Insane Hydraulics
Bold and audacious blog about fluid power
If you are somehow involved in the business of hydraulic pump and motor overhauling, you probably already considered an "economic" spare parts supplier at some point, and most likely it felt tempting and scary at the same time. Well... It should feel scary because while you can increase your profit margins and provide a more competitive price by using aftermarket parts, you can also take a serious blow to your reputation and lose a bunch of clients over a series of bad overhauls caused by a low-quality spare.
So, in this post, I would like to give my take on non-original spare parts for hydraulic pumps and motors. Everything that I say comes from personal experience, and since I've been on "both sides of the overhauling business barricade" (the shop and the sales) for a long time, I think that my (arguably privileged) position grants me a point that is worth sharing.
Believe me when I tell you I've tried them all... Sigh... (I guess the sigh is due to the fact that I just realized that I've been doing this for longer than I care to admit). I still remember how we received our first "oriental" pump parts that looked as good as the original ones. Even better, actually, or at least shinier, and how the purchasing department went on a"buying spree" getting like ten barrels for the price of one... And then the first successful repairs. And then the breakdowns and warranty claims... Good times! Love and hate relationship in its purest form!
We, as mechanics, used to hate them "damned counterfeits". And no wonder - a mechanic, as a person who shoves the parts into pumps and motors, will always choose a genuine replacement part over an aftermarket one because OEM parts are easy to work with, they always fit, and they require no "finishing touches" - ergo his work is simpler and faster. A mechanic doesn't care about how much the parts cost because he's not the one paying for them. Genuine parts are hardly ever faulty, so the risk of having to re-open an overhauled unit - probably the worst thing that can happen to a mechanic - is minimal.
But our colleagues from the sales department, being "pure-blood" businessmen who directly profited from sales, loved the aftermarket parts! At least in the beginning... The parts cost a tiny fraction of the original price but could be charged as genuine, so - easy money! The buyers, obviously, never cared about the quality because they never touched the parts. What do I care if the swash plate does not fit or "looks funny"? File it down or something, lad, I am sure you'll figure it out!
It took us all some time to realize that the truth, as always, lies in the golden middle, and even more time to realize that the middle is, actually, very much closer to the "original expensive" than the "cheap aftermarket". All of our initial "Hurrahs" got replaced by "Boos", and since our policy has always been to never let a client pay for a breakdown caused by a low-quality part, quite a few lessons "learned the hard way" taught us that in most cases using Chinese spares in hydraulic pumps and motors is like using bathroom soap for filling cakes - looks and smells nice but tastes like... crap!
I used to think that even though most of the time you got what you paid for, this didn't mean that you couldn't get a bargain for a penny every once in a while, and I always said that a sound overhauler should keep his eyes and mind open and use both genuine and aftermarket parts in a combination defined by his trial and error experience and the pump/motor application demands.
This approach sounds reasonable, doesn't it? And it is true that even in pre-recession years we had hydraulic equipment owners who actually preferred aftermarket to genuine in the pursuit of cutting down overhaul expenses. So, since some clients want genuine quality, and some want a lower price - it seems that to satisfy both you should be able to serve both, right?
I used to think so, I did. I even said things like "If your goal is to deliver quality repairs, aftermarket part suppliers should be chosen with a cool head and based on quality, not price!" You know what we do now? We stopped using non-original parts unless we absolutely have to. For all major brands - Rexroth, Parker, Danfoss, and Eaton - we use the good stuff and never look the other way. Period. The only parts that I can cut costs on are the shaft bearings and, on some occasions, the seals - because I can get both faster and cheaper locally, but the rest either comes from the "right place" or there's no overhaul at all.
Why is that? In short - too much hassle with the cheap spares. There are hundreds of companies in China that will sell you spare parts for almost any existing brand, with the quality ranging from superb to unacceptable and even ridiculously unacceptable. However, with most suppliers (and especially resellers) the fact that you have received a batch of supreme-quality spares doesn't guarantee that you will get the same quality in the next batch. So it's simply not worth it.
OK, you say, so I am a hydraulic equipment owner, and I've got this excavator pump to repair, how do I know if I am going to be scammed with them Chinese spares? Well, there is no simple answer to this question...There is an opinion that if an overhaul is backed up by warranty then you're on the safe side, no matter what parts were used - this, unfortunately, is not entirely true, because if you're the unlucky hydraulic pump owner caught in the "error" stage of the new supplier trial and error validation process, you can get two different answers and two very different bills depending on how honest the company you are dealing with is.
An honest workshop will admit their fault and try to correct the mistake as fast as they can, and if you are not a first-time customer you might even get the - "Sorry about that, dude, the parts're all **cked up..." confession, while a less candid workshop will give you the standard "commission errors committed by non-qualified personnel plus hard particle contamination in conjunction with the inappropriate oil temperature and deficient system design" excuse, and make you pay for their poor part supplier choice. So I'd say that warranty alone isn't a guarantee and would cast my vote for warranty combined with transparency - if a workshop has good experience with their non-genuine spare parts supplier - they won't be ashamed to admit that some of the spare parts they use are not original.
