XS60C PCP Repeater project

[Kailua]

I had asked if I applied epoxy to permanently screw in the tube into the receiver and was advised that there was still a chance of failure if the threads weren't matched right. 
So if I were to epoxy the tube and epoxy couple of screws through the receiver penetrating the tube.  While leaving enough room for a long modified screw driver to loosen the valve nut and push the valve out through the back of the receiver.  Would that be something that might work?

[stalwart]

Paul, if anyone can make that work, I suspect it would be you. Check your dimensions and placement with Our Beloved (I mean that) Safety Officer... and go for 1.

My suggestion to simply cut 3/4" off the tube, and re-thread it larger, is all I can feel safe recommending. The part overlap is so overkill, properly fitted, that the quality of the tube material and the cap nut's strength are the next questions to answer.

[rsterne]

^X2.... If the threads in the receiver are in good shape, a shortened tube, custom threaded to match the receiver, is overkill in terms of the tensile (end) loads on the tube.... It still isn't as good as a Thru-tube setup, because the thinned area of tube where the threads end is under pressure, and well.... it's thinner than the rest of the tube.... My son's gun has a stock FD-PCP tube, albeit with good fitting threads.... so that should give you an indication of my level of confidence of that setup using a 1500 psi fill.... I do love him, BTW....

Bob

[stalwart]

LOL... I believe you do.

I can tell you who's motives I don't trust: Go to the Pismo Beach dunes any weekend, and you will see little kids, without helmets, riding around on race-prepped Quads. Someone is just BEGGING for it... and, it isn't those kids.

[rsterne]

Yeah, we had a Dad with son on board his Quad doing Wheelies down Main St. in front of our Motel the last long weekend here.... so I know exactly what you mean....

Bob

[Kailua]

Paul, if anyone can make that work, I suspect it would be you. Check your dimensions and placement with Our Beloved (I mean that) Safety Officer... and go for 1.

My suggestion to simply cut 3/4" off the tube, and re-thread it larger, is all I can feel safe recommending. The part overlap is so overkill, properly fitted, that the quality of the tube material and the cap nut's strength are the next questions to answer.


[/quote

Paul, if anyone can make that work, I suspect it would be you. Check your dimensions and placement with Our Beloved (I mean that) Safety Officer... and go for 1.

My suggestion to simply cut 3/4" off the tube, and re-thread it larger, is all I can feel safe recommending. The part overlap is so overkill, properly fitted, that the quality of the tube material and the cap nut's strength are the next questions to answer.

Thanks Eric and Bob,
From what I have and what was suggested.  I am guessing I should be safe at receiver connection.  Must have gotten a little paranoid.  If it wasn't for the guidance from you folks and others here on the GTA I probably would be into building sling shots.

[rsterne]

Yet another attempt at getting the tube of my FD-PCP to seal to the receiver....



I made an extended valve front end.... The ID is drilled and tapped to 16mm x 1.5mm to fit the valve, with a 1/2" ID spring seat to fit the tapered spring that is 1.5" from the back end.... The rest of the valve is drilled through to 13/32", the same as the ID of the large end of the spring.... Therefore, there is tons of flow into the valve, without having any slots in the sides.... The extension sticks out about 1/2" past the end of the receiver, and has an O-ring groove for a #113 Quad Seal, like the one I will use between the valve halves (shown).... There is a slot on the front to snug the two halves together.... The back half of the extension is 0.743" to fit nicely in the inside of the receiver, and the front half is machined down to 0.737" to slide easily into the tube.... The O-ring is past the threads in the tube, and so seals where the tube is full wall thickness.... This puts the threaded part of the tube only in tension, there is no pressure against that portion where the wall is thinner, an added safety benefit.... I sincerely hope this will stop my son's gun from leaking, which has plagued it ever since new....

Bob

[QVTom]

Elegant solution Bob

[rsterne]

Here is the receiver with the extended valve fitted....



Now to thread the tube into place, fill it, and hopefully tomorrow it will still be full.... Cross your fingers....

Bob

[Kailua]

Did it again Bob
That is such a simple solution.  I am not sure anyone else would think of it.  Which is amazing!!!
 

[stalwart]

Elegant

That is precisely the word for it.

[avator]

The guy is not human...
Bob, couldn't something similar be done with the other end of the tube?

[StevenG]

LOL... I believe you do.

