This story is about a "hydraulic malfunction" of a split barge (the very one that I mentioned in the article on oil spills).
For those of you who don't know - split barges are used to transport dredged materials and they are called "split" because they have a longitudinally split hull, hinged at the deck level, which can split open to dump the load. The mechanics of that particular barge was of the simplest kind - two hinges, two massive hydraulic cylinders, and an elementary hydraulic circuit that consisted of a gear pump, a lever operated DCV, and an over-center valve - not more not less (don't mind the missing relief valve, the diagram was made in a hurry):
So, one day I was asked to assist with an apparently simple problem - the barge wouldn't close completely on one side, leaving a good three-inch gap in the bottom, and since it was being used for dredging sludge - even such a narrow opening allowed a lot of material to escape. The owner and the crew were convinced that it was a hydraulic problem, that could be solved by simple adjustments (if they, naturally, were to be performed by a skilled enough professional).
The barge was working in Southern Spain at that time - quite a long way from Lisbon, so it took me good five hours to get to it. The hydraulic cylinders were submerged, but it was apparent that the split hull was lacking a couple of inches to close at the stern.
Surprisingly, it was hard to determine when exactly the malfunction had appeared. I was told that not so long ago the thirty-year-old hull had undergone major repairs with many steel panels replaced and re-welded, and there were even a couple of crew members who kind of recalled that the hull didn't close "right" the first time the barge hit the water after the overhaul, but for some reason, nobody could tell for sure. Since then the barge had been transporting rocks and boulders, so the narrow gap made no difference till the day they had to haul sludge.
A quick check of the hydraulic system revealed no malfunctions. It was a very simple circuit, and it was working at relatively low pressure - around 150 bar, which was more than enough to close the hull and keep it closed when loaded. I opened and closed the barge a couple of times, and the hydraulic system was working flawlessly. I measured the pressures in the cylinder lines to make sure that there was no back pressure - it was all OK, so I called the captain, showed him the readings, and explained to him that the problem was not being caused by the hydraulic circuit but was "mechanical", meaning that something was jamming the movement. The way I saw it there were several possibilities:
a) There was a malfunction inside the hydraulic cylinder that wasn't letting it close completely (like a loose piston nut)
b) There was a foreign object below the water line that was jamming the hull
c) There was an excessive wear/play in the pivot points - i.e. the cylinder eyes and pivot pins or the hull hinges
d) The whole hull structure was "crooked"
I also informed him that no matter what I did with the adjustments I wouldn't be able to solve the problem.
The crew members told me that the first thing they did after noticing the partially opened hull was inspect it for foreign objects - and none were found. The crooked hull theory was discarded as impossible, even though some "circumstantial" evidence and "unofficial rumors" stated that the malfunction was already present when the boat left the shipyard. In any case, it turned out that despite the very extensive repairs of the hull, the two enormous cylinders weren't serviced, in fact, even the hydraulic hoses (that were in an extremely deteriorated condition) weren't replaced. So it was assumed that the problem was most likely "cylinder related". Since there was nothing else I could do, I headed back to Lisbon. The repair of the cylinders was scheduled for the next pit stop, and the problem got temporarily solved by landing the dredge over a shallow beach during a low tide and then welding a steel stripe to cover the gap:
A year passed, and we were contacted by the same client over the same matter - the "open hull problem" remained even after repairing the cylinders. Just as before, the owner, the skipper and the crew were convinced that the problem was being caused by the hydraulic system. This time the barge was working on the Tagus river not far from our shop, so I didn't have to drive for more than thirty minutes to get there. Once again I made all the tests, and once again I came to the same conclusion - the problem was mechanical and not hydraulic. I did all I could to convince the "audience", but still nobody was believing my conclusions.
For a more detailed inspection, the skipper managed to strand the dredge on a sand stripe in the middle of the Tagus during the low tide. This is the place where I tell you that one very good thing about this job is that you often find yourself in pretty cool scenarios - for example - I took this picture standing in the middle of the Tagus river, in the spot that would be eight feet underwater in a couple of hours (and I got to ride on a cool tiny motorboat!):
Anyhow, we (once again) inspected the closing gap for foreign objects - and (once again) none were found.