I would still underline the importance of the brand though. There are a couple of pump brands that you can't get original spares for, especially in Europe, and so your only choice is the aftermarket - and I can understand this, but when you tell me that you have a "new and stellar" parts supplier for, say, the ubiquitous Rexroth A10VO lineup, I stop listening. Been there, done that, don't do it no more. And, hopefully, the following examples will make you see why.
Bimetallization is a complicated manufacturing process, that requires a lot of know-how. This type of failure is common for cheap aftermarket cylinder blocks - the bronze layer detaches during the first hours of operation at pressures often lower than nominal. Such barrels present no visible external deficiencies. I once saw a Sauer Danfoss series 90 aftermartket cylinder block "shoot through" the bronze layer at 300 bar during the first 30 seconds of the test run.
This useless piece of crap is supposed to be a swashplate for a Rexroth A4VG pump. Notice the ridiculously low-quality casting. The original swashplate is supposed to be one piece, this junk, however, is a two-piece invention fastened together with low-grade bolts. The steel used for the link was so incredibly soft that it became loose and the pin got ovalized in a matter of hours!
There is much more to casting iron than poring melted metal into molds. These examples show more swashplates for Rexroth A4VGs. The casting is of an extremely low quality, and presents a notorious hairlike pattern - the sign of poor bonding between the layers of melted metal. Bad casting, combined with inadequate heat treatment results in very fragile parts. Here you can see such a swashplate after 2 hours of operation - it already started to crack, and the last four pictures show how such a part can cause a catastrophic failure (again - after but a couple of hours of service).
This very good-looking and seemingly flawless copy of a valve plate for a Rexroth A6VM motor is useless - the curvature of the valve plate is not equal to that of the end plate! I marked the sealing surface and then rubbed the plate against the end plate to reveal the difference. As you can see, the only contact points are the extremities of the valve plate. The gap in the middle is 0.3 mm high - meaning - "rivers" of internal leakage! This valve-plate is so well finished, that a less experienced mechanic could easily mount it without noticing that it's faulty.
The copying industry can't keep up with the constant progress of Komatsu designs. The first picture shows an aftermarket barrel for the Komatsu HPV 112 pump - the "manufacturer" copied the external dimensions, but left out the patented stuff, like the uneven port pitch of the original Komatsu cylinder blocks, or the optimized and widened oil channels. One could argue at this point if the uneven pitch makes that much of a difference, but it does tell you immediately the barrel is not genuine. The second pic shows the swashplates for the same pump model, the casting quality of the aftermarket swashplate is notoriously low, as well as the finish. Will such parts work? Yes, they will, probably, but...
This aftermarket valve plate (on the left side) for the Sauer Danfoss series 90 closed-loop pump is almost perfect! Can you spot what's wrong with it? The round notches, which are supposed to be a tight fit with the end plate guiding pins, are over-cut - so the valve plate can move a lot! It's normal for these valve plates to exhibit some play when in place, just not that much!
This shaft from a Rexroth A8VO pump has only eight (!) hours of operation. The steel is too fragile, most likely due to a defective heat treatment process.
Aftermarket spares only look nice until they are put next to the original ones. The images speak for themselves. The aftermarket A4VG swashplate (on the left) is from a working pump, however, the small imperfections immediately reveal its "oriental" origins. The casting is porous, there are small machining faults, and the part looks unfinished. It does work, though, but I still don't like it! And check out the original and non-original swashplates for A10VO pumps! Note the skewed lubrication channels - they do the job, but the machining quality speaks for itself.
This aftermarket ball guide pin for the Rexroth A10VO pump has an incorrectly shaped head - you can still mount it, but you will have to cut the spring support shim a little (make small grooves in the places where the pins work). The part does its job - but if you don't know this detail, you will struggle to mount these pins into the barrel assembly. Why would anyone bother cutting costs on such a cheap part anyway?
This aftermarket ball guide for the Sauer Danfoss series 20 (on the left) looks absolutely perfect. The catch is - it's too tall, so when you mount this beautifully finished part into a pump - it jams the rotary group! And how about this series 20 cylinder block? Do you see it? The hole for the port plate pin is in the wrong place!
Tons of "white market" pistons for Rexroth A6VM motors on the market. All look nice, but the quality varies a lot, and in the worst-case scenario such pistons can end up looking like this after but a couple of hours of "hard work". Here are three tell signs to determine if an A6VM piston has "oriental roots":
Of course, I couldn't skip the subject of seal kits. Getting a good aftermarket seal kit is a harder task than one might imagine. Even original seal kits may miss o-rings and seals. This is what a cheap aftermarket seal kit looks like. The o-rings are of an acceptable quality, but half of them are of the wrong size and the other half is missing, which makes this seal-kit something one can charge for, but, sadly, can't use.
