Insane Hydraulics
Bold and audacious blog about fluid power
Due to our location and our main area of expertise - oil hydraulics - our main clients are all related to mining industry, and mining industry couldn't care less about such things as weekends and holidays. Take Fridays, for example. Fridays are universally the best days of the week, yet for us they have been most "action-prone" for some reason. Maybe it's my subjectively negative perception of any kind of unexpected endeavor on the verge of enjoying a weekend, but it truly feels like 90 percent of our "mine crises" take place on Fridays. Go figure...
Anyhow - back to the story. My phone rings, on a Friday afternoon, of course, and as I look at the caller id and recognize the mine's office number, the already well-established "telepathic" dance takes place: I stiffen my lips and raise the phone to show the screen to missus, which means "I'm sorry, baby, but it looks like it's going to be one of them long weeks again..", and she looks me in the eye while shrugging her shoulders and raising one brow - "well, we both know what has to happen" - and then nods her head in silent consent, which means "...relax and go do what you do best...". And then I answer the call.
That time an Atlas Copco dumper suffered a catastrophic pump failure, and since its only twin brother was already lying on the operating table waiting for a diesel heart transplant, most of the ore hauling process came to a grinding halt. To make things worse there was no spare pump available in the mine warehouse, and so, naturally, the only "one man A-team" in the area had to be summoned to the rescue.
In truth, a part of me was happy, because whenever I hear the words "urgent" and "catastrophic failure" together, I see two things - an interesting challenge and a bunch of dollar signs. I am always up for a challenge, and will do all that's possible to make "departed" hydraulics come back from the dead, but I'm also not ashamed to issue a proper bill for services rendered, since it's my responsibility to make sure this shop stays in business.
The "star" turned out to be a Parker P3 145cc open loop pump, which started with the shaft bearing failure and ended up exploding inside, scrapping the rotary group and the swash mechanism, while filling the circuit with all sorts of metal shavings, scrapings, chips, bits, chunks and fragments. We happened to have an almost exact same model in our Lisbon stock, with a different shaft - but the old one was in "reusable" condition, albeit heavily worn-out in the seal area, - so I was a happy camper rubbing his hands together! The shaft replacement in this pump model was a straightforward procedure that didn't require any major disassembly - which basically meant the weekend was at least partially saved.
I made the call. A colleague from our Lisbon office was handed the keys to the fastest available car with instructions to ignore red lights, stop signs and police sirens, and two hours and a hundred and fifty miles later the new unit was crossing over our doorstep. You should have seen me - I had everything on hand when the pump was brought in. Like a true professional! The parts clean and ready, the right tools lying orderly on the support bench like surgical scalpels in the operating room... All I had to do was remove the shaft from the new unit, pull out the bearing and remount it on the old shaft, install the old shaft in the new unit, put the seal cover back into place and - pronto! - good as new and pretty as a picture!
On such "missions" time factor is always the biggest priority. Normally, while you are busy repairing a pump, there's already a crew of mechanics doing all necessary preparations on the broken machine, a crew of production managers breathing down your neck, and a crew of supervisors filling out reports in order to attribute responsibilities. So I conducted the fix as fast as I could, and that very night took the pump to the mine where I proudly handed it over to the night-shift mechanic. I even came back on Saturday morning to assist the start-up and make sure everything worked ok. The pump, naturally, behaved like a champ!
To resume - a hefty sale, a happy client and a (mostly) saved weekend - not bad for a night's job. I think I was whistling that day while I was driving home...
When such predicaments happen, you don't worry about cleaning your work bench after the repair is finished, you worry about getting the pump to the client as fast as possible, and leave the shop cleaning for the next day.
So, I come back on Monday, check my emails, change into the overalls, and start cleaning my work bench. This goes here, that goes there, and.. Lo! Where did this retaining ring come from, I wonder? I, naturally, think - it must be from the old pump - so I hastily take the bashed pump parts out of the box - and, lo again! Another retaining ring of the same size! And then it strikes me, as the complete repair process flashes in front of my eyes in a matter of a millisecond - "You forgot to mount the bearing circlip, you moron!"
Allow me to explain, if you don't see what I mean. In this pump model there is a circlip that secures the shaft bearing in place, and another one above the shaft seal cover - check out the exploded view, and also this picture, which shows the groove where the missing circlip was supposed to be placed.