Since the temporary steel stripes could work as a jamming point they were removed - and still, the barge wasn't closing. The cylinders were accessible now:
With an enormous effort and a lot of ingenuity and help from the sailors I managed to disengage the front pin and suspend the "malfunctioning" cylinder - and of course now when the rod end got pressurized the rod went back for another couple of inches.
I was sure that all the doubts were cleared, and yet the owner still wasn't believing that the barge couldn't close for other than hydraulics-related reasons. He kept telling me that it was impossible and I kept telling him that it was impossible, with my "it" being the complete opposite of his "it". It was a classic standoff - but I had one last ace down my sleeve...
The "ace" was "retreating and coming back with reinforcements". I made a sad face and admitted that I, naturally, could only draw my conclusions based on my personal and very limited experience, and of course, I could be mistaken. But what I could do was bring along a much more experienced and much better titled "second opinion", that would surely clear all the doubts.
"Fear not" - said I - "for the next time I am back, I shall bring along the engineer of engineers, the man of boundless erudition and colossal experience, the man who once stopped a train with a calculator and who shines his shoes with an angle grinder... He will come and he will heal the cursed vessel, and then she will close, my friends, CLOSE I tell you! And she will dredge like she never dredged before!"
On the next day, a colleague of mine came along and we took a nice boat ride to the barge, stranded in the middle of the Tagus. My colleague, unlike myself, carried along the two "big guns" that never fail - an awe-inspiring mechanincal engineer's title and a respectable middle-aged appearance. When the man inspected the system and repeated the same opinion I'd been trying to sell for the previous three days, most of the crew got convinced it was true, and yet the owner was still somewhat unsure - "it must be the oil pressure or something..." - the man kept saying.
At that point it was no longer a troubleshooting event, it was a "find a way to convince this fellow" affair. In the last attempt to prove our point we voiced an ingenious plan: "OK, say your hydraulics does lack pressure - what if we bring over a power pack, capable of reaching much higher pressures, and connect it directly to the malfunctioning cylinder, thus eliminating the existing circuit? And then raise the pressure to a much higher level than the normal working one?" The owner thought a little about it - and then gave it a go.
We brought a new power pack onboard, and connected it to the rod end of the "malfunctioning" cylinder, while the other end was intentionally left open to show that there was only the atmospheric pressure in the cap end (and also to check for any internal leakage).
I turned the power pack on - and the dredge was still not closing. I raised the pressure to 150 bar - nothing, 200 bar - nothing, 250 bar - still nothing, at this point I told the owner: "Look, you have a simple cylinder (no anti-drop valves inside) that has 250 bar in the rod end, and zero bar in the cap end, no internal leakage - since no oil was coming out of the open cap end connection, and we know for a fact that the rod can move for another good two inches - which means that at this point the cylinder is not closing because the structure is not letting him close. Why? Don't know really, but since no foreign objects jamming the hull were found, the only explanation I could find was that the complete hull structure was crooked in relation to the hinge axis, and the closed bow was in fact the mechanical stop. The boxed construction of the hull made of reinforced steel was stiff enough not to bend even under the enormous force of the cylinder. Then I added that if he wanted to continue with the experience, it would have to be done at his own risk, since without having any hard data about the cylinder walls we could be already passing the safe pressure level - the owner reflected for a minute, and then said: "no need, take the hoses out, connect the system back the way it was - we'll have to continue working the way we were..." Alleluia! Finally, our point was proved... Although I was kind of hoping the man would want to go for "more radical" pressures - to see if we could "straighten the crooked dredge out"...
Now, what can be learned from here? Psychology, my friends, it's all about psychology - we troubleshoot machines, but we deal with the people behind them - never forget about it! No matter what we do, there will always be those who judge a book by its cover and a technician by the amount of Grey hair, so instead of flipping on the "stress mode" we'd best learn how to live with and find our way around it!