Insane Hydraulics

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The Ideal Hydraulic Pump Test Bench - Part One

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.

This post is based on these flimsy sheets of paper I stumbled on when I was re-arranging the pile of my "old but for some reason still important" papers last week. These notes are about 15 years old, and I thought they were long gone.

So glad I found them!

Back then I was testing pumps on an old test bench, built by the "previous generation" in times when the likes of Rexroth A2V or Danfoss series 20 were state of the art, so it was basic... very basic. An electric motor with a bell-housing, a set of couplings and flange plates, an oil tank, and a panel with a flow meter and a needle valve coupled to a large hand wheel to induce pressure. An AK-47 of test benches. It was ugly, it was crude, and it never failed. I liked it. I ran countless closed-loop units through it at 450 plus bar, sometimes even 500 bar, and never had any issues.

I was in my twenties, and, like most young techs, I was very enthusiastic about the technical aspects of my job but had zero corporate experience, so I didn't even know the questions like "who's paying and how much does it cost?" existed and lived in my nice and cozy "technical bubble".

As I would run the bench tests, I saw a lot of things that could be improved to make my job easier, and the pump tests (and, consecutively, the overhauls) better, and after a while, I began to take notes. Every time I saw something that could be better or come in handy, I would write it down. The list grew, and after a pretty decent while, I had three A4 pages of what I thought to be "pure awesomeness" lying in my toolbox and waiting for its moment to shine. Ah... So many shades of ink on these...

I thought that one day the question of upgrading the test bench would surely come up, and I, as the one who was using it the most, would be the first person the management would have to talk to, and then I would proudly produce... no, wait, even better - I would proudly throw my so very meticulously gathered notes on the table in a dramatic fashion and say something like "Be amazed, friends, for these are the plans for the Ultimate Test Bench!!!" In my imagination, as I would say the last three words, there would be a sound of distant thunder in the background and the lights in the room would begin to flicker.

What a naive creature I was! Eventually, the question of the bench upgrade did come up, and I, indeed, was invited to participate in the VIP meeting, and I did bring the notes with me... and, nobody even got curious to learn about the oil-stained sheets of paper the shy greenhorn tech was holding in his trembling hands while staring at his feet!

People around me were discusing prices, delivery and payment terms, ready-made systems, and a whole bunch of other crap I didn't care about, but nobody seemed to be interested in talking about the technical aspects of the bench they were planning to build and use! Truth be told - one person got curious. He looked at the papers, then at my anxious face, then sighed and looked away... his face clearly saying "You have so much yet to learn, young grasshopper..."

I thought it was crazy! I could not believe it! And yet there I was - at the end of the meeting, having said nothing. No background thunders for me that day... One of the first corporate lessons I learned the hard way - Nobody cares about ideas for everyone has tons! Execution is king and concrete business plans with positive profit margins are what gets money moving, not the cheap suggestions on how to make things better.

But what about the notes? I got so baffled back then, that I decided to put the whole ideal test-bench idea "on indefinite hold", and up until last week was pretty sure that I binned the papers for good. Yet - here they are, in front of me, oil stains and all. A time capsule message from my younger self. My dearest Nostalgia, how sweet art thou!

It would be a shame to let the notes get lost again, so I decided to put the list up in the blog as a testament to how "simple" the world is around a wide-eyed tech who just discovered hydraulics and thinks that everybody around him should feel about it as strongly as he does.

To the list, then! I will be putting the things down just as I wrote them, and then add comments.

Stuff an Ideal Pump Test Bench Should Have

Oil temperature monitoring system with large displays, one sensor for the test loop, and one for the oil tank. Maybe one external contact probe.

I like knowing the temperature of hydraulic stuff when it's working. Our flow-meter did have a temperature probe in it, but during long tests, I never knew the temperature in the tank, and sometimes it would get pretty hot, so I wouldn't mind monitoring it.

An on/off loop flushing system with a possibility to choose between an adjustable relief valve and a compensated flow control valve for flushing, and a flow meter to monitor the flushing flow.

I would really love to see a test bench with a system that used the setup similar to what I described in my post on testing closed loops in the field. A that point there was no loop-flushing of any kind in our bench, and the closed-loop tests had to be performed lighting-fast to prevent the loop from overheating, so whenever I'd need to perform an exhaustive test or an adjustment - I'd have to wait for the loop to cool down, something I didn't like at all.

A torque meter on the input shaft, and an accompanying software system for real-time rpm/torque/power monitoring and logging.

I could kill for one of these back then! I would love to be able to get an instant readout of the input torque, input RPM, and also (of course!) input power and then to be able to compare it with the hydraulic power the pump is outputting. I would obviously need the "magical software" to be able to take the instant flow and pressure readings and transform them into kilowatts. It would be an ultimate efficiency tester - a way to scientifically prove and register the overall efficiency of a hydraulic unit. Nothing would ever beat that! (By the way - developing such software today, graphical user interface and all, is way easier than it used to be, and is possible with a single developer! Insane, right?)

Two independent pilot pumps, one of which high-pressure capable, with a flow regulator (or variable displacement).

You can never have too many pilot pumps on a hydraulic pump test bench. In my dream world, I always wanted to have at least two. One would be for controlling low-pressure hydraulic pilots, and the other (the high-pressure one with regulated flow) would serve as a charge pressure pump for the closed-loop pumps that use external charge pressure supply, or it could also be used as a high-pressure source for testing stuff like torque summation controls and whatnot.

Main relief valve with an easily accessible adjusting knob and a visual setting feedback.

