All of us, everyday hydraulic lads and lasses, every once in a while come across individuals that have no experience in hydraulics but are forced to perform a "hydraulics-related" task. Either because they were told so by the boss, or they thought it would be easy and decided to give it a try, or maybe the regular hydraulics guy got sick and "someone just had to do it" - it doesn't matter... What matters is the unpredictable outcome of such "inexperienced" interventions, when people take obvious things, and interpret them in the most screwy ways, bringing a smile to our experienced faces, and occasionally leading to a spectacular disaster...
Six years ago I was involved in the commissioning of a brand new fishing ship's hydraulic system. As usual, the steel piping had been installed during the initial construction stage by shipyard welders and fitters, who knew everything about welding and bending pipes, but, as we were about to discover, knew very little about basic hydraulic components.
Normally, main hydraulic circuits on such ships have two sets of similar pumps, allowing both main and auxiliary engine operation. Very often open circuit pumps from the main and the auxiliary engines are connected to the same circuit via check valves - a nice and cheap solution to prevent backflow through the not working pump. What can be simpler and more obvious than that?
The in-line check valves had been installed by the same crew that'd done the piping. All of the lines had been painted with at least four coats of paint, so it was even hard to tell where the check valves were, let alone to verify their correct orientation. Besides that, the pipes were passing mostly under the metal floor, so there wasn't much of the piping you could actually see and access to confirm if the connections were correct. Anyhow, the piping was the shipyard's responsibility and guaranteed to have been mounted in accordance with the hydraulic schematics. Our job was to make the necessary hose connections and assist the start-up. By the way, that ship's engine room had an unusually low ceiling height - no more than a meter and a half - which made moving around a literal neck-breaking challenge...
The hydraulic circuit was very simple - an oil tank, two (huge) vane pumps, one on the main and one on the auxiliary, two check valves, one manual directional control valve, and one return filter. The pressure line connecting the main pump to the piping was a two-meter 1.1/2 inch 4SH hose with a nominal working pressure of 300 bar, which was more than enough for this system. Everything was set, the fittings were tightened, the tank was filled, and the engine room cleared (as you can imagine, along with ours, other technical crews were working all over the ship finishing the build - welders, electricians, painters, you name it). Only one courageous electrician, who was working right next to us, and who had been repeatedly advised to leave the machine room "just in case" as we were about to "unleash the beast", preferred to stay and watch. I signaled the engineer to start the party.
The main engine (twelve-cylinder diesel, around 10 liters (610 cubic inches) per cylinder, noisy as hell, too) started "pok-pok-pok-pok", as any decent diesel would, and I nodded to the engineer to engage the clutch. The clutch made a click, for a second or two nothing happened, and then there was that huge gunshot BOOM, the 4SH hose split open in the middle, lashing the electrician with a burst end (broken wires sticking out and everything) along the leg, and fountaining oil all over the tight engine room... I wasn't happy, oh no I wasn't... (By the way - it was the first time I saw a brand new hose burst like this - right in the middle - normally it happens at one of the crimped ends).
Of course, the check valve had been mounted "the other way round". Later I found out that the person, responsible for the installation of the check valve, misread the marking on the valve's body. The check valve was clearly marked with a standard ISO check valve symbol, you know, the seat and ball one, which he misinterpreted as an arrow, pointing the wrong way!.. There ARE in-line check valves on the market, which, indeed, are marked with an arrow, indicating the flow direction, but come on, there is a noticeable difference between an arrow and a seat and ball symbol.
Something, which is so obvious to us, can be quite misleading to others.
Another short example. My next-door neighbor (at that time) happened to be a welder. I bumped into him at our counter the other day inquiring about a gear pump. It turned out that a client of theirs, who had a small crane truck, had asked their shop to replace its worn-out pump. I helped the man to choose the right model and immediately forgot about it. Later the same day, as I was entering my apartment, I bumped into him again, and he said he was quite unhappy with our attending personnel, as through their fault he had to mount the pump twice. When I wondered why he told me that it was so because nobody had informed him that it was necessary to take out the plastic caps from the pump's inlet and outlet before the installation!!! I went speechless. I still don't know what to say to him, I really don't!
My point is - we sometimes forget that many things we, people who deal with hydraulics professionally, find obvious, aren't so obvious to others. That is why we must arm ourselves with tons of patience and a habit of double-checking everything, even, no, ESPECIALLY the most obvious stuff!
The poor electrician had to have his leg stitched and gained ample amounts of respect for hydraulics. He will be fine...