Testing of home-made pneumatic rams

I made the ram myself at work from some hydraulic tube. It was built with theyre help and guidence (the company is Southern hydraulic and the make and repair hydraulic rams). So although it is not strictly a modified hydrualic ram, it is exactly the same thing thay theyd sell if you went to them and asked for a custom ram. The only difference are the seals, which are rated to a lower pressure (about 150Bar iirc) but are of a nice low friction. Under the rules is it acceptable If i hydraulically test it to about 150Bar? (seeing as it *is* a hydraulic ram, made custom at a place which builds hydraulic rams)

P.S Im aware of the dirrences between static and dynamic pressure testing. But this ram is pretty belt and braces :)

Okay, my first post on this forum, but here goes...

There is a huge difference between the energy stored in a compressed gas and a compressed liquid for the same pressure (compressed gas store orders of magnitude more energy than a liquid for a given pressure due to the substantial difference in compressibility and the whole P*dV work stuff). Is there any difference in safety guidance between gas vs. liquid systems? It would seem that gas systems would be more strictly controlled. If a gas system fails, the energy release and associated hazard of this failure would be much higher than for a liquid system.

Regards,
Mack

You are entirely correct, but it is quite difficult to actively discriminate between the two. It is best to take the view that they are both very very dangerous (or rather, have the potential to be if mistreated) and extreme care and caution must be taken which designing and building both systems. If either of the systems to fial, lets hope its in the arena. To give an idea of the magnitude of the mess of a system failure, I would point you towards whichever heat it was whan Spawn Again losts its End cap when running a Low pressure ram on Full Pressure. Certainly not something youd want to happen in your garage, but nothing the arena couldnt cope with.

I have a question based on what weve acheived above in the conversation: should I treat my purpose build ram as a hydraulic one when interpreting the rules? Or should i just be safe and pressure test it to 200Bar?

Eddy .....There is a BIG event on this weekend .....so I doubt that youll get an official type answer much before Tuesday..

You dont need to tell me Alan- I wish I was there! I was just posting so that its there ready for monday :)

Well ... In lieu of an accredited expert Ill throw in my twopenorth.

Id suggest that you get your company to treat it as they would any other hydraulic ram and certificate it to a working pressure of 150 bar ... It would then become a standard ram.

This should result in a ram that ( when its derated by 50%* ) should easily meet the FRA rules.

* If you take an unmodified standard hydraulic ram, you can use it on pneumatics to a pressure level of 50% of the rams hydraulic rating or 1000 psi - which ever is the lower without requiring further test certification

Im working on the assumption that Pauls hydraulic rating is refering to working pressure as opposed to test pressure.

Eddy, assuming the ram has been built using standard cylinder tube, rod and end caps that your employer would normally use then it sounds very much a standard ram to me. I would suggest that you ask your employer for a certificate of conformity for it to confirm this fact. Thank you Alan, that just about sums it up.

Mack, all pneumatic systems are considered as gas systems rather than liquid even though the CO2 is stored as a liquid and sometimes injected into rams as a liquid. This is because the CO2 liquid rapidly boils off as a gas when the pressure drops.

Paul
FRA Technical Team

Thank you paul. I will do that- its not quite built as a normal ram in that I have stronger, tie-roded end caps and low friction o-rings, but certainly it could pass as one :-)

Many thanks for your confirmation,

Eddy

Slightly off topic I know but I was just curious. Do I need a cert for my 600g bottle? I have pressure test certs for my ram, valve, buffer and my 2 prds but I dont have one for my 600g co2 bottle. Do I need one or does everyone just kinda say ah well its a 600g bottle we know thats safe.

Regards
Ian