Certification of Full Pressure Ram

[maddox10]

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?

[JeremyCuss]

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.

[maddox10]

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.

[emisnug]

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.

[JeremyCuss]

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.

[JeremyCuss]

Today the ram with the new seal has been tested and certified at 90barg. Hurrah! There was a small leak of water past the O ring, but nothing of any consequence. I have now got a ram which meets FRA and Robot Wars rules for custom-built components when used with full-pressure CO2. I ended up going to a local firm, Hebble Hydraulics, for the pressure test on the ram. This was a lot easier than going back to the West Midlands. The cost of £40 was the same as I was charged by HPAC.

[maddox10]

Good to hear. After 13 years of idleness that ram finaly can fullfill its destiny.