Insane Hydraulics
Bold and audacious blog about fluid power
I've always liked the quality of Sun Hydraulics cartridge valves, and in my practice, it has been the brand with the highest quality/price ratio, hands down. I've also always secretly hoped that this would never change, but, whether we like it or not, things change... and, unfortunately, not always for the better.
I got my first SUN-related heads-up when I came across the peened orifice design, which was not great because the orifice would occasionally "unpeen" and get lost. Today I want to show my latest "SUN surprise" - the upgraded retaining ring, which, honestly, blew me away.
This story had its origin when a friend of mine pulled a SUN valve from a manifold on his rig and discovered that the nose of the cartridge decided to stay behind. It's always fun when something like that happens in a mining environment over a terrain that can be described as “drop it - lose it", and you suddenly find yourself holding a bunch of internals from an apparently sophisticated cartridge valve, uncertain about their order or even if you have all of the parts at all! But wait, there's more! A couple of weeks later, it happened to another valve of the same model. Not the best of patterns to witness, is it? And so, the man brought a couple of these valves to our shop for a "professional investigation."
These are the DODS-XHN - normally open, balanced poppet, pilot-to-close logic elements for the four-port T-21A cavity. One of the valves had its nose "removed" by the predicament, and so we decided to disassemble the other one. I am actually cheating a little bit here - the image above shows the valves after we took them apart, I just fit the parts back on one of them to show you how the valve is supposed to look when it is still in one piece. Why am I saying this? Because if you look at this picture after reading this article, you will be able to tell immediately that this is the case.
Anyhow, how do you disassemble a classic cartridge valve from SUN? I already showed how in my post on the peened orifice - you look for the slot through which the retaining wire is inserted, rotate the nose till you find its end, and then pull it out through the slot while rotating the nose - a bit finicky, but definitely doable. So, we tried to do the same to the assembled cartridge - but when we looked inside the customary slot - instead of the usual dark colored steel wire, we saw something red (this is how you can tell that the picture above is "fake" - you don't see anything red in the slot).
So, we tried pulling the red thing out through the slot - but poking it with a sharp tool revealed that it was made of plastic, and no matter how we tried, we could not coax it out. Now, my friend is not very patient, like at all, and after several attempts to carefully wiggle the plastic thingy out of the slot "scientifically", he said something along the lines of "#"*#, I don't have time for this!", and gave the nose a hefty tap with a screw-driver end and - boom! It popped right off!
As it turns out, instead of the classic steel wire circlip, these cartridges had a retaining ring made of plastic. No way! - said I. But then I decided to see if I could find more SUN valves with the plastic retainer rings - and the more I looked, the more scared I got. All of these logic elements I got last week (normally closed and normally open) came with plastic instead of steel - you can clearly see the red in the slot:
Then I wen to my SUN scrap box - and looked though the cartridges I had there, and I had my second "No freaking way!" moment - even my beloved PBDBs (if you work with drilling equipment, I am sure that his reference rings the bell), apparently, had been upgraded at some point, because I found a cartridge with the classic wire and a cartridge with the red plastic retaining ring:
Damn! I decided to see if the internal parts were any different - in other words, if the "upgraded" valves could still be saved. The steel wire one, as always, was pretty easy to disassemble:
And as for the one with the plastic ring - I managed to easily pry the nose off with a screw driver, but the ring, obviously, got destroyed:
Here are the valves side-by-side, and as you can see, the "upgraded" design has a differently shaped groove and no hole for the end of the wire clip, which means that, sadly, these valves "can not be saved."
Here's why I don't like this design:
The plastic ring is definitely weaker than the wire clip - apparently to the point that the cartridge can disassemble itself when you screw it out. I imagine that when a system is hot, the plastic becomes even softer.
The plastic retaining ring gets destroyed on disassembly, and this means that cartridges with this design can't be disassembled in the field. Now, I do realize that disassembly of what, essentially, is a non-serviceable part is an advanced move, but sometimes such valves malfunction merely due to a clogged orifice or a damaged internal seal, and being able to disassemble them can be a lifesaver in situations when you don't have a spare on hand.
Honestly, I see nothing wrong with the classic steel wire design, and I don't see any reason to use the plastic stopper other than to make production (slightly) cheaper.
I thought I would never be directing the following phrase to Sun Hydraulics, but there's no way around it, so here it is: "You used to be cool, but you changed, SUN! The steel wire was so much better than the plastic!"
P.S.
If you know a way to disassemble these cartridges without destroying the plastic ring, please let me know!