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    I would like to start this post with a real life story I witnessed a couple of years ago.

    A client of ours - a dredging company - was claiming that the gear pumps we were supplying to them were of a bad quality, resulting in a very low durability - a couple of hundred hours at most, which, of course, was unacceptable. When confronted with the standard oil condition question, the owner of the business assured that the oil was "used but operational". It was obvious that the problem required investigation.

    The gear pump in question was used to power hydraulic jacks of a large split barge. A split barge is basically a barge that's "cut in the middle". The two halves are hinged at the deck and operated by two enormous hydraulic cylinders, the cargo (rocks, sand, soil) is carried in between the halves and is dumped by splitting the whole vessel longitudinally.

    Under normal working conditions the pump, run by a small three cylinder Deutz, worked for about fifteen minutes at most every couple of hours - the time to split and close the hull to dump the load. Operating pressure was relatively low, around 150 bar if I recall correctly, so the pump was working way below its rated capability.

    The inspection of the oil tank revealed milky smelly liquid, which the crew was persistently calling a hydraulic oil. A short conversation with the crew members revealed an astonishing and breathtaking tale about the unhappy day when a steal pipe that ran along the deck burst, spilling most of the oil over it. The main reason for the oil spill being so big was the fact that to stop the engine a manual decompressor had to be pulled, and the lever was mounted directly on the engine, situated in a small compartment under the deck - quite a long way from the cockpit. People, who never saw it, can't take their eyes from the dumping process, however those, who are already thick of seeing it on a daily basis, look everywhere BUT at the damping, so when the corroded pipe ruptured, nobody was looking at the deck, and when they finally saw the oil pool, the engineer had to sprint down several narrow stairs all the way to the motor compartment to stop it!

   The ruptured section was replaced, but the oil level in the tank was dangerously low...

   A flashback now, if I may - in the beginning of my hydraulics career I was employed at a company that manufactured hydraulic equipment for industrial fishing, and so I spent many days onboard  all sorts of vessels all over Portugal, which gave me the perfect opportunity to get acquainted with seamen first hand. One thing I must tell you - if a sailor (or a fisherman) can't find a way out of a pickle - the world has come to an end!

   That time was no different, and the crew quickly came out with an effective and elegant solution of gathering the spilled oil with brooms and shovels from the deck into buckets, and then transfer it from buckets back to the oil tank, filtering it through a piece of cloth... Of course, when you are facing a "no other exit" situation and you need the barge closed to navigate, I guess you might say "to hell with the pump, I want the damned barge closed", do the broom magic, come back to harbor, and deal with the situation there... But the thing is... the predicament had happened more than a year before!!! Ever since the incident the hydraulics has worked with the same deck-tainted oil! No wonder the poor pumps wouldn't last. I would guess half of the hydraulic oil was sea water, the other - sea-water-in-oil emulsion, with common deck-type anti-anti-wear abrasion additives...

    The most astonishing thing was the fact that neither the crew members, nor the owner of the business, were anxious about the oil. Their logic was bullet-proof - the water will eventually evaporate, the particles will eventually filter out, so no big fuss here... The sudden increase of pump failure rate was explained by low quality of the supplied pumps, and I'm still not one hundred percent sure that I managed to convince the owner that the hydraulic oil was no longer in an acceptable condition.

    This story is anecdotic, but I must tell you that I have seen more than once similar attitudes among hydraulics related businesses.  I am referring here, of course, to the matter of reusing spilled hydraulic oils.

    Oil hydraulics is all about oil in huge quantities, and it is normal that it gets spilled all the time - when you disassemble a component  - the oil is spilled over the bench, when you connect and disconnect a component to a test bench - the oil gets spilled, in fact, whenever you do anything around hydraulics - there's always an oil spill. Of course there are benches that are prepared to gather the oil spilled over them, and most of the times it is possible to catch the "runaway" oil from mounting/dismounting procedures into a tray, but there's still the question of what to do with it next.

   Simply discarding the gathered oil is only viable in case of very low volumes and occasional spills, but most hydraulic shops deal with oil spills on a daily basis, so throwing the oil away can become an expensive practice. Reusing the caught oil, by putting it directly back into a test rig or a machine is also a very bad idea, and, unfortunately, is something I see a lot in many shops out there. The main reason for it, is the fact that gathered spilled oil brings along huge amounts of particles washed from anything it was spilled over.

   With the oil prices constantly growing it is important and economically justified to reuse "caught" spills, but it is also very important to filter the gathered oil prior to reintroducing it to a hydraulic system. From my experience I can tell you that simple single passing  through a filter will not do the trick - the particle contamination level of  spilled/gathered oil is enormous (it is still better than simply pouring the oil directly to a machine, though), so it might not be an exaggeration to build a small tank with a filtering system for exhaustive filtering - which is especially important for pump test benches, where oil contamination levels should be as low as possible.

   As an alternative economic solution, a devoted spilled oil tank can be made, which, if designed properly, can use gravity to do all the necessary filtering. In that case I would suggest a high narrow tank (like a drum), with the suction line somewhere in the middle and turned downwards (probably with a screen), a ball valve and a bank of filters. When the drum is full, the ball valve is opened and the  oil is slowly drained from the middle, leaving all the heavy particles at the bottom, and most of the fine particles in the filters. The resulting oil can then be transferred to the respective machines/ test benches though their return filters using previously mounted fast couplings.

    It is also very important to make sure that there are no mixtures of incompatible oils. As a rule, you can mix different viscosity grade hydraulic oils with the same additive package without consequences, but when not certain, your best bet is still to discard the unknown oil.

    My point is very simple - it is not wise to simply throw away spilled oils, but it is also unwise to re-use them without prior filtering. Lots and lots of technical solutions are possible for that purpose, but it should be noted that simple one filter solution, though still better than none, will not give satisfactory oil cleanliness levels, therefore more elaborate filtering solutions should be applied, without leaving aside one of the best (and free) particle separating agents  - the gravity. In any case the priority should be the cleanliness level of the outcome oil, and not the filtering speed.