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Today I continue the "investigation" of the A10VO100 pump that dumps about 20 liters per minute into the casing even after the complete replacement of the rotary group - Leakage of Rexroth A10VO DFR Controller.
I wanted to find out how much the bias servo-cylinder, which is always connected to the pump outlet, adds to the case drain flow in a Rexroth A10VO100 hydraulic pump. I was also wondering if the noticeable wear mark on the sealing surface of the piston shoe would add much to the leakage. Surprisingly, the leakage is extremely small. Even for the heavily marked shoe. Details (and a video) can be found here - Evaluating Leakage of a Rexroth A10VO100 Bias Servo-Cylinder
I created this blog because I like hydraulics and because I believe that sharing knowledge is important. But after having run it for a while, I feel that it is almost like a journal for me. Looking through my older posts brings back memories and makes me realize how fast time flies. Today I am republishing a blog post that I wrote when I got back from my trip to Africa in 2011. I'm so glad I wrote it fresh off the plane - because it captured the state of the mind of a young tech returning from such an interesting adventure. I am sure that some things are different there now, and some are probably still the same. In any case - I enjoyed getting back to it, and I invite you to have a glimpse of what fixing hydraulic equipment in Africa was like eleven years ago - Hydraulic Battles in Guinea Bissau.
Another timeless battlefield story today, with five valuable lessons at the end - Inventing A New Load Sensing Valve.
I have to admit that I got carried away with this one. I sat down to write a simple one-page post about the viscosity of hydraulic oil, then one thing lead to another and... well, let's say that if you do get to the end of it, you'll never have to ask how kinematic viscosity is different from absolute, and why air is more viscous than water, and what all these centistokes really mean. It's a lot of typing for a single evening, so you may find some errors or typos - I'll try to clear them out during the week. So, without further ado - I present to you - Absolute vs Kinematic Viscosity of Hydralic Oil.
About the o-ring leakage from last week. I tried cold contacting SUN folks, and I made a post on LinkedIn describing the failure and the test I ran to recreate it, and asking if anyone could explain the mechanics behind "o-rings working as pumps", but unfortunately I have zero news so far. I'll keep waiting... And today's post is about the time when a hydraulic tech wants to shoot the piece of machinery in front of him. Literally. An old troubleshooting story about an Inexplicable Malfunction of a 1210B Forwarder Hydrostatic Transmission.
Results of my attempts to recreate Interface Leakage Caused By O-rings Working as Pumps.
Two older articles get a "facelift" today (and the https): Evaluating Drain Flow With The Five Plus Five Rule and Quick Couplings in Hydraulic Motor Drain Lines. (Don't forget to press reload if you read them before).
A couple of days ago I was asked to troubleshoot a Danfoss PVG32 DCV that "wouldn't work for some reason", and boy did that bring back a lot of memories! "Dude, it won't work!" - is the key phrase of today's post about Getting Those Hydraulic Knowledge Nuggets.
The library is expanded with the Interactive Standard O-ring Size Table. I'll explain the motivation and talk on the subject of o-rings next week - putting all the data dogether took more than I expected...
An interesting pump control solution in Rexroth A7VO55LR3E Open Loop Pump
I've been working non-stop doing the annual maintenance at our mine for the last two weeks. Luckily the production is to start tomorrow, so I should be "officially free" pretty soon. I am writing this post as I am waiting for the green light for re-commissioning the stuff that I serviced, and I apologize if my latest posts sound like a rant of a person dead on his feet... I also wanted to share some pics from this stretch, so here it is: More On Pressure Filters and Hose Replacement.
Danfoss PVEH Electrohydraulic Actuator - What's Inside? (Includes a free tip on how you can fix a "broken" actuator).