I can tell you who's motives I don't trust: Go to the Pismo Beach dunes any weekend, and you will see little kids, without helmets, riding around on race-prepped Quads. Someone is just BEGGING for it... and, it isn't those kids.

Just about every year we lose a kid on a snowmobile that way. Dad puts him in front, gets a few beers in him and hits a tree. Tree on one side, dad on the other, both closing in real fast, you do the math.

[StevenG]

Rsterne, I think we should all chip in and get you Rosetta Stone for Mandarin.

A couple phone calls and you could change the whole industry. If I get a vote your first call should probably be about that extended valve.

[rsterne]

Well, I think I got it ! .... I filled it and topped it last night to 1500 psi, and this morning it is at 1410 psi, and the shop is about 20* cooler, so that is likely just the effect of the charge cooling.... I'll leave it today and see if it stays the same (or even increases a whisker).... I also need to shoot a string and may need to readjust the RVA because the tapered valve spring, although it has similar seat pressure, may not close exactly the same.... so I may need to adjust the preload to get my original velocity and shot count back....

The way I did my gauge mount in the front, the O-ring is behind the threads, so it's on the full thickness of the tube already.... similar to a Disco fill fitting.... The problem with using higher pressures on the front is not the threads (initially), but the flange on the retaining nut, which is too thin to have a proper safety margin at 3K.... If you stay with CO2 pressures (1900 psi at 120*F, remember) it should be OK, although not over-designed....

Please note, this does NOT change any problem associated with the threads pulling apart and launching the tube out of the receiver (which should be a non-issue).... The end load is essentially still the same.... Well, not quite, because it is now based on the ID of the tube instead of the OD/pitch diameter of the threads, which drops it from ~900 lbs. to ~650 lbs.... but the threads still have a large axial load in tension, so have to be in good shape.... However, it does significantly improve the safety margin of the tube itself, because the thin wall below the threads is no longer pressurized.... If the valve extension was made longer, say over 3/4" (1 diameter), it would also make it almost impossible for the tube to fracture at the end of the threads if somebody fell on the gun, because the extension would brace the tube to prevent bending right at the end of the receiver where the last thread is.... However, the longer you make it, the more volume you lose in the reservoir.... I lost about 5 cc with mine....

Bob

[avator]

The way I did my gauge mount in the front, the O-ring is behind the threads, so it's on the full thickness of the tube already.... similar to a Disco fill fitting.... The problem with using higher pressures on the front is not the threads (initially), but the flange on the retaining nut, which is too thin to have a proper safety margin at 3K.... If you stay with CO2 pressures (1900 psi at 120*F, remember) it should be OK, although not over-designed....
Got it.
Thanks

[rsterne]

Ding-dang poppet started to leak (out the barrel) as soon as I test fired it.... I guess I didn't clean the inside of the tube well enough and a bit of grit got lodged in the poppet.... sooooooooooo it comes apart yet again.... 

Bob

[vigilandy]

Ding-dang poppet started to leak (out the barrel) as soon as I test fired it.... I guess I didn't clean the inside of the tube well enough and a bit of grit got lodged in the poppet.... sooooooooooo it comes apart yet again.... 

Bob

Turns out Bob is human after all....   

Seriously though, I almost missed the VERY good discussion here re the air tube threads on the FDPCP.  I will be degassing and checking mine to see how tight/loose everything fits together.   

[Kailua]

Ding-dang poppet started to leak (out the barrel) as soon as I test fired it.... I guess I didn't clean the inside of the tube well enough and a bit of grit got lodged in the poppet.... sooooooooooo it comes apart yet again.... 

Bob

Turns out Bob is human after all....   

Seriously though, I almost missed the VERY good discussion here re the air tube threads on the FDPCP.  I will be degassing and checking mine to see how tight/loose everything fits together.   

That is one good idea.  Maaaybeee  the GTA staff might want to post a sticky on precautions on the FDPCP and or other pcp safety measures.  Like inspecting the tube threads and following fill pressure requirements.  I even remember someone saying his fill hose was not connected properly and the hose went flying when filling from a tank.  Also what ever else one can think of.  So yes I have been told many times how dangerous HPA can be.  Maybe what happened this time and thank god no one was injured was a blessing.  Not saying or not knowing what happen to the FDPCP but like others have mentioned it could happen to any PCP airgun and a safe practice guideline might help future failures. JMO

[stalwart]

Turns out Bob is human after all....   

Well, if you think about that... it's pretty flimsy evidence. Gunk could have come out of the pump.

I remain unconvinced.