Originally Posted by mick15

Having read these endless threads regarding Festo and negative pressure I carried out out some physical tests requiring the disassembly of a number of 4mm fittings. Here are my findings hoping to clear up this issue (though I doubt it lol)

All of the 4mm "small" fittings use an "0" ring of Festo design. This ring is of flat design containing a moulded in o ring this design makes the fitting of the tube easy as the tube enters the flat part of the seal then the extra pressure engages the tube into the o ring portion. This fitting is able to sustain leak free use in both positive and negative pressure.

The second type of 4mm fitting is slightly larger and has a different feel when fitting your tubing, the reason for this is simply the seals are of the "lip" design, and are totally unsuitable for the suction side of any application.

m