If you want to see what a blocked NFC pilot orifice looks like, check out today's post about A Common Malfunction of Negative Flow Control Systems
Some "Kaboom" edits today:
Modern electronic control systems can be easily messed up by things that would never affect good old relay-based circuits - False Triggering of a PLC Input
This post contains service practices that can be regarded as "borderline safe" or even "downright unacceptable" (like removing a relief valve from a hydraulic system or checking a flow rate via "visual hose-end inspection"), but I like telling stories as they happened, and hope that people can learn something from them, even when my choices weren't the "safest"... Troubleshooting Slow Transport Belts on a Tomato Harvester
An old story that proves that hydraulic troubleshooting is all about people - Straightening Out a Crooked Split Barge
A mere reminder that hydraulic machines can have more than one oil tank.
Following last week's trend, I keep answering questions of the type "What would happen to my "...insert expensive hydraulic component..." if I "...insert an inappropriate action..."?
Finishing the pump horsepower control series with two more ways to achieve a perfect (hyperbolic) pressure/flow curve - Tackling Torque Limiting Pump Controls - Part Five.
Going "hypebolic" today in Tackling Torque Limiting Pump Controls - Part Four.
Finally - the troque limiter control adjusting screws work as they should (plus a power shift function) in Tackling Torque Limiting Pump Controls - Part Three.
I continue with the topic of double-spring feedback torque limiter controls of hydraulic pumps, and present to you an updated graph and some animated springs in Tackling Torque Limiting Pump Controls - Part Two.
I invite you to build a simple torque limiter pump control with me in Tackling Torque Limiting Pump Controls - Part One. There's an interactive chart inside, and if you play with it long enough, you will be able to tell why a torque chart of many pumps with these controls has "two humps"...
The year started at full speed, so we've been quite busy, but I managed to find a couple of free hours to give the last week's project a better description. (You may need to refresh the page to view the changes).
My Fiends, the Pressure Maker 2 is finally here!
Hard to believe it's 2022 already! We all had a rough year, yet all that's hydraulic is still "pumping" around here, with no slowing down in sight. I wish you all a great year! And start this one with a reminder that set screw plugs and orifices, often used in hydraulic pumps and motors, are never guaranteed to "stay put" even when glued in place, so it's important to know where they should be and check if they are still there.
I wrapped up all of the emergencies on the 24th, and managed to take the 25th as a day off, which felt great! Hopefully, I will be finishing this year as a sane person. Anyhow, since I've been doing nothing but dealing with scrapped pumps this last week, I'm re-uploading the report from the "bust'a'pump competition" in a better resolution. Make sure your pumps never end up like this!
A question to owners of hydraulic equipment - Should You Cheap Out on Your Hydraulic Oil?
I am working through this weekend, investigating a series of nasty break-downs, most likely related to the hydraulic oil. Hopefully, there will be another "industrial lesson" to share soon. For now - another "oil-related" story from the past - Hydraulic System Failure, Caused by a Chemical Reaction.
The second generation of the "pressure maker" will have to wait for another couple of weeks - I have it built and tested, but the bluing of steel parts and other final touches take more time than I expected. It actually turns out a pretty cool-looking table-top fidget, so I'll show it off as soon as I can.
Today I want to go into pump repairs and talk about a wear pattern that can "fool you" if you're not careful when you are inspecting pump parts, and also tell you a story of how I "got caught" by it and had to rebuild the same unit twice.
The Smart Industrial Monitor venture started about two years ago - and even though I couldn't be happier with the results, I found that very few people shared my enthusiasm, which is why I eventually put it "on hold". At least the development part. I've been using my gadgets non-stop. The pandemic did add a lot to that, of course.
But the webinar gave me a lot to think about, and as I was returning to the project that's been on ice for such a long time, I started to think that maybe reviving the development isn't such a bad idea after all.
As I was looking through the project's history - I discovered (to my surprise and horror) that several related pages were still in the older format, which made it impossible to view them correctly in some browsers. So, I had to do some "emergency re-factoring" today.
The article in which I was comparing pressure transmitters was actually a big deal, so I am very glad it's all fixed now. On a related note - I'm reforming the "pressure maker" from that post. I gathered enough industrial scrap to build a far more elegant and portable solution, so stay tuned - I'll be showcasing the second generation next week!
