Insane Hydraulics

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Getting Those Hydraulic Knowledge Nuggets

I'll start from afar.

The ubiquitous Danfoss PVG32 is one of our best-selling products as a mid-range proportional directional control valve with a modular design and a decent range of options. This is not praise or anything like that - these valves are what they are. And, of course, like any decent representative, we stock most of the PVG32 components to be able to assemble and supply custom solutions on the spot.

I started my career in hydraulics as a shop hand, and so naturally I mounted and tested hundreds of these modular valve banks over the years. That's how things are organized in most shops these days - the engineering (or sales) department comes up with a valve configuration, then a parts list is sent out to the warehouse, where the parts are gathered and sent out to the shop, where the grease monkeys take care of the "dirty" part - i.e. the assembly and the testing + adjustment.

This flow of work is functional, but it has the drawback of separating the theoretical part of the valve-building process from the practical, which, in my opinion, is bad for both "parties".

Office engineers can be superbly good with part numbers and calculations, but if they don't give due attention to the "hands-on", they impose a serious limitation on themselves, which creates a risk of making an occasional and perhaps non-intentional, but nonetheless expensive and/or embarrassing mistake. And the grease monkeys (such as myself) while being good with their hands (hence the "hands-on") can't expect any real progress in this metier if they don't invest in discovering the theory behind the bits and pieces they are fiddling with every day.

The scene I am about to describe is from my shop-hand days.

As usual, I received a box with PVG32 parts, with the customary instructions of "assemble and set to .... bar". So, I picked the box up, peeked inside, and said something like "Wait, dude, it won't work! The parts aren't right...".

Stop everything! The natural order of things has been violated! How dare you say these things, hand! At least that was what I saw written on the face of the person who gave me the box with parts. That and the silent "Shut up and do your job!". But of course, I heard something different, something along the lines of "Don't you worry about the parts, kid. The parts are OK. Now be a nice lad, and put the valve in one piece and test it, will you?"

I wish I could say the discussion ended then and there. It did not, unfortunately, and the "clash of egos" continued, with me saying that at least one of the parts was not right, and the other party saying that the parts were perfectly fine.

Usually, I let such situations play out as a "silent observer", but I had zero spare time that day, and so when I saw that there was an obvious telltale that a key part in the parts kit wasn't right - my mind went: "an hour to assemble the damned thing, another half an hour to hook it up to the test bench, them test it, then it won't work, then watch the engineer walk around the test bench scratching his head, then wait for the right part..." Well, you get the picture. It's fun to look at, but not when you're short on time, and so I needed to skip to the "end of the show" right away.

Let me tell break the suspense and tell you what it was that I saw now. It's very simple, actually, at least for those who mount these valves all the time. The inlet (pump) modules of Danfoss PVG32s do come in many configurations, and you do need a part number and a catalog (or a good memory) to determine which one it is, but there's one thing that is "universal" for all modules - you can always tell if an inlet manifold is prepared for working with electric controls or nor by the presence or absence of the pilot pressure reducing valve.

The valve is situated right next to the relief setting screw in a separate cavity, which is "extremely apparent". If it's not there - this inlet module can't be used with electric controls. Simple. You can't, obviously, read a part number from a distance, but even if you're meters away, you're able to tell if an inlet manifold has this cavity or not.

What I saw that day, was a bunch of PVG32 parts in a box, and the fact that there were PVE actuators there (electro-hydraulic) told me that the valve was supposed to have electric controls, and yet I saw the inlet manifold without the reducing valve cavity - which immediately told me that whatever the configuration was, the pump manifold was incorrect because it would not supply the pilot pressure necessary for the electro-hydraulic actuators to work.

Now let me show you how this very distinct "bit of PVG32 knowledge" helped me out last week. So, I hear the story that a brand new PVG32 (supplied directly by the Danfoss factory, by the way) gets mounted on a piece of equipment and simply does not work. The mechanics are called, the electrical and instrumentation techs are called, a shift of production is lost and nobody can tell why the valve is dead. In the end, an old PVG32 from a similar piece of machinery waiting for an overhaul gets mounted as a temporary fix, and production is resumed.

As soon as I get to the client's and see the PVG32 on the floor - I know, or better - see the reason it didn't work. Have a look at these pics, one of the valves is the brand new dud, and the other one is the old one that works. I bet you can tell where the problem is now:

Once again - no reducing valve = no pilot pressure = no electric function. I am investigating what happened because it's virtually impossible for a valve to come from the Danfoss factory in this state. Maybe someone needed parts and used this one as a donor at some point?

Had the engineer from the first tale had more hands-on practice with this series of modular DCVs he would have seen the mistake by himself - but that's not the point today.

Had the guys who supplied the assembled PVG32 known that a reducing-valve-less inlet module on a PVG32 equipped with PVE actuators is a big no-no, the mistake could've been caught even before it left the warehouse - but, once again, that's not the biggest point here.

The biggest point is - when you work with oil hydraulics in an office position, be it sales or projects/engineering, embracing the (sometimes nasty) hands-on part of this business arms you with unique nuggets of practical knowledge, that have the potential to raise you substantially above your competition. All you need to do is not be afraid to get your hands dirty and, of course, keep your eyes open "for the said nuggets".

Will you be able to troubleshoot stuff without it? Of course, you will. But having bits of practical knowledge under your belt will help you do it faster, sometimes way faster! Like the PVG32 bit I just told you about.