Insane Hydraulics
Bold and audacious blog about fluid power
I got tricked by a bad hydraulic hose today - and from now on, I am adding an extra step to my hose-making routine. Let me share what happened, and you decide for yourself if I am being paranoid or not...
Our over-the-counter operation is tiny, so I don't make that many high-pressure hoses - I'd say a hundred-plus assemblies a month on average, give or take. Of all types and sizes, of course. The assembly of hydraulic hoses was one of the first skills I learned when I got my job as a shop hand, and since I have never had a helper myself - I "have been crimping my own hoses" ever since. At least when a hose fails, I know for sure whom to blame! My point is - I manufactured enough hoses to consider myself a "reasonably professional hose assembler," and I know which corners can be cut and which can not.
Like everybody else, we stock multiple brands, and our go-to choice for many years has been the combination of Intertraco fittings and Parker and/or Intertraco hoses. Quality stuff. Time-proven, too. I've tried many hose and fitting brands, both well-known and totally random, and there are definitely names I wouldn't want to see in my machine even if somebody offered them for free, but I've always had superb experience with Parker hoses and the Intertraco's two-piece fitting range - namely the type "B" hose-tails coupled to their skive and no-skive ferrules.
So, have a look at this freshly-crimped hose end (I realize now that I probably should have taken a picture of the complete hose before I cut into it - but it's too late for that now):
This would be the Parker 731-20 EN 856-4SH hose, assembled with Intertraco B-type hose-tails and S0420 ferrules that require external skiving. Looks good, doesn't it? The crimping diameter is 48.1 mm - and if you look at the crimping chart from 2009, and the one from 2017 - both of which give the crimping diameters for the 4SH hose/B+S0420 combinations - you'll see that the 48.0-48.1 is perfectly fine. I've assembled thousands of hoses just like that, and yet this particular one is a total failure! And no - this is not a bad assembly, and I'll prove it in a minute. So - if you peek inside the fitting with a flashlight - you'll notice something "fishy" at the bottom of the hose-tail:
That does not look right at all, does it? So, let us chop the ends off and take a closer look:
Yikes! Just looking at that hurts! Can you imagine how entertaining (among other things) would be to apply such a hose on "something earth-moving?"
Along with skive ferrules, I also use (and, in fact, give preference to) no-skive ferrules - Intertraco ref. S312T (crimping chart for EN 856-4SH here). Let us have a look at how one of these fares with the same hose (crimped to 51.5 mm):
This one didn't quite bite through the inner tube but still detached the tube from the wires! Maybe the oil pressure would "iron" those blisters out, and the hose would not leak, but I wouldn't risk it. So - the crimping diameters are OK, and the swaging head is true - meaning that it crimps a cylinder and not a cone. What else could it be? Maybe I forgot to skive the hose, or maybe I didn't insert it all the way? Let us cut the ferrules open and check, shall we?:
As you can see, the hose that had to be skived was skived, the hoses in both ferrule types were inserted all the way, and in both cases, the ferrules bit correctly into the wires - you can tell by the markings that the spirals left on the biting edges (or whatever the correct term might be). Here you can see a new hosetail next to the crimped ones - the new one is on the left, the skived one in the middle, and the no-skive on the right. The diameters did reduce after crimping (which is normal) - but since I don't have a "no-go internal diameter after crimping chart" for these, I can't affirm that they are "officially OK". All I can say is that they are as they always get - and thousands of hoses that I made and delivered problem-free kind of prove they are OK. On a side note - getting the crimping charts from Intertraco is a complete mystery to me because every single catalog page states: "Please refer to our crimping chart for more detailed application data" - and yet, for some reason, they don't have an official source where you can download that information - so you either scrub the web for it or "ask politely" in hopes that they provide you with one. I don't get it, Intertraco!
So, what happened then? In my opinion - for the first time in my life I got a bad hose. Most likely due to storage conditions. This particular roll must have sat in the sun for a long time, or at least that's what I imagine. I couldn't see, feel (even smell) any abnormalities, aside from, maybe, the slightly yellow-ish lettering on the layline, and the hose didn't feel any stiffer than usual. The cut looks perfectly normal, too:
Anyhow, I got our newest "good" high-pressure hose - namely the SR35-20, crimped it with no skive ferrules (and we use an even smaller diameter of 50.5 for this type because of its very thin, no-skive-ready skin) - and, as you can see, there's absolutely no "blistering":
So, first of all, from now on, this pen flashlight is a permanent add-on to my hose-making bench, and when I crimp a large high-pressure hose, I will always be checking how it looks inside after crimping (when possible):
Second - I'll get rid of all old high-pressure hose cuts and leftovers. Third - I would like to ask if "anyone in the audience" had a similar experience - if you did, please let me know.
P.S.
I'd like to add a few words on "floating crimping diameter recommendations", or at least that's what I call them. It is not uncommon for manufacturers to tweak their crimping charts "as the years go by". For example - Intertraco's charts for their 4ST+ hose with B-type insets and S312T ferrules from 2016 and 2021. You'll see that they "loosened" the -16 by 0.3 mm and "tightened" the -8 by 0.4 mm. I suppose this is OK, but I still wish they explained why they did it.