Ok, so the AFPS webinar has happened, and given the fact that it was my first time both participating and presenting - it didn't go too bad (I think) although my presenting skills definitely "require refinement". It was very scary! But I honestly enjoyed every moment! The presentation pdf can be downloaded here, and the recording of the event can be reviewed here. (Do bear in mind how scared I was...) And also today - a few words (and a tale) about the Reuse of Hydraulic Oil in a Shop.
I have an exciting announcement to make! I was invited by the Australian Fluid Power Society as a speaker to their quarterly webinar to talk about my wireless gadgets. I am super excited! It's happening next week, November 17, at noon (Perth time). So, if you want to:
Please register here. Participation is free and the registration is super fast. I'll see you on the other side!
Today I am comparing medium and heavy-duty pumps, toying with math, and Wondering if This Can Be Considered a Pump "Longevity Hack"?
Service case study of a "longevity monster" - Parker PV140 Hydraulic Pump After 14,000 Hours of Operation in Harsh Conditions.
This case was simple to diagnose, but it describes a very common aeration cause - above oil level line termination - Abnormal Noise Caused by the Aeration of Hydraulic Oil.
Today's case is another example of how bench tests can fail to simulate real-life conditions - Overheating Caused by a Hydrostatic Steering Unit
If you examine the way designers "tweak" the geometry of the axial piston swash-plate mechanism to meet the "swashplate tilting challenge", the boring topic of Pressure-Dependent Swashplate Torque in Inline Axial Piston Pumps actually becomes quite interesting, IMHO.
This troubleshooting episode taught me how to properly read servo-pressures of a closed-loop pump - Reading Servo Pressures in Closed Loop Pumps and Pushing Airplanes
The story (including my theories) of An Impossible Shaft Seal Leak.
Checking Hydraulic Accumulator Pre-Charge Without a Charging Kit - an old, but still valid video included.
The pre-loading of a cylinder block is actually not a mandatory condition for the high volumetric efficiency of an axial piston hydraulic unit. This troubleshooting case demonstrates this pretty well (along with some "creative" testing) - Cylinder Block Lift in a Fixed Displacement Hydraulic Motor
Knowing a thing or two about what is at "the other end of the pump shaft" can't hurt a hydraulic tech. A real life example of this in - "You forgot about the Power factor!"
After talking so much about post-compensation and whatnot, it's only logical that in today's post I am addressing the flow sharing in its "pre-compensated flavor" - Pre-Compensated Flow Control With Flow Sharing?!!
Doing my best explaining flow sharing in Post-Compensation for Dummies - Part Two
Did you know that there are various types of Multi-Function Valves for Danfoss Series 90 Closed Loop Pumps?
The featured video is ten years old, yet the idea is perfectly valid - Sometimes Not Enough Power in a Hydraulic System is... Simply Not Enough Power.
Just a few thoughts about how can one develop an Excessive Case Pressure in Pumps With Internal Drain-to-Suction Line Connection.
Continuing the "perfect pump test bench saga" with Part Two.
Today I am taking another stroll down memory lane to the early days of my industrial hydraulics venture, when I would do nothing but overhaul hydraulic pumps and motors and dream about the perfect test bench.
Can you imagine a hydrostatic transmission malfunction that would cause the wheels of the same axis to turn in opposite directions (burning rubber and all)? It's a lot simpler than it sounds. A story from the "pre-COVID era" - Hydrostatic Drive, Sudden Stops, and Wheels Turning The Other Way Around.
I was not sure where to put this article, and in the end, decided to place it in the section containing tips. It's an experiment I did, but it seems like a workshop tip as well. Lots and lots of pictures in Electrolytic rust removal - I am sold!
The add-on to the last week's article - My Very Disappointing Experience With A Series of Reverse Flow Capable Pressure Filters.
My take on the Use of Pressure Filters in Closed-Loop Transmissions
I love tools. The best present I could ever get is a tool. New or used, it doesn't matter, as long as it serves a purpose and makes my life easier I am happy. And so, in today's post I talk about a handy tool that I have been using for a long time - a (relatively) low-cost oval gear flow meter, which I believe to be The Perfect Instrument for Measurement of Low and Extremely Low Flow Rates.