Insert and ferrule 1/4" for Aquapro compression fitting ref. PR-INSERT-14

Insert and ferrule for 1/4" tube

Set of two translucent plastic parts designed for compression fittings on 1/4" tube:

• The insert: tubular sleeve with collar, which slides inside the tube end
• The ferrule: conical ring, which slides over the outside of the tube

Aquapro reference PR-INSERT-14.

The compression fitting principle

The compression fitting does not work like a push-fit quick connector. The seal does not come from an O-ring but from the deformation of the ferrule under the effect of tightening.

Assembly is carried out in this order, on the tube:

1. The nut is threaded onto the tube first, threads towards the end
2. The ferrule is threaded next, conical part towards the fitting
3. The insert is slid inside the tube, until its collar is flush
4. The tube is pushed fully into the fitting body, then the nut is tightened

When tightening, the nut pushes the ferrule into the conical seat of the fitting. The ferrule tightens onto the tube and provides the seal. The insert, placed inside, prevents the tube from being crushed under this pressure and maintains its circular cross-section.

The two parts are inseparable: without the insert, the tube crushes and leaks; without the ferrule, there is no seal.

Where this type of fitting is found

The compression fitting remains very common at points where the tube reaches the end of the line:

• point-of-use taps on reverse osmosis units, on the 1/4" outlet
• ball valves on pressure tanks
• certain reverse osmosis bodies and branded accessories
• domestic appliances connected with 1/4" fittings

Why it is a common spare part

The ferrule deforms on first tightening, permanently. Once compressed, it is marked by the tube section and the shape of the seat.

Consequences during maintenance:

• a tube removed and reassembled with the old ferrule often leaks
• a ferrule reused on a cut tube does not reseat correctly
• a ferrule tightened too hard is crushed and cannot be corrected by further tightening

This is why the insert and ferrule set is part of the service vehicle stock, just like O-rings. The cost of the part is negligible compared to the cost of a return visit for a leak under the sink.

Assembly

Cut the tube square with a tube cutter, without crushing or angled cuts. Respect the order nut, ferrule, insert before engaging the tube in the fitting.

Tighten by hand until contact, then tighten with a wrench on the flats, moderately. On a plastic ferrule, excessive tightening crushes it and destroys the seal instead of creating it.

Pressurise gradually and check the fitting dry by hand before closing the cover.

Good to know

This set does not replace a complete fitting: the nut and fitting body are not included.

Imperial 1/4" and metric 6 mm are not interchangeable. A 1/4" ferrule fitted on a 6 mm tube does not reseat the tube correctly.