Insane Hydraulics
Bold and audacious blog about fluid power
Most of you already know that I deal primarily with mining equipment, and when it comes to technical assistance in an underground mine - take my word for it - the "ambiance" is... tolerably depressing. This is the best description I can come up with because when you mix the heat and the dust with hydraulic oil, and then "sprinkle" it with scarce illumination and lack of space, you get the perfect recipe for lowering even the highest of spirits. I like to think that I am used to this, and that my pain threshold is higher than average, but even so, I will always appreciate each and every second of a service call that is done in any location that's "not in the mine." These are rare in my current life, but still existent. Check out the dirt track I had to take to get to a job site this week:
A grand avenue of welcome, leading to a core drilling rig proudly standing in the middle of a beautiful Portuguese olive grove. How's that for a change of scenery?! But of course, I am not here to discuss spectacular landscapes, I am here to talk about hydraulic matters, and so, let me share with you the details of this service call, and then some thoughts that it provoked. Usually, I post good examples of bad examples, but this one is different - it is going to be a good example of a good example, which is a welcome change.
So, I got a call to troubleshoot a hydraulic malfunction on a core drilling rig I'd never seen before - an S15 from DBC Makina (a well-established Turkish manufacturer of drilling equipment). I was supplied with the hydraulic diagram, and I could also request more technical documentation if I needed it. But a hydraulic diagram was a good start - a quick look at it told me that the system was pretty much a clone of the Atlas Copco CS14, and when I saw the rig in the flesh, my suspicion was confirmed - same system, only some of the components were different. I actually liked what I saw - the rig seemed to be built pretty solidly. The malfunction itself is not that important for this context, but I will describe it briefly anyway, and I apologize for the absence of wide shots - I am at liberty to disclose only the close-ups.
The operators were complaining that the main hoist was dropping the drill string when the drilling head was moving down with an open chuck. I realize that this phrase makes little sense if you are not used to core drilling rigs, and I guess you will have to believe me when I say that this is not normal. The hoist is equipped with a negative brake and a pilot-activated freewheeling system which are unlocked when the pipe string is pulled down with a closed chuck (allowing the hoist to pay out the rope attached to the water swivel that sits at the top of the pipe string), but it should never freewheel when you move the drilling head with an open (i.e. pressurized) chuck, with the pipe string secured either by the rod holder at the bottom, or by the main hoist.
So, before anything else, I installed a pressure gauge in the negative brake line and confirmed that the hoist free-wheeling system was, indeed, being piloted - and that it would release at about 20 bar:
This is, by the way, me flexing (again) with my wireless pressure measuring system! I have the wireless pressure sensor attached to the brake release line, which is on the other side of the rig, and I am standing at the control panel and monitoring the pressure on my smartphone as I move the levers - super convenient. Honestly, I can't see how I could live without it.
Then I opened the panel and located the manifold with the valve responsible for venting the freewheeling pilot when the drilling chuck is open, and disassembled it to confirm that it was not stuck:
The Hydraforce cartridge valve was perfectly fine and was opening and closing properly, so the only two ways the pressure could rise so high with the valve open were
a) a blockage in the drain line, or
b) an excessive oil supply
When I disconnected the drain line, I saw a large stream of oil pour out because of the elevated tank, which meant that most likely there was no blockage there, and so I directed my attention to the supply - the line that ran through the frame of the rig all the way to the the end of the mast cylinder, where, according to the schematic, there was supposed to be a 1.6mm orifice somewhere. The diagram didn't explain exactly where the orifice was located, but since it was represented external to the valve manifold, I assumed that it would either be inserted in the fitting itself, or in an additional male x female adapter.
I quickly located the pilot line, removed it, and found no orifices anywhere, and the fitting looked pretty standard:
Luckily, there was another rig of the same make and model drilling near-by, and when I removed the same fitting from it I found this:
What looked like a normal -6 JIC fitting turned out to be an orifice (a good example of a fitting that can fool a hydraulic technician, by the way). Problem found! I returned to the shop and made a similar throttle from a standard fitting and an M8 grub screw:
And then I went back to the rig, installed the new piece, and boom - problem solved!
And now, my friends, let us talk about the very important point that this service call so nicely demonstrated - the unbelievable ease with which I was able to identify the key components and follow their connections on an unknown hydraulic system equipped with long and bundled flexible lines routed through a large frame. Let this sink in for a second - an unfamiliar hydraulic system with long and bundled flexible lines routed through a large frame.
Go back to a couple of paragraphs above and note the phrase - "...I quickly located the pilot line, removed it, and..." - and here's the respective image. There's a tag with a code on the hose end, and the same code is clearly marked next to the respective line in the hydraulic diagram, so it took me less than a minute to identify the line of interest. Now - imagine there were no tags...
So very often (too often for my liking) when I need to work on large systems built around custom valve manifolds and multiple flexible lines neatly tied together with an infinite amount of zip-ties and then routed through meters of impossible bends inside a (mostly inaccessible) frame - discovering "what goes where" becomes a nightmare, and I spend 90% of my time doing the annoying and frustrating hose-pulling exercise when me and, hopefully, a couple of helpers are trying to map the connections by vigorously yanking on hose segments on one side of the frame and seeing "what moves" on the other. I can feel the pain as I write about it!
On this rig, however, all the hoses were still original (the rig had some 4000 hours, if I am not mistaken) and every one had a coded tag on both ends:
And as I already said, all of the hose codes were conveniently included in the hydraulic schematic. This, my friends, is pure gold! There was no guessing from my part - all I needed to do was read the code on the tag, and I knew exactly what line I was working with. Having a properly made hydraulic schematici and properly marked hoses made all the difference in the world!
Yes - "navigating" through such a well-marked and documented system was super easy, but I can totally see how during the next major overhaul (or even a sporadic hose replacement) an old tagged hose goes into the bin, and a new and shiny, but un-tagged hose takes its place... And how, some years later, a hydraulic technician looks at this system and says something like: "I can't figure out sh## in this rats nest of hoses!"
So, if you are designing/building a hydraulic system that uses lots of bundled flexible lines routed through a frame, make sure that:
a) All hoses are tagged on both ends, preferably with codes that make sense (e.g. DR.. for drain lines, PP.. for pilot pressure lines, LS.. for load sensing lines, etc...) and
b) These codes are clearly mentioned next to the respective lines in the hydraulic diagram.
Most of the "big players" already do this, but smaller companies more often than not neglect this practice completely. If this is your case, I urge you to rethink this. Somewhere down the line, there will be a hydraulic technician either frustrated or utterly flabbergasted (in a good way) by your choice!
If you, like me, make and/or replace hydraulic hoses day in and day out, whenever you get an old hose sample with tags on it, make sure you find a way of transferring the tags onto the new hose, for the same reason.
And finally, when you diagnose a hydraulic system, and see that it has hose codes included in the diagram, check for the hose tags and don't forget to use them to your advantage - knowing the lines is a great way of identifying port function in unknown valve manifolds, which can be very handy.
I am so used to working on unmarked and undocumented hydraulic systems that seeing such an "engineering marvel" truly felt like a breeze of fresh air!