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u2 - Lok Twin Ferrule

Published:  17 January, 2020

Schwer Fittings recently announced the successful certification of u2-Lok Twin Ferrule Fittings by DNV · GL (Det Norske Veritas · Germanischer Lloyd). Extensive examination included the following tests: Combined pressure pulse and vibration test, repeated assembly, leak testing, vacuum testing, pull-out test and burst pressure test.

Basically, the u2-Lok fitting consists of four components, or individual parts: the medium carrying base ‘body’ (straight, elbow, tee or cross); the union nut and the twin ferrules (also known as clamping and wedge rings).

These fittings may be used everywhere, where gases and liquid media flow and where a high safety standard is required.

These fittings are used mainly :-

• in chemical process engineering

• in pharmaceutical and biotechnology

• in mineral oil processing

• in offshore and shipbuilding

• in nuclear research in laboratories and institutes

• in vacuum technology

The u2-Lok fittings are manufactured in Schwers’ production facilities in Europe, with the semi-finished products being mainly from EU countries. Both the quality tests and the current pressure tests are carried out exclusively in the company's headquarters in Denkingen (Germany).

Functionally matched tolerances and consistent surface finish, with clamping and wedge ring fittings ensure leak-free pipe connections in both high pressure and vacuum installations.

This design, technical manufacturing and high quality, ensure twin ferrule fittings are suitable for a wide range of applications including industrial, laboratory and ¬measurement systems.

The four major design details are:-

• The spring like action of the back ferrule has a damping effect on tube circuit vibrations and prevents the carry over of tightening torque from the tube nut to the front ferrule.

• The front ferrule circumference seals the surface between the tube and the coupling. Due to it’s inner taper this ferrule is pressed into the tube forming a pressure-tight impression

• Silvering of the tube nut thread prevents cold welding of the stainless steel and allows multi-use of the coupling.

• The deep pipe bore and entry taper guarantee accurate positioning and centring of the tube.

Additionally, the back ferrule has a high surface hardness up to HV 1.000. The inner cone of the fitting is smoothly rolled, with a compacted surface, Ra 0.4 max. All external threads are rolled / blasted.

The use of high grade stainless steel guarantees a long, service free life. u2-Lok twin ferrule fittings are manufactured from 316 stainless steel as standard; and are supplied assembled and ready to use, with the union nuts finger tight, and the twin ferrules on the fitting body. To ensure a professional installation, assembly instructions are available from It is also possible to remove and reassemble the fittings several times.

Special orders can also be supplied from Hastelloy, Titanium and other highly alloyed materials. Material certification to DIN ISO 10204; ANSI etc. is available on request. Specialised testing and approvals are also possible if required.

Like all other fittings of Schwer manufacture, the media-carrying parts are lasered with a test number that can be traced back to the source material with mechanical tests and the 3.1 certificate. From this number it is also possible to trace the fitting back to the production facility, the machine and the employee who manufactured the parts.

Further Information is available at

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