Yep - I really did it that time. For a brief moment I clung to the thought that maybe, just maybe, it wouldn't matter much, since the spring inside the cylinder block would naturally push the bearing towards the seal cover, and then the outer race would rest on the seal cover and the unit would end up with just a slightly smaller mechanical pre-load of the cylinder block, which wouldn't matter much, taking into account the fact that apparently the lower pre-loading wasn't influencing anything during operation.
All I needed to check my "theory" was a shaft with a bearing and a seal cover. I did have the cover, and I did have the shaft left from the new pump, but I didn't have the bearing. Some sort of divine intervention, however, made me double check our stocks - and it turned out we did have a new shaft assembly (with bearing!), as it had just arrived! I'll never believe in coincidences aver again! I picked up the shaft seal cover from the scrap, the new shaft assembly from the shelf, and stacked them together to see where exactly the bearing ended up. Well, much to my dismay, it turned out that removing the circlip that holds the outer race of the shaft bearing in place and letting it move forward (which is exactly what happens inside the pump since the barrel spring is pushing the shaft outwards) will result in the bearing stopping when its polymer separator hits the narrow protruding rim of the seal cover!
You heard me right! - The cylinder block loading spring plus the case pressure were pushing the pump shaft out, creating an axial load of at least several tens of kilograms, and the shaft bearing, instead of supporting the load on its race, was supporting it on its polymer cage sliding over a slim circular strip of steel at 2000 rpm for at least 16 hours every day. Let me say it again - on its freaking cage, whose main function's to keep them rollers symmetrically separated and pretty much nothing else.
I have a very strict policy for whenever I screw up - I come clean a.s.a.p. But man, it was one of the hardest phone calls that I ever had to make. Thousands of pumps and motors overhauled over the last ten plus years - yet all this experience didn't count for squat when I left the darned circlip out! It's like remembering to wear the belt while forgetting to put on the pants! Professional my left nut!!!
Anyway, I pick up the phone, call the guy in charge, and in a remarkably diplomatic manner tell him that a bearing retaining ring in missing in their brand new pump because I screwed up the mounting procedure, and now there's a real chance that something very unexpected will happen unless we do something about it, in other words - stop the loader as soon as possible and let me re-overhaul the pump. To soften the blow I offered to replace the old, worn-out in the seal area shaft with a new one free of charge. I said what I had to say, and listened to what I had to listen, and that was that...
The thing about them mines is - you can't simply press a button and take a large dumper out of production. You have to wait till the department lets you, or till something breaks. So, for the sake of avoiding permanent indisposition, I did my best to reprogram my mind into considering this whole quandary a daring experiment, conceived and realized by an audacious and handsome technician, in order to once and for all answer the question if polymer cages of roller bearings could be axially loaded... The "experiment" lasted for four(!) weeks, and finally ended when I got the call giving me the green light to re-repair the pump.
The pump is before me, let the drum roll begin! With a camera in one hand and a tool in the other, ready to objectively document whatever that's about to come out, I pry the front cover out with a trembling hand and... No visible damage to the bearing, no damage to the separator, and although you can definitely tell by the polished brim that the separator and the front cover were touching, the overall picture was - how do I put it - at least reassuring. Closer inspection did reveal some marks on the rollers, but not much anything else. Ok then, I'll take it! New shaft plus new bearing in, then a new shaft seal for good measure - and - the deed is done!
Here's the detailed "disassembly reportage":
The pump's waiting.
The front circlips´s removed
I am lifting the cover!
The cover's out and you can see that indeed the circlip's missing.
Here and here you can see where the separator was sliding.
The marks on the bearing rollers.
And, finally, you can clearly see me mounting a new shaft without forgetting about the circlip.
It's been half a year now, give or take, the pump's still pumping problem free for three shifts a day, so I am confident this one's behind me.
The new shaft that I got was a 16 series design, which uses straight roller bearing. Older series used double row spherical roller bearings, for some reason, but 16 design changes later Parker-neers finally started to use straight roller bearings like "normal" people. Don't bother looking for a new KOYO bearing with the reference number TJ-606-531. You probably won't find it - I didn't, at least in this part of Europe. Although Parker will gladly sell you a complete shaft assembly should you fancy one. This picture, however, can provide you with a clue on what you can do should you ever want to replace the original bearing without replacing the shaft.
What a relief, friends! What a relief!
At least we know now that it is kind of possible to apply an axial load on a polymer separator of a roller bearing for 4 weeks without breaking it. What a noteworthy piece of empirical knowledge, don't you agree?