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    The problem I am going to address in this article is related to re-commission of hydraulic systems, powered by diesel engines with mechanical fuel injection pumps. Sadly, mechanical fuel injectors are becoming history, each day giving more floor to the modern electronics, but there are still quite a few of those diesels toiling in the field, and if you are a hydraulic technician, there is a good chance that at some point of your career you will deal with hydraulics of such an "old-timer-mobile", and, consequently, can get involved in the following re-commission. This post is, therefore, a "heads-up" to those who don't know it yet - old diesel engines can be much easier to start then to stop!

    There is no doubt that electronic injection is more efficient in transforming fuel into useful work, but the main advantage of mechanical fuel injection - its quality of being able to withstand all sorts of stresses and harsh environments - made these engines everlasting. I've seen ones with as much as 30,000 hours on their shoulders and still working! Being purely mechanical devices, they require no electricity to operate, and there lies their strength and their weakness - because in some rare cases, mostly due to malfunctions in stopping mechanisms, these engines can be very hard to stop once they've started turning, which can be a pickle when you have a large hydraulic pump coupled directly to the output shaft and you are the one responsible for putting the hydraulics back in service.

    When you reinstall hydraulic components, especially in large and complex hydraulic systems, with so many oil lines being reconnected, it is not uncommon to exist oil leaks, loose ends or even bad connections, which can cause all sorts of troubles and even unwanted movements as soon as the engine is started. Even during well planned start-ups there are hundreds of things that can go wrong and require immediate engine stop - that is why it is extremely important to make sure that you know how to STOP the diesel before you start it. I am telling you this because stopping a mechanically injected diesel engine can get much trickier than turning a key or pushing a button.

    Naturally, in case of a more or less regularly maintained equipment, not being able to stop the engine you've just started will hardly be an issue, but I have seen enough to warn you about a possibility of such situations, which can have disastrous consequences.

     Imagine - the engine has started, and it turns out that a pressure hose was left loose at one end by mistake. The oil is streaming all over the machine, and since the machine is an antique, the windows shielding the operator's space are missing and the operator gets a jet of hydraulic oil directly in the face and runs away screaming "My eyes!!! My beautiful eyes!!!!" There's only you left, alone with the diesel beast... You rush to turn the ignition key, but the engine doesn't stop... Oups... Now where's that damned decompressor cord? Trying to cover yourself from the oil rain with one hand, you pull on the first cord your hand can grab, which turns out to be an outdated yet extremely powerful pneumatic horn... There are no windows to protect you from the blast and you feel every one of those 160 decibels try to set your hair on fire... Despite being dazzled by the horn and blinded by the hydraulic oil, you are still heroically trying to stop the mechanical monster and pull something else real hard, ending up with a broken lever in your hand... The sound of the engine revving up tells you that you pulled the throttle... As you try to bail out of the operator's cabin, you slip on the oily floor and stop yourself from falling by grabbing on another closest thing within your reach - the joystick (with one hand, as you are still holding the broken lever in the other hand) setting something heavy in motion, most probably the boom rotation. As the boom rotates you are thrown out of the cabin by the centrifugal force. While you are flying through the oil mist, you hear the boom hit something and the operator's cries come to a sudden stop...

    The situation I fantasized above is based on a REAL LIFE ACCIDENT, and is only slightly exaggerated...

    Just a week ago I was asked to assist a start up of a rebuilt hydrostatic transmission, which was mounted on a very old  front loader, powered by a two cylinder air cooled diesel engine, which once started, only stopped when the injector line connections were untightened. The transmission had a badly adjusted null, and the loader began creeping, which caused a couple of extra agitated moments, as all the attempts to stop the engine "by the book" failed. (By the way, a small video of this machine will be used as an example of correct null adjustment technique and will be included in the second part of the "Finding Zero" series, which is due this month).

    Allow me to add another industrial tale. A client of ours had the diesel engine of his O&K excavator completely rebuilt. The motor stopping system was not original and consisted of a small pneumatic cylinder that closed the fuel valve. The valve did have a manual override, but it "wasn't there"... The first time the engine started after the rebild, one of the two screw-on engine oil filters was blown away by the oil pressure (later it turned out that the pressure limiting valve had been assembled incorrectly) and the engine lost oil pressure (and the oil as well). The pneumatic "invention" didn't work as there was no air pressure in the system yet, so the engine worked DRY for around five minutes before the operator came up with an "alternative" stopping solution - all too late. The motor had to be rebuilt one more time... Since then a piece of wire was attached to the valve rod, with the other end hanging loose from one of the sides. Although doubtfully aesthetic, it was a functional secondary engine stopping solution, which is in service till today...

     When dealing with putting back in service old machinery, powered by mechanically injected diesel engines, you should always take some extra care to check if the engine stopping system is in working condition.  Even when there is an operator present, it wouldn't hurt to take a minute to inspect the engine and define where the fuel injecting pump is and if there is an alternative to manually cut the fuel supply or pull the decompressor cord/rod/whatever... Don't start these engines unless you are sure you can stop them.

     Here's a couple of hints:

Diesel engines can be stopped by

a - cutting fuel supply
b - cutting air supply (or, alternatively, directing a CO2 fire extinguisher into the air inlet to smother the engine)
c - operating decompressor (when equipped with one)
d - stalling the engine (on systems equipped with fixed displacement pumps it is often possible to stop the engine at idle by extending one of the cylinders till it reaches the end of stroke)

    Re-commission of hydraulic equipment often brings surprises that aren't directly hydraulics related, like the described diesel stop problem. Being prepared for them is what differs a great hydraulics technician from a good one.

An Add-on to this post, featuring another amusing intustrial tale, was published on 29 June, 2011