Ours was placed in a "funny place", and kind of hard to turn, plus I could never tell the setting unless I tried it, and I would really love to see some kind of a visual feedback system that would give an instant idea of the current relief setting. I can actually think of several ways to achieve this, but even a simple solution, like a mechanical dial or something, would be great.

Reversible loading circuit.

The old test bench was a simple flow-meter placed on a panel and hooked to a couple of fast couplings. This simple solution meant that when I was testing closed-loop pumps I would always need to swap the loop hoses to test the other half of the pump. Even with fast couplings, it was never convenient, so a bi-directional testing solution would be welcome.

"Onboard" LS system.

This is another one I had to struggle with all the time. LS pumps are so common, and whenever I'd need to test one, I would always have to hook up an external "restrictor thingamajig" to simulate a resemblance of an LS circuit in order to test the pump control. And then spend more time dismounting the contraption from the test rig. My perfect test bench would have this system built-in, ready to be used when needed.

JIC type connections and fittings.

About that - the old bench had metric pipes and 24º connectors with cut rings, which would occasionally develop leaks. I have always had better experience with JIC flared pipes, plus I trust them more in "explosive" situations (you know my opinion about inevitable oil showers) - so yeah - I would use JIC over the 24º stuff any time.

Electric motor controls on the main panel.

In our case, we had the variable frequency drive placed on the wall next to the electric cabinet, and so one would have to go to it first to start and adjust the speed of the electric motor, and then go back to the flow meter panel. Very inconvenient. A dream test bench must have a centralized control panel with everything in it.

Emergency stop buttons.

Yep - we had none of those. The fact that the motor control was "over there" made emergency stops impossible. In so-called "dangerous" test situations a second person was needed to hold a finger on the "stop" button. I say - place several emergency stop mushroom buttons in strategic places and be done with it!

Pump in a protective shroud (shield, screen, etc...).

I would love to see this, or at least something like this. I am used to working next to operating hydraulic equipment, but I (and probably everybody else) would feel safer if I was behind an acrylic panel or something when a unit goes "pressure up". Just in case...

Nice knobs and buttons.

A proper control panel must be good-looking, period. I am talking about control placement, and control external appearance - it should be both functional and aesthetic.

Built-in electrical control board with several on/off and proportional (PWM) outputs, obviously with current/voltage regulation and monitoring.

It would be used for controlling proportional and on/off valves and it would have to be current limited and short protected, of course. Then I would want a well-placed display to monitor voltages and currents. Preferably on all channels. We would always have to "devise" a way to control this or that pump, and when I'd need to check the current and/or voltage at the same time - there would always be a mess of power supplies, proportional cards, and multi-meters strewn around the "testing site" - very painful to look at.

A cabinet with a set of cables with all sorts of connectors.

Another dream of mine that never came true. I'd get all sorts of connectors on units - DIN, military, Deutsch, Japanese... You name it! There would always be a need to hot-wire something with a pair of stripped wires or, maybe, alligator clips at best. In my dream, I would open a cabinet, take out a prefabricated connector cable, hook it up to the pump, and be set!

Two tank line flow meters, one for big flows and the other for small.

A great thing to have for monitoring and logging case flows and whatnot. You can never have too many flow meters in a test bench, you know.

Electric motor current and RPM display.

A nice feature to have in a test bench, especially if you want to teach folks about the power factor. Truth be told - a remote VFD control panel usually displays these values, so I probably didn't need to write this point down, but I did anyway.

Conveniently placed AC sockets.

Sometimes I'd need to use a power tool when working on a pump, and I would always have to fetch an extension cord. A couple of AC sockets is never a bad thing to have on hand.

A pump case filling system. Internal and external.

Often one can fill a pump case by simply turning on a pilot pump that lightly pressurizes the gallery the case is connected to, and then cracking a case plug or something, but sometimes you can't do that and have to physically fill the pump case with oil before you start it. Funnels and jugs filled with oil are troublesome, and the worst thing that could happen would be me spending the whole day assembling a pump with a thousand and one o-rings in it and taking all the cares in the world to make sure that it starts the test in the "overall dry " condition, so that I could be sure that nothing is leaking, and then spill a cup of oil all over the control module as I was filling the case. A valid reason for a shop rage episode, if you ask me. So yes - I would envision a small hose with a dispenser gun to be able to fill units with less hustle.

Drive motor capable of reaching 2500 rpm.

This is quite important for some cases, like pumps with automotive controls, that do need to reach these speeds for proper testing.

"Oil spill ready" benchtop and floor in the test area.

I guess that's a given. When you work with hydraulic pumps you have oil spills. I would always, and I mean always, have to clean and mop the floor after tests. So, an ideal testing bench has its "pump space" prepared for major spills.

System to recover spilled oil.

I actually already wrote before about the recovery of hydraulic oil spills. In short - I believe that discarding spilled oil is a waste, but I also believe that one can only re-use it after it's properly cleaned. A nice bench should have this thought through and allow for an easy spilled oil recovery and reuse.

Decent filter bank.

A decent test bench will have a decent filter bank. Not a single pressure filter, like we had back then. I would also love to see a bench equipped with an oil particle monitoring systems. These systems are much cheaper today than they used to be, so it's not an overkill these days. Ideally, one would be able to monitor the particle content both in the test loop and in the tank. I guess I really enjoy monitoring stuff...

Well - that does it for page one. I have two more to go, but this post is already too long as it is, so I will be putting the rest of the items from my "ideal hydraulic pump test bench" list in part two.