2250 disco conversion with metric valve screws

[chopperjoe]

Hello,
the topic has been discussed here many times and i only need a short answer.
i made a discovery modification on a 2250 tube.
in the usa, the screw size (inch) is different than in europe (metric).
the valve is screwed on the right and left with 2 screws M5 12.9 and at the bottom with M4 12.9.
the filling adapter is from a discovery.
is this conversion safe with 2000psi?

[rsterne]

The Disco uses three 8-32 screws of unknown material and is designed for 2000 psi.... If these are replaced by three low-profile high-tensile screws of 140Ksi the screws are good to 3000 psi, provided the holes in the tube are drilled accurately, so that all 3 screws take equal load.... 8-32 screws have a thread root diameter of 0.125".... Metric screws that are 4mm x 0.7mm have a thread root diameter of 0.118", which is slightly smaller, but 5mm x 0.8mm have a root diameter of 0.152".... Metric 12.9 screws are about 180Ksi (stronger than the upgraded Disco screws I mentioned), so a 4mm x 0.7mm Grade 12.9 should be the equivalent of the 8-32 of 140 Ksi.... Since 2 of your screws are larger, your installation should, at least in theory, be fine, particularly at only 2000 psi.... assuming you have the screw head set down against a flat spot on the Disco valve, as intended, and the screw head taking the load on the tube wall, as per the way the valve is installed in a Disco....

Whether that is actually the case will depend on how accurately you drill the holes in the tube.... All 3 screws must share the load, ie the screw heads must all touch the back of the hole in the tube at the same time.... Regarding the 2250 tube, if the tube has the safety warning "roll stamped" into it, in the area subjected to pressure, you should exercise caution, because that weakens the tube.... Probably OK, but something to be aware of.... Please note, I am NOT an Engineer, and this is my opinion only.... YOU are responsible for the ultimate safety in any gun you modify....

Bob

[lizzie]

Moving to the darkside...

[chopperjoe]

thank you for the detailed advice.
is it allowed to post a picture of my work or privately to you?
I realize that everyone is responsible for their own work. no one gives a guarantee that other people will work.
the tube is operated at 1500 psi and secured with 1.8k.
I will never go above 1.8 psi with tubes I build myself.
at this pressure the rifle is quiet and the power is enough for me. in my 3 discovery rifles i have 9 high-strength bolts from bill.
Andy