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    Very often I am asked about which is the best way to flush contaminated lines of a closed loop that suffered a serious failure. This article is a short description of one of the easy flushing techniques I've used for years, and that  hasn't let me down so far.

    Closed loops  are everywhere, and luckily for hydraulics businesses they break all the time, causing workshop owners to grin when a simple seal-kit pump overhaul is needed, to beam when a rotary group needs to be replaced, and to laugh heartily while rubbing (clapping) hands when a major failure causes a complete transmission to drop by. All the grinning, beaming and laughing is performed after the client has left the room, naturally...

    After a damaged closed loop pump or motor is repaired and re-installed on the machine, a special care must be given to circuit cleanliness and in particular to the loop lines, to guarantee that the recently rebuilt unit doesn't "expire" the moment it starts turning. This is especially vital in case of a major failure caused interventions, because the loop lines get contaminated with all sorts of debris, that can destroy the new transmission in a matter of minutes unless removed from the circuit.

    When the loop is simple and the hoses are short and easy to dismount, a mechanical cleaning (brushes, air projectiles, solvents, etc...) is an easy way to get rid of the contaminants, but when the lines are extensive and the circuit is more complex, it may be next to impossible to dismount and clean all the hoses, and in this case a flushing of the loop is mandatory before putting the machine back in service. There are various ways to perform this procedure, and in some rare cases special equipment is required, however most of the times the following simple technique (aided, of course, by others re-commission must-dos and could-dos, like mechanical cleaning, filter and oil change/analysis and common sense application) is enough to ensure safe start-up of a closed loop.

    The technique resumes to inserting pressure filters in the loop and using the pump itself to provide the flushing flow (along with actuator bypassing), which is exactly what you can see on these pictures, that demonstrate the flushing procedure being performed on a Parker RT 16 jaw crusher - a beautiful and intimidating piece of machinery, equipped with two closed loops that can work independently to pull on the caterpillars, or in conjunction to spin the crusher motor.

     The filter assembly, consisting of a pressure filter, a check-valve and a relief valve is introduced into the loop as close to the pump as possible, ideally - connected directly to the pump with a previously cleaned hose. The purpose is to filter the oil that enters the pump after flushing through the loop. The check valve guarantees unidirectional flow - through filter to pump, and the relief valve makes sure the filter/hose/check-valve isn't blown away in case the pump  pumps in the wrong direction, and is also a good "dude, it's the other way round!!!" indicator. Here you can see two filter assemblies (one for each pump, the relief valve tank hoses aren't connected yet). You can also see the traction motors and the crusher motor bypasses.

    A quarter of an hour of full speed operation at maximum displacement in both directions for traction and crusher circuits was enough to catch most of the garbage (note that when the flushing flow direction is changed, the filter position must also be changed, although for many circuits simple one side flushing is enough, not in this case though). The hoses were re-connected and the crusher has worked ever since...

    As you can see, this flushing technique doesn't require much gear (compared to an external power flushing cart, for example), and is relatively simple to apply.  It does have limitations, but is still a good and relatively cheap way to assure healthy start-up for the majority of  rebuilt closed loop transmissions. I applied it countless times and always got positive results.

   P.S.  Once I got the crusher moving, I couldn't resist the temptation of putting random everyday objects in the path of the 50 ton critter.... Another child dream come true...
Parker RT16 Jaw Crusher
Closed loop pumps
Pressure filters
Caterpillar motor bypass
Caterpillar motor bypass
Crusher motor bypass
Filter element
Filter element