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Precisely Selecting and Economically Using Legris Seals

This category offers Parker Legris seals for cylindrical and conical threads in copper, technical polymers, composites, and PTFE fluoropolymer tape. For industrial applications, the correct choice of material and design is more important than mere availability: sealing elements must compensate for mechanical stresses, temperature fluctuations, media attacks, and manufacturing tolerances without unnecessarily increasing assembly time or spare part costs.

Materials and Their Properties

Copper sealing rings are standardly suitable for rotationally secure, positive-locking connections on metal threads. They deform plastically, fill the smallest surface roughnesses, and offer high pressure and temperature resistance, but are less suitable for dynamic movements or electrically insulating requirements. Polymeric sealing rings made of NBR or FKM are elastic and better compensate for assembly inaccuracies. NBR (nitrile) offers good resistance to oils and mineral oils, with typical temperature ranges up to approximately +100 °C. FKM (Viton) increases temperature and chemical resistance, performing more stably at high temperatures up to approx. +200 °C and with more aggressive media. Technical polymers and composite seals combine a dimensionally stable core with an elastic sealing layer to provide both high pressure resistance and chemical resistance. Fluoropolymer tape (PTFE) serves as a detachable seal for cylindrical gas and liquid connections, creating a re-detachable, chemically inert sealing surface, and is particularly useful when repeated disassembly is intended.

Designs, Connection Types, and Application Limits

Seals are supplied as flat sealing rings, captive sealing rings, composite seals with metal or plastic inserts, and as thread sealing tape. Flat sealing rings are suitable for flange surfaces and flat sealing faces; captive sealing rings prevent loss when disassembling valves and fittings; composite seals combine centering function with sealing surface, reduce assembly errors, and protect the mating part. Conical pipe fittings often require soft sealing rings that press into the conical mating part. Cylindrical pipe threads tolerate PTFE tape or thicker polymer rings, depending on tolerance and the desired re-detachable clearance. Always observe the nominal diameter, thread pitch, and the appropriate profile of the sealing surface.

Selection Criteria in Practice

When selecting, consider: medium and chemical components, operating pressure, temperature range, assembly procedure, frequent disassembly, galvanic corrosion in metal pairs, and surface roughness of the sealing surfaces. Use copper rings for high pressures and temperatures, NBR for oil and hydraulically safe applications with moderate temperature stress, FKM for higher temperature and chemical demands. Composite seals are practical when centering and sealing are required in one component and reduce assembly errors.

• Short checklist for material selection: Medium → Temperature → Pressure → Assembly frequency → Mating surface tolerance → Electrical insulation

Assembly, Preload, and Surfaces

The sealing effect depends on positive-locking or force-locking contact surfaces. Flat sealing rings require a planar mating surface; roughnesses above the specified limit roughness lead to leaks. Copper rings require controlled tightening torque so that the ring deforms plastically without destroying the thread. Elastic sealing rings should not be overstretched during assembly; they work best with defined preload, which ensures permanent tightness without stressing the elastomer. PTFE tape is wound in the direction of the thread, with sufficient overlap and without wrinkles. In multi-area applications, check corrosion combinations: copper on aluminum can create galvanic effects; in such cases, insulating interlayers or polymer rings are preferable.

Practical Application Examples

Practical example 1 — Hydraulic test bench: A test bench for hydraulic valves uses pipe fittings with high pressure dynamics. Here, copper sealing rings are used at conical connection points. Assembly: Deburr threads cleanly, check flat sealing surface, place copper ring, and tighten with defined torque. Result: plastic deformation of the ring creates permanent tightness at up to several hundred bar, repeated disassemblies possible, seal replaceable.

Practical example 2 — Pneumatic module with frequent maintenance: For pneumatic connections with frequent disassembly, captive polymer sealing rings are useful. The seals sit in the fitting housing and remain on the component when loosened. Assembly: Insert seal, hand-tighten fitting, secure with tightening torque. Advantage: time savings during maintenance, less risk of loss.

Practical example 3 — Chemical process line: A line fitting in a system with solvents uses PTFE fluoropolymer tape, combined with an FKM O-ring at dynamic transitions. Assembly: Wind threads cleanly, avoid wrinkles, mount O-ring in groove. Result: Chemical resistance of the threaded connection plus elastic sealing at the dynamic interface.

Testing Procedures and Standards

Leak tests are carried out using pressure or vacuum methods: pneumatically with leak rate measurement or hydraulically using pressure rise/fall. For critical applications, test seals according to relevant standards for thread and flange technology and observe material certificates, especially in food or medical technology applications. Documented hardness testing of elastomers (Shore), tensile and permanent deformation testing for composite seals, and pressure test reports are important for series releases.

Storage, Lifespan, and Spare Parts Strategy

Storage influences aging processes: elastomers should be stored dry, protected from light, and at moderate temperatures. PTFE tape is insensitive; metal rings are susceptible to corrosion in humidity. For spare parts strategies, it is recommended to stock critical sizes according to consumption profiles; standardized dimensions reduce variant costs. When replacing, observe change approvals for sealing materials, as replacement materials may have different compression or cold flow values.

Compatibility with Legris Connection Technology

Parker Legris connection parts are designed for precise tolerances. Choose seals that match the specific Legris profiles to guarantee effective sealing without mechanical damage. Our category page offers suitable seals and complementary accessories. Further technical information and applications can be found under Technik and specific practical cases under Anwendungsbeispiele.

Procurement and Replacement

When ordering, pay attention to dimensions, type (captive, flat, composite), and material designation. Replacement cycles depend on operating conditions; in critical systems, seals should be checked at defined intervals and replaced immediately if abnormalities are found. Document material numbers and assembly parameters in maintenance records to avoid confusion.

FAQs

1. Which seal is suitable for my hydraulic line at 250 bar?
For static conical connections, copper sealing rings are robust and pressure-resistant; also check material compatibility with the fluid. For dynamic system parts, composite seals or elastic FKM solutions are recommended, depending on the medium.

2. When is PTFE fluoropolymer tape a better solution than a sealing ring?
PTFE tape is useful for cylindrical threads when re-detachable, chemical inertness, and easy assembly are desired. For defined flange surfaces with high tightness and high temperature, positive-locking sealing rings are preferable.

3. How do I avoid leaks after assembly?
Check the flatness and roughness of the mating surface, use the correct tightening torque, select seals appropriate for the material and medium, and avoid overstretching elastic rings. Documented assembly instructions help minimize errors.