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    All of us, everyday hydraulic shop chums, once in a while happen to come across individuals who have no experience in hydraulics, but for some reason are forced to perform a "hydraulics related" task. Either they were told to by the boss, or they thought it would be easy and decided to give it a try, or the regular hydraulics guy got sick and "someone had to do it..." -  it doesn't really matter... What matters is the always unpredictable outcome of such "inexperienced" interventions, when people take obvious things, and interpret them in most screwy ways, often bringing smile to our experienced faces, and occasionally leading to a disaster or two...

     Six years ago I was involved in a start-up of a brand new fishing ship's hydraulics 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 back flow 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 pipes had been painted with at least four coats of paint, so it was even hard to tell where the check valves were. 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 to 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 distributor, and one return filter. The pressure line connecting the main pump to the piping was a two meter 1 1/2 inch R4 hose with nominal working pressure of 300 bars, which was more than enough for the task. Everything was set, the fittings were tightened, the tank was filled, the engine room cleared (as you can imagine, along with our crew, there were other technical crews 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 like hell) started pok-pok-pok-pok, like any decent diesel would, then I nodded 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 R4 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 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 on it turned out that the person, who'd installed 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 for us, can be quite misleading for others.

      Another short example. My next door neighbor happens to be a welder. I saw him at our counter the other day looking for a common gear pump. It turned out that a client of theirs, who had a small crane truck, had asked their shop to replace the 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 find obvious, aren't so obvious for others. That is why we must arm ourselves with tons of patience (for phone conversations) and a habit of double-checking everything, even, no, ESPECIALLY the  most obvious stuff!

    P.S.
The poor electrician had to have his leg stitched and gained ample amounts of respect for hydraulics... He will be fine...