Insane Hydraulics
Bold and audacious blog about fluid power
I've always liked Parker's PV+ series of pumps for their robustness and ability to withstand abuse. When a client asks for an especially reliable open loop pump - my first recommendation is always the PVplus. We sell and repair all brands of pumps, and after you do this for a while, you see that some models "return" way faster than others, and then you form an opinion on what pump you would choose for your hydraulic system if you had one. Regarding open loop pumps, the PVplus units have no real competition, in my opinion.
There is, however, one small thing that I would like to see changed in their design. Actually, no, not a small thing, but a full-blown design flaw (once again purely in my opinion, based on my experience), and it is the damned M6 grub screw plug in the swashplate (part Nº99 in the exploded view below), which seems to be always falling out from where it is supposed to be "fixed for life".
A swashplate kit is supplied with a "universal swashplate" (i.e. suitable for both LH and RH operation), an M6 plug (99), an M6 orifice (12), and a 1/16NPTF plug (25), which you then mount in the swashplate according to the required direction of rotation following instructions in the included installation manual:
So, this week I opened yet another 15000 hour+ PV180. This one got impaired by unscheduled hydraulic fluid enhancement with especially generous amounts of water from a blown cooler:
And, once again, after I emptied the pump case over my bench - the already customary escapee fell out:
I would consider this a fluke if it was a one-time deal, but it's not. And I have, actually, documented this before:
I praised how well a PV140 pump got preserved after 14000 hours of operation. I wrote an article about an open loop pump longevity hack, using the same unit as an example, and then when I received the parts, I found the loose swash plate plug and wrote an article about escaping grub screw plugs.
Documenting things is useful because in the first article I mention (and even find curious) the distinct mark that piston slippers left on the swashplate sliding surface when they were passing over the orifice that was vented to tank - and you can see that it never occurs to me at that point that this is wrong! The hole in the swashplate surface is not supposed to be open to the pump case - it is supposed to be plugged! You can also see how I only discovered the loose plug in my third article, by accident, when it fell out of the casing and made a clinking sound I happened to hear!
This is the third pump that I have found with the loose plug, and I feel that I need to leave the following direct recommendation for the pump guys:
Whenever you overhaul a PVplus pump, make sure you check if the swashplate plug is where it is supposed to be. And be ready to fish it out when you crack the casing - don't just dump all the case oil out, do it in a way that you can see what is "leaving" the pump! There's, apparently, a good chance of you coming about the loose grub screw!
In my opinion - a tiny grub screw with a dot of Loctite on it is not a safe choice for a swashplate lubrication channel plug, and the Rexroth's A10VO series 52 is another testament to that! I would gladly prefer Parker manufacture distinct RH and LH swashplates for the PVs with a single lubrication channel of the right size, capped off with a proper tapered break-off plug.
I think that tapered break-off plugs are more reliable than grub screws because the taper locks better and takes some of the holding stress away from the threads.
And, by the way, now that we talk about break-off plugs, I want to mention one more thing I learned the hard way just the other day:
When you order a Rexroth pump control body (just the body part, not a complete assembly). it is supplied without the break-off plugs in it! So if you don't have them handy - you are in trouble! I ordered this manifold the other day (the pump control was smashed against the tunnel wall during transportation) and here's what I got:
See all these threaded holes with a taper at the entrance? They are all supposed to be blanked off! Luckily I had some of the plugs in the shop (here's another free tip - if you need to order two of these, order 12 - you never know when you'll be needing them)!
But let me get back to the Parker swashplate now. I also checked the other side of the swashplate, and both the external plug and the orifice were in place and well-fixed:
I am not 100% sure about why this is happening (high-frequency cyclic loading?..), but the multiple "loose grub screw" cases that I caught with Rexroth A10VOs and now the PVs make me consider the use of a grub screw (be it a plug or an orifice) with a thread-locking agent inside a swashplate an unreliable solution. So, Parker engineers, listen up - ditch the glued set screw in the swashplate - it's a weak spot in an otherwise strong (almost perfect) pump!