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Success!

Joined: March 9th, 2010, 1:28 am

September 2nd, 2012, 4:41 pm #1

I got it working and holding pressure after realizing I soldered the wrong fitting on. The threads on the fitting were slightly coarser than those on the gauge(at 500PSI the gauge shot out of the fitting...). Went and got a bronze screw-on cap and soldered it on(no pics of it), and now the gun holds pressure!
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Last edited by chaldeman1984 on September 2nd, 2012, 4:44 pm, edited 1 time in total.
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Joined: February 17th, 2010, 3:30 am

September 2nd, 2012, 6:04 pm #2

made from a lead/tin alloy runs from about 4400-6700 psi depending on the alloy.... Most run about 6000 psi.... Just eyeballing from that photo, it looks like the area of the solder joint is significantly smaller than the area of the end of the gauge.... The force on the end of the gauge (0.11 sq.in.) at 1000 psi is about 110 lbs, at 1500 psi it would be 165 lbs.... If the gauge and fitting came off, they would become a projectile with lethal capalities.... If there were cracks or voids in the joint, the surface area subject to the pressure (and hence the force trying to blow off the fitting) would increase, perhaps doubling just before failure.... Said cracks would also reduce the area of solder taking the load.... If the load exceeds ~6000 psi of the remaining solder area, the joint will fail....

The questions that come to my mind are.... How good is the solder?.... How good is the joint?.... Is the adhesion of the solder to the brass stronger than the solder itself?.... Do you really want to find out?....

Bob
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Joined: April 28th, 2010, 12:23 am

September 2nd, 2012, 6:10 pm #3

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Joined: March 9th, 2010, 1:28 am

September 2nd, 2012, 6:54 pm #4

made from a lead/tin alloy runs from about 4400-6700 psi depending on the alloy.... Most run about 6000 psi.... Just eyeballing from that photo, it looks like the area of the solder joint is significantly smaller than the area of the end of the gauge.... The force on the end of the gauge (0.11 sq.in.) at 1000 psi is about 110 lbs, at 1500 psi it would be 165 lbs.... If the gauge and fitting came off, they would become a projectile with lethal capalities.... If there were cracks or voids in the joint, the surface area subject to the pressure (and hence the force trying to blow off the fitting) would increase, perhaps doubling just before failure.... Said cracks would also reduce the area of solder taking the load.... If the load exceeds ~6000 psi of the remaining solder area, the joint will fail....

The questions that come to my mind are.... How good is the solder?.... How good is the joint?.... Is the adhesion of the solder to the brass stronger than the solder itself?.... Do you really want to find out?....

Bob
when the gauge blew off the fitting at high pressure it hit me directly in the abdomen, and didn't even bruise me or anything. Also, the current set up only has a pin-hole through to the actual body tube, the restriction created there is probably why the gauge didn't hurt me when it blew off.
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Joined: March 9th, 2010, 1:28 am

September 2nd, 2012, 7:09 pm #5

made from a lead/tin alloy runs from about 4400-6700 psi depending on the alloy.... Most run about 6000 psi.... Just eyeballing from that photo, it looks like the area of the solder joint is significantly smaller than the area of the end of the gauge.... The force on the end of the gauge (0.11 sq.in.) at 1000 psi is about 110 lbs, at 1500 psi it would be 165 lbs.... If the gauge and fitting came off, they would become a projectile with lethal capalities.... If there were cracks or voids in the joint, the surface area subject to the pressure (and hence the force trying to blow off the fitting) would increase, perhaps doubling just before failure.... Said cracks would also reduce the area of solder taking the load.... If the load exceeds ~6000 psi of the remaining solder area, the joint will fail....

The questions that come to my mind are.... How good is the solder?.... How good is the joint?.... Is the adhesion of the solder to the brass stronger than the solder itself?.... Do you really want to find out?....

Bob
I spent three days practicing for this joint on a damaged 392 tube. I would solder it on with a specific type of solder(I tested four types)then see how much it took to break the joint with a hammer. I used the very last method I tried on the final joint: The contour of the body tube ground into the fitting with a round stone in a die-grinder, filing the edges to get some adhesion on the sides of the fitting, roughing up both surfaces with emery cloth, coating the surfaces with flux, tinning each surface, letting them cool again, roughing up the tinned layers and adding more flux, clamping with a c-clamp, pre-heating with the torch until the tinning on the surfaces melted, and finally soldering all around with acid-core plumbing solder.

With the method above, I had to hammer repeatedly, and the joint did not fail until the body tube was compromised as well. I had to hammer until the fitting and tube were so dented up that the solder sort of folded and finally cracked.
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Joined: February 17th, 2010, 3:30 am

September 2nd, 2012, 7:20 pm #6

when the gauge blew off the fitting at high pressure it hit me directly in the abdomen, and didn't even bruise me or anything. Also, the current set up only has a pin-hole through to the actual body tube, the restriction created there is probably why the gauge didn't hurt me when it blew off.
doesn't reduce the pressure or the force, just the flow AFTER a failure.... I'm glad you didn't get hurt, it could have been much worse, IMO.... I know a fellow who removed the fill fitting from a Disco because he thought it was empty (the gauge said zero).... It blew the fill fitting and the wrench through his drywall ceiling and broke his eardrums.... fortunately it didn't cut his hand/wrist....

All I'm saying is be careful, you don't have any mechanical connection, you are relying 100% on the integrity of the solder joint to prevent the gauge/fitting assembly from departing from the tube....

Bob
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Joined: March 9th, 2010, 1:28 am

September 2nd, 2012, 7:33 pm #7

If I hadn't done all that experimenting with my messed up tube...i'd probably not have trusted it, and I'd have had my dad braze it. I still might later If I get an oxy/propane setup.
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lhd
Joined: November 22nd, 2002, 10:41 pm

September 2nd, 2012, 10:33 pm #8

Get some silver solder and a MAP gas tank ... you can use a propane type torch and do a good strong joint. Silver solder, when dome well, using good silver solder flux, is VERY, VERY strong.

I suggest using a purpose-made steel nipple with the correct inside thread and no feedhole in it, then shape the side to be brazed to fit the airtube very closely. Braze it where you want on to the airtube, then drill a tiny feedhole, say 1/64" thru both nipple and airtube. It won't come back off.
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Joined: March 9th, 2010, 1:28 am

September 2nd, 2012, 10:50 pm #9

My dad refused to braze it. He said since I've already soldered lead/tin on it that it's "contaminated" and that supposedly silver solder wont stick. I'm trying to convince him to do the other side instead, but idk how that'll go. Wait, did you say that with this "MAPP" gas you can use a regular air-venturi type torch to braze with? like it'll get hot enough without an oxy setup? I could do that myself...I found a %50 silver brazing rod digging around the shop the other day...
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Joined: February 17th, 2010, 3:30 am

September 3rd, 2012, 12:48 am #10

with the higher temperatures required.... and not melt the solder between the barrel/breech and the tube?.... Isn't that just soft soldered?....

Bob
Last edited by rsterne on September 3rd, 2012, 12:49 am, edited 1 time in total.
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