Hi Jeremy, did your ram get certified in the end? Trev mentioned Robot Wars parts but I didn't catch him before he went off again
No, the ram didn't get certified. The valves were pressure tested successfully up to 90 bar, but the ram leaked very badly around the seal. I am planning to replace the seal, but I haven't done so yet, because of a series of problems, which I am overcoming one at a time. I will then bring it back to HPAC for testing.
That's a shame. O ring sealing is never fun, and rarely right on the first or second try.
What pressure are you trying to seal? I'm alright with reciprocating O Ring glands
I'm trying to seal full CO2 pressure - maybe 60barg. I'm interested in the reciprocating O ring glands that you mention. They sound like the sort of O rings used in my old 16 barg Norgren pneumatic cylinder. They were made with very soft elastomer and appeared to have a lip to seal the pressure. This old cylinder had two seals, but I only need one, as the pressure is at one side of the ram only. I have no idea where to get such seals, nor what the best material of construction would be. Any help would be appreciated.
That ram was made back in 2004.... I can imagine the oring on the piston not being all that happy with 13 years of idleness.
Does the rod/piston move smoothly?
Quite so, Mario. There is no criticism from me of your work. I need to replace the O ring because it is old and does not allow the ram to be pressurised. I may look at other designs of O ring, which may make a better seal.
The ram doesn't move smoothly. The problem is not the O ring seal, but the piston catching on the plastic (nylon?) seal which is inserted in the top plate of the ram. I have sanded and smoothed the ram and the plastic seal to improve the movement and will do some more to allow the ram to move freely.
The only reasons I can imagine why the nylon bushing would case "tightness" are the 2% moisture retainment and swelling it can cause or disalignment.
In the worst case, send it back, and I'll rebuild it.
But I cannot certify it anymore. That capacity went when I changed jobs earlier this year.
Jeremy, it sounds like you have yourself an excellent solution.
However, if you're still interested, this here is the O Ring Bible: https://www.parker.com/literature/OR...g_Handbook.pdf
Ingest all of that and you'll have an ok understanding of all the seals involved. Personally, I tend to run a bit more stretch on the O rings I use (a more shallow groove), but that's because I come from paintball pneumatics, where you're on the edge of a good seal and really low friction. For 60+ bar use, stick to the handbook and you shouldn't go too wrong.
I have now got a new O ring for the ram which is 5.3mm instead of 5mm diameter. The O ring fits the piston beautifully and the ram fits into the cylinder OK. It is of course much more rubbery than the old O ring. We will see how it seals. The advice the I received from the hydraulics supplier was that an O ring will probably seal better that a U ring as the ring slot in the piston was not designed for that type of seal. I will take their word for it.
I have also sanded enough from the nylon bushing to allow the ram to travel freely. I am making progress.
Bookmarks