Their PCP pistols use the same tubing and I remember Crosman saying the tubes were pressure tested to two or three times working pressure.
Maybe they said working pressure of 2k because that's what the valve was designed for and beyond that valve lock occurs. I've seen people use the stock retention screws and fill assembly at higher pressures and wanted to know if it was safe.
Since the Disco valve retention screws are only #8-32, I'm afraid...
March 29 2012, 10:20 AM
...that claim is just plain wrong - which would be a little disturbing considering the context.
And before you ask, perhaps a machinist will correct me, but I'm prettysure you can't drill and retap the valve body #8 holes for #10 screws - not and end up with decent threads. That's because the major diameter of #8-32 threads is (much) larger than the tap drill used for #10-32s.
This message has been edited by pneuguy on Mar 29, 2012 10:23 AM This message has been edited by pneuguy on Mar 29, 2012 10:21 AM This message has been edited by pneuguy on Mar 29, 2012 10:21 AM
Because the thread pitch and form are the same, it's relatively easy to move up one size and still have good threads. I prefer to hand-ream the 8-32 thread hole to near the 10-32 minor diameter, then hand tap, being careful to engage the existing thread. No reason the new threads shouldn't be decent. The tap will establish the new major diameter.
That said, I have no idea whether increasing the screw size is a good idea, or will provide some greater margin of safety. Shear failure of the screws is only one of the possible failure modes. In the industry I work in, shear failure of the fasteners is the preferred failure mode; oversize fasteners and enlarged holes may result in bearing failure of the base material (ripping the holes out, or cracking around the holes), especially if the hole enlargement isn't done well.
If I were worried about failure, I would hydrotest the assembly to at least 4500 psi,then disassemble and carefully inspect the tube, screws, cap, valve, screw holes, etc., then, if no problems, reassemble and retest. If I were really worried, I would destructively test the assembly to see what it could take (which Crosman likely did at some point) and use the failure pressure to establish the working pressure. Crunching numbers based on material specs will only get you in the ballpark; destructive testing establishes the true baseline. But then, you would need some new parts.
Just a guess as to what the tube is made from/tested...
March 30 2012, 10:14 PM
...and its just a guess. Could be that there is a real reason for the Disco tube to be rated at 2K reguardless of the strength of the retention screws. Could be that they under estimate the tube's ability.
NONE of us know, and in not knowing, is probably best to take the factory recommendation to heart.
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