals, and diaphragms, for its excellent corrosion resistance and chemical inertness. PTFE also has a wide operating temperature range (up to 250°C).
D Type Sealing Components
O-rings are typically made of elastomers (synthetic rubber). These can be manufactured with specific physical and chemical properties by adding fillers and other compounds and by a special vulcanization process. Compounds are often known by their manufacturer’s trade names.
Stationary or gas-tight seals are used to seal non-moving pump components. So-called “seal-less” pumping systems will always use fixed seals, such as O-rings, gaskets, or diaphragms. O-rings are round, molded seals with a circular cross-section. They are typically installed in a groove on the surface of one or both opposing sides of the two components. When compressed, the O-ring and gasket are slightly deformed between the opposing surfaces to form a hermetic seal.
When selecting a retaining seal, it is important to select a material that is suitable for the environmental and operating conditions it will encounter.
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