Testing of home-made pneumatic rams

I have a question. Rule 8.7.1 states Custom made components, or any parts operating above the suppliers max working pressure, must be independently tested and certified at 120% of the maximum system pressure available at that point.. I have a custom made ram which is only 1-way acting, and has holes drilled around the top so that when the ram is at full height the CO2 can escape (gives it a bit more speed when activating). Do I need to get this tested, and if I do, how can I do this if the ram will not hold pressure when activated due to the holes?

Any suggestions greatfully received...

Dave

I assume the CO2 exhausts through these vent holes when the piston has reached close to full stroke otherwise you will be losing power whilst stroking. Assuming this is the case and I am at a bit of a loss to appreciate why you have this set-up, anyway, blank off the holes or limit the travel of the piston to just below the holes using tie rods or similar.

It is not uncommon to have holes around the top of the cylinder to allow the top side of the piston to breath more easily but not the underside (that is usually achieved using a 3 port valve). The way you describe will waste valuable gas and reduce the final velocity and force of the piston.

Or am I missing something?

Paul
FRA Pneumatics advisor

One thing you might try... and Menthorn would look at... If the ram gets stuck somewhere along the way then it might not make it to the venting holes. So as a test fix the ram in such a position and put the pressure on. If it blows it blows otherwise.. a clean bill of health id say. As for exuasting the high pressure CO2.. make sure to use a falve vent (i.e. 3/2 valve). Just incase the piston doesnt reach the venting position.

Having the holes above the final position of the piston sounds like a better idea than having them below the final resting position. The reason we have them there at the moment is to let the air around the top of the piston move out quicker when I activate it. If I put the holes in the top then I suppose I can get it tested just like any other piston. We use a separate valve for exhausting the CO2.

Thanks for the advice.

Dave

Ive used the method you mention on a (vru old) featherweight.
It did have some advantages, such as reducing the vent time and allowing more flips per second, but the downsides were too numerous and I ditched it (low pressure setup)
I have suggested this before, and will again.
Andy Kane of Kan-opener, and FRA chairman, once offered to test any hydraulic rams if people wanted, if you e-mail him, this may apply to pnematic rams too. The holes are no problem, Im sure the ram can be positioned so they are not used.
Cheers
James

A further question. I have made a full pressure pneumatic ram, and through work I can get it hydraulically tested for free. I would like to take advantage of this offer if it is acceptable. If necessary i can hydrualically test it to 200Bar- is this satisfactory for a 70 bar ram, or must it be pressure tested using gas?

As I understand it, hydraulic cylinders are de-rated by 50% for pneumatic use, and pneumatics parts must be tested to 120% of their operating pressure - so you are OK in terms of static pressure, but when you use it with gas your cylinder will be moving much faster, and your cylinder will have to cope with the dynamic forces when it hits the end of its travel at high speed. Testing this is more difficult, perhaps someone experienced with high pressure pneumatics could help here.

Eddy i dont know myself but at a guess I would say it would be ok as in the rules Rule 8.1.2 states: Components origionally designed for hydraulics use will be de-rated by 50% for pneumatics use.

Maybe I am reading it wrong but surely if you test it hydraulicly to 200bar you can use it at 100 or am I wrong.

Regards
Ian

Eddy,

Its safer to hydraulically test the ram, as the stored energy is much less. This is the industry-standard test method for vessels, so I imagine that it would be fine for rams.

Jeremy

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. It is permitted to mod the ram as long as those mods cannot affect the pressure integrity of the ram. Cushioning is a common mod undertaken to absorb some of the dynamic forces.

You can use gas or fluid to pressure test the ram, if using oil you will need to clean / flush the oil out afterwards.

Paul
FRA Technical Team