Compression Fitting Question

[rock]

I was doing a little faucet plumbing last night and came upon a question that applies to hydraulic fittings. The water lines for the faucet I was working on were more like hydraulic lines (braided flex to stainless) than conventional poly water lines (Hans Grohe, the Germans don’t fool around).

I have attached a crude drawing to help with my question.

Figure 1 shows the fitting. The solid stainless end has a ridge. It is greatly exaggerated in the drawing; in reality the difference in diameters is only a few microns I suppose.

Is the brass ferrule for the compression fitting supposed to sit slightly on the ridge when the compression is made as shown in figure 2 (compression nut missing from drawing) or is it supposed to sit beyond the ridge as shown in figure 3. In the first case, when the compression nut is on, after initial compression it will be held on by the ferrule, which cannot slide beyond the ridge (figure 4), in the latter case it would appear that the ridge would be an indicator letting you know how far the fitting is sitting in its mate so that the ferrule is properly positioned.

In the first case not only is the ferrule held on by the ridge, the fitting (and hose) can’t slide backward from the compression nut and out of the fitting. However, my concern is that the only point of seal is right on the ridge.

In the latter case, the ferrule has more surface area to form a better seal, but the fitting might be more likely (might) to slide back out of the compression nut.

1) I’m not sure which of the two ways is proper.

2) Once you do the initial compression in the first case how do you remove the ferrule if you have to, now that it doesn’t want to slide beyond the ridge without damaging the surface area of the stainless fitting?

Thanks,

-- Rock

 

[bgott]

That ridge, if I'm reading you correctly, is formed when the fitting is first tightened. The force of compression shrinks the ferrule onto the pipe. File the ridge off and work the collapsed ferrule (sp?) off of the pipe. When you go to re-install a new ferrule put the nut on the pipe, the ferrule and then slide the pipe into the fitting until it stops. There should be a ledge inside the fitting that catches the pipe. Then tighten the compression nut. Sometimes you have to cut the ferrule and the section of pipe off and start with a fresh section of the pipe. HTH

I went back and looked at your picture again. You need to split the ferrule to get it off. I'd use a small cutoff wheel on a Dremel tool to cut it and try to spread it with a screw driver. Check for the ledge in the fitting, it's there for a positive stop. Did you have a leak at the fitting? I usually re-use the connection and hope like he11 it doesn't leak. If it leaks I junk the pipe and buy a braided hose with o- ring seals in it. I can get 'em to seal but I'm too durn old to screw around with it if I don't have to.

 

[rock]

Thanks for the reply. The ridge comes like that from the factory so the ferrule didn't make it. I can't imageine brass being able to do that to stainless.

Can't cut the ferrule and section of pipe like I'd do with copper, it would ruin the hose.

Great advice about pushing in the fitting until it stops. I'm going into a standard 3/8" compression under cabinet sink valve. That pretty much answers the question about were the ridge should lie. I think those clever Germans figured it all out for me.

I suspect I'll just have to really crank that baby down. It's not like copper where you have two pretty soft pieces going together, that stainless is hard!

Thanks,

-- Rock