Insane Hydraulics
Bold and audacious blog about fluid power
Today I want to present another DIY accessory that can be of much use to any hydraulic technician. First - I will show you how to make it, then I'll mention some of its obvious use cases, and in the end, I will demonstrate how it can be used (in a rather unexpected way) to test and adjust cartridge-type relief valves without bodies. So, without further ado, let us get making!
You'll need a hefty chunk of a cylinder rod to make this thing. The most common rod steel - the CK45 - is the best steel for DIY projects, if you ask me, and luckily, hydraulic shop workers are blessed with an access to unlimited supply of this stuff in the form of scrapped cylinder rods and production leftovers. In my case, it is going to be this 60-mm-wide slice of a 75-mm rod:
Then you make a blind hole in the center of the "rod pancake" about half of its width deep, and tap the hole with an interface thread of your choice (in my case, it is a 10.5-mm hole tapped with 1/4'' BSPP thread):
Then, you make four more faces on the sides of the "pancake" and, just as before, drill and tap through the center of each of the faces. A four-jaw independent chuck is perfect for that:
And for the optional protective/decorative coating - you degrease the part with a brake cleaner, put it on a hot plate, and watch the magic happen:
Finally - you dip your "freshly baked" part in oil, let it cool, and - voilá - your brand-new test piece is ready - a steel manifold with a solid base and five inter-connecting galleries. Not three, not four - but five!
This is a very handy accessory because it is, essentially, a T-fitting "on steroids" not bound to a specific connector type or size, and the ways you could use such a fitting in your "testing endeavors" are only limited by your imagination.
The point is - some hydraulic tests require joining (and monitoring) multiple lines in a single node, and such an accessory
a) removes the fuss of "chaining Ts" by providing 5 inter-connected ports to work with, and
b) gives you the liberty of arbitrarily choosing the type and size of connecting fittings.
OK, so this part was easy - we just made ourselves a "Super-T" - now what? And now, my friends, I will show you another way to make use of the fact that this accessory has a wide solid base and a threaded port on the top face.
Here's a problem for you - these A6VE55HZ3/63W-VZL22100B motors are already disassembled. They carry four cartridge-type relief valves in total. The nameplates are destroyed by corrosion, there's no official information about the machine or the tracks, and I don't have a body with the right cavity to test them - so how do I find out the pressure setting of these valves to order the new ones? (Rexroth actually said that they need to know the setting of the valves to supply them). Obviously, I can come up with a number from my experience with similar equipment, but what would you do if you really needed to test these cartridge valves?
I imagine some of you are thinking: "Dude, you just showed off your lathe and your machining skills. Can't you make a manifold with the required cavity from another piece of rod or something?" Of course, I can, but I don't want to - for there's a lazier way!
If you want to determine the cracking pressure of a relief valve, you don't need the complete cavity - all you really need is to somehow connect to the pressure side of the cartridge - which, in most cases, would be its "nose" (the hack that I am about to describe applies only to such valves) - and then - if you use a lever-operated pump as your pressure source, you can get away with the open port test relatively safely.
The only special adapter that you will require is a fitting with a hole the diameter of the "nose" of the cartridge valve and a male end that can be screwed into the "Super-T" we just made. These relief vales happen to have 22-mm noses, which means that I can conveniently use a normal 1/4'' x 1/2'' BSP male x female reducing fitting for my "hack" - all I need to do is drill (or lathe) the 1/2'' hole to the diameter of 22 + 0.1 mm and round the edge, like so:
I think we can all agree that making a hole in a fitting is much easier than machining a body with a complete cavity and interface ports. And now you can insert your cartridge into the adapter and then screw it into the top port of the Super-T, like so (looks like a rocket about to lift off, doesn't it?):
Now, the last thing we need to do is find a way of keeping our "rocket" from lifting off when we pressurize it - and you can easily achieve this with a hex socket key for the stopper cap and a shop press for the "removable hard ceiling," like so:
You can see that my 12cc hand pump is bolted on top of the portable workbench (the very same bench that doubles as the base for my powered vertical chuck that I use for manual match-lapping) - it really needs to be that way because of how big the muscular input is for pressures of 300 bar and above. If you want to use a lever-operated pump for adjusting or testing hydraulic valves - the 12 cc would be the minimum displacement I'd recommend (one of the reasons most high-pressure porta-power pumps are not very good for that). The large displacement requires serious muscle input, but it also provides a much better feel for when valves open. It is one of those things that can't described in words - you really need to try it out for yourself to see what I am talking about.
As for the cartridge valves that I tested - they were all set to crack at 300 bar, and I must say that the test procedure was extremely easy and fast. Swapping the cartridges was also super convenient - a small pump with the lever - and the cartridge magically jumps out of the testing socket into your hand. Then you open the by-pass, insert the next cartridge, put the socket key on top, lower the press down - and boom - you're ready to test the next one.
Here's an interesting fact. As I said - when I had ordered the new relieves from Rexroth (R930071620 - pilot-operated poppet-type pressure relief and anti-cavitation valve), I was asked to indicate the setting pressure, so I gave them a number of 310 bar off the top of my head. When I tested the new cartridges in this "lazy rig" - I saw that they were cracking at 290 - 295 bar - which is 20 bar below from what I asked, and I did mention that 310 bar would be the delta-P of the relief setting in case they considered it a closed-loop application. Even if they set it with some 50 l/min the pressure override for the VMR2-22-FC is not supposed to be that big. I am not sure what is going on here - but this is not a problem at all - I'll break the anti-tamper caps and re-set them.
So - there you have it. Another DIY shop piece with multiple uses:
I must say that I love how the blue finish turned out!
A couple of notes about the open port testing procedure. Make sure that you bleed the air from the connecting hose before inserting the cartridge valve - the compressed air pocket can cause the oil to spray out of the cartridge T port when it opens. I actually did try this - and it was much less violent than I expected - but still - do yourself a favor and remove the air from the hose before pressurizing it.
I understand that open port tests of hydraulic components constitute a potentially unsafe practice, but the use of a lever-operated pump makes it acceptable and, in certain cases, even more convenient, in my opinion. I gave it a try, and I liked it enough to let it be a part of my tool set.
P.S.
"...Sergiy, we don't have a lathe in our shop. What do we do?.." Well... I am a firm upholder of the opinion that hydraulic shops must have basic machining equipment and hydraulic technicians must have basic machining skills. If your shop does not have it - it is either a fresh start-up or not a good shop, and I am very, very sorry, if in your case it is the latter.