My strong feelings about keeping operation and service history of hydraulic equipment are well known. I love it when a client brings in a faulty pump, and instead of saying the usual “it was working just fine up until the moment it wasn’t..” and answering all of my questions with “I-dunnos” or shrugs, is actually able to communicate usable information about the working conditions of his equipment, and thus help me form an educated opinion about how a particular unit “handles the real world”.
Unfortunately, such cases are very rare, so whenever I come across one - I do my best to document it, because I believe component recommendations should be backed by proven experience, and despite what manufacturers say - similarly ranged and marketed units will have different life spans when facing the same “not ideal” conditions, so the knowledge of which models are “tougher” (for lack of a better term) is an invaluable asset.
So, today I want to share with you such a service case, involving a pump that I consider to be one of the best open loop series money can buy - the Parker PV Plus. No affiliations here. Quite the contrary, because in this part of the world, the support of this brand... how do I put it in a “less politically incorrect fashion”?.. I think I’ll use the phrase “has room for improvement”. Yes, lots of it... But the pumps are great nonetheless. We’ve sold quite a lot of these over the years, and as of now I’ve only seen a single “suspicious catastrophic failure”. Didn’t get a chance to investigate since the pump’s internals got mushed to pieces, so the normal “hydraulic forensics” was impossible, but all secondary signs pointed to the poor suction line design, so I am granting that unit the benefit of the doubt (postmortem).
Most of the pumps we sold were used in mining equipment - namely - custom built HPUs for core-drilling and raise-boring rigs, subject to the worst working conditions in the world, and thus the best testing platforms for filtering out less reliable units.
We tried them all. Rexroths, Eatons, Danfosses... They all worked, and they all would break after a certain while, usually after a couple of “water-in-oil hits” when a heat exchanger would blow up, up until the day the client gave the PV Plus series a try, and then - the breakdowns silently went away.
Yep - sounds like magic, but that was our experience. Same rigs, same crews, same problems with contaminated oil, and the same “imperfect” working conditions, with the most common failure being a blown cooler, that would contaminate the hydraulic oil with dirty water - a very bad thing for a hydraulic pump. And let's not forget that such failures are never detected right away, which makes things worse. Finally, I have one of these "long-playing" units on my work-bench, and I can “dig into” it:
This is the Parker PV140, that for six years powered an underground core drilling rig and clocked 14,000 hours. The system pressure was set at about 280-290 bar, the hydraulic fluid was a common mineral HLP oil, grade 68. The rig was equipped with a decent water cooling system, which managed to keep the oil temperature at the very respectable 50 C (putting the working viscosity in the range of about 25-30 centistokes, which is ideal), and which also blew out on a number of occasions, filling the hydraulic system with water (and more).
To resume: pressure-vise and viscosity-vise the system was excellent, but the rig suffered severe water abuse on multiple occasions, which for the previous “contenders” would always mandate an overhaul or pump replacement after a short while.
Well, this little puppy outlived them all, and came in labeled as “operational, with no signs of performance deterioration, but probably requiring an overhaul since it’s been such a long time”.
To be honest, I wasn’t expecting a miracle - there’s no such thing. I was genuinely surprised it survived the repetitive mistreatment, but I wasn’t expecting to find the parts (especially the rotary group) intact. Too much water passed through it for that.
So, let us take it apart, and while we’re at it - study the design and see if we can figure out what exactly gives this series its legendary longevity.
The first thing to disassemble and inspect - the control valve:
Nothing beats the hardened steel sleeve/spool combination. (I am looking in your direction, A10VO, with your die-cast control valve body...). This is definitely built to last. Minor wear here, nothing special to look at. This is a single-spool control, and I, personally, like two-spool LS control valves better, but hey - this one works as well.
Let’s see if we can find more interesting stuff. This is the insides of the ripple chamber - the famous PV Plus “invention” that makes this series sound better. I must tell you it really works. These pumps tend to have softer noise, at least to my ears. The oil inside the chamber is actually pretty dirty, and so is the oil in the pump case:
The darker residue in the case oil tells me that small particle contamination may be an issue for that hydraulic system. But then again, anything that works underground is subject to small particle contamination, so that’s no news. Let us continue with our inspection and check out the massive end plate:
The servo piston is very large, and is composed of a hardened piston and sleeve. No seals or rings here - tight tolerances only. The wear is minimal, which is exemplary! The lesson is - make your servo pistons and sleeves out of hardened steel, ditch any seals and/or rings, and design them to be larger and wider - and they will last forever.
Not let’s get to the rotating stuff. The shaft + barrel splines look OK. Parker did a good job of choosing the steel type and the heat treatment. Now, the “pumping stuff” is definitely worn out - the valve plate + barrel surfaces are full of scratches, and so are the pistons and the barrel sleeves:
The piston slippers are pretty scored, so large particles went through there as well, plus they already have play and the top side of the slippers is warn out pretty badly. Cavitation? You will find it only if you know where to look for it. The erosion spots are located on the forward side (in relation to the direction of rotation) of the barrel ports. I wonder if it is not the jet from the discharging ripple chamber that’s causing this pattern. Be it as it may - this unit gets a new rotary group.
The segment based slipper retaining system seems to fare better than the “classic” retaining ball type. The quality of the materials that they use definitely helps. The plate is symmetrical so I could turn it around and re-use it, but I won’t. New parts only.
Now, the swash-plate looks great! I mean, for 14,000 hour of operation! I understand that this is like telling someone that he or she looks great... for their age, but still. The two holes on the sliding surface are for swash-plate bearing lubrication. Only one of them is actively lubricating, because the side plug on the suction side is removed. It is interesting to note that there are two circular wear spots on the slipping surface. The first one appears when the pressurized slipper cavity connects to the first lubrication orifice, which supplies the oil for the pressure side of the swash-plate, and the second one - when the same slipper chamber connects to the hole that is open to the pump case. Like a two-stage pressure reducing cycle, and each time a slipper “feels” the cavity pressure drop - it “punches” the sliding surface and leaves a mark. Curious.
Check out these swash-plate bearing liners. How about that! I am not sure what combination of teflon/bronze material they used for it, but I believe that all other pump manufacturers in the world should copy this system immediately. It is bullet proof!
What else? The shaft bearings are large - just the way I like them. I am not a huge fan of using the shaft as a tail bearing race, but I see why someone would go for this solution - these shafts should be able to transmit lots of torque through them if they need to. This one doesn’t look too bad if you consider the 14,000 hours of operation and the occasional “lubrication crimes”.
The chain link also held up pretty well. If I was to point out the weakest link of this pump (pun intended) that would be it. I didn’t see any play or oval holes. Even in the swash-plate. Also - the steel valve plate didn’t leave any significant marks on the end plate. The steel they used must be really tough. Oh, yes, almost forgot - the incorporated air-bleed valve is a nice touch!