# Soft solder for Gas Tanks?



## Nutz-n-Bolts (Aug 12, 2010)

Once my m5x0.5 tap arrives I will be able to finish the last part of a tank I have been building, and I will be able to solder it. Is it ok to use soft solder for this or is there enough strength advantage that I should silver solder it?

And yes, pictures and story to come. I just wanted to get a bit further along before starting a build thread.


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## Charles (Jan 2, 2008)

Silver solder

Here is a prior link with some good advise

Fuel Tank


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## Totalwrecker (Feb 26, 2009)

Soft solder can crack when the cold gas makes everything shrink.... Silver solder is harder like the host metal and can withstand the hot and cold cycles.


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## Nutz-n-Bolts (Aug 12, 2010)

Thanks guys. Looks like its off to buy some new solder sticks. This will be my first shoot with silver soldering. Going to have to get a hand pump too for the hydro test.


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## Shay Gear Head (Jan 3, 2008)

A bicycle foot pump is great because it leaves your hands free for other needed things.


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## steveciambrone (Jan 2, 2008)

If it is your first time silver soldering, practice on some scrap parts to get your technique down. There may be a video on Youtube you might be able to watch. 

How is a bicycle air pump used for a hydro test? It won't pump water or a high enough pressure. 

Thanks 
Steve


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## Semper Vaporo (Jan 2, 2008)

NEVER "pressure test" with "air". NEVER! 

Water is non-compressible, so when using water for a TEST, if there is a failure of the system, all you get is a squirt of water as there will be no energy stored in the water (the squirt will come from the metal container relaxing the stretching from the pressure). If you use AIR (or any compressible gas) then if there is a failure in the system, the energy of the compression will be released with possible catastrophic (DEADLY) results.


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## Michael Glavin (Jan 2, 2009)

Semp is spot on with pressure testing with air, it can be very dangerous without the proper safeguards and knowledge…… 



That said air is a better medium for pressure testing at lower psi numbers as the waters viscosity and surface tension tends to plug small openings that air is impervious too for the most part.
A MAXIMUM of 3-4 psi is all that is required for low pressure air testing, 4 psi air equates to about 14 psi water pressure due to the differences in viscosity.

Michael


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## Nutz-n-Bolts (Aug 12, 2010)

Thanks Steve, I plan to practice a little. 

To the rest of you, Not to worry. I know better than to use air for the test. I'm going to get one of those hand WATER pump kits from Fee-Bay. They make ample pressure for the test. It will be a good investment since I plan to build many more pressure vessels.


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## seadawg (Jan 2, 2008)

Randy, a short tip that you may already be aware of. As the assembly gets larger, it begins to act like a heat sink and you will need more heat near the end of the project than at the begining. I started silver soldering an alcohol wick holder with a propane torch and began wishing for something hotter by the last tube (4 wick holder).


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## Nutz-n-Bolts (Aug 12, 2010)

Thanks for the tip Dave. That makes sense, once pieces are soldered they can then transfer heat much better. I have an oxy/acetylene torch set so I should have plenty of heat. Like Steve suggests, I'll practice a little.


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## xo18thfa (Jan 2, 2008)

Also, be sure to get flux that matches the solder. For silver solder the flux is a white, water based paste. After soldering, clean off the flux leftovers. Citric acid is the best and safest, but a little battery acid in water does the job too


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## David BaileyK27 (Jan 2, 2008)

Randy, I hope your test pump can supply the pressure required for testing gas tanks, here in the UK we test to 300 PSI for Butane and 600 PSI for Propane, you need a good pump and a pressure gauge with at least 50 PSI margin over the test pressure. 
David Bailey


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## Nutz-n-Bolts (Aug 12, 2010)

Thanks Bob, Some form of pickling solution and flux are on my shopping list too. I'm definitely leaning towards the Citric acid. I'm going shopping Saturday morning. 

David, I apologize but I have to disagree with your testing pressures. looking at the link Charles posted above you can see that the highest pressure that could be expected is 107psi. The standard for testing I am going by is test to double the max operating pressure. So, 214psi it is. Are you talking about large tanks or our small models with testing pressures that high?


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## Pauli (Jan 3, 2008)

About pressure testing,

the way I've done it, I use an aircompressor, but fill the vessel / gastank / boiler completely, before connecting the compressor. (Then I add airpressure gradually. Once I reach my desired testing pressure, I hold that for at least 10 minutes, checking that airpressure doesn't lower, or any waterleaks appear. But I think you know that.)

I don't see that using a waterpump to build pressure would be safer or technically better. What do you think?

I built an auxilliary / secondary gastank that I use in the tender of my gasfired Maerklin BR18/ S3/6 locomotive. (This allows refueling during a run, when the primary gastank is to warm to be possible to fill. Info for newcomers  ) Based on that, I urge anyone to really try to rinse the finished gastank insanely well. If I build another gastank, I would consider both filling, and then boiling the filled tank, in citric acid sollution to remove any remains of flux. I thought I rinsed carefully, but I had to unclogg the burner nozzle very annoyingly often after installing. I think remaining minute flux debris was the cause.

Merry Christmas!


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## Semper Vaporo (Jan 2, 2008)

I'll give you a little experiment to try...

Get a package of cheap balloons... get the round kind and try to get enough so that you can sort for size and get several that are very similar.

Build a small 4 sided corral of some sort big enough to surround a filled balloon so you can measure the balloons as you inflate them so they will all be the same size when filled.

Inflate one balloon completely with water, let it settle and let out any entrained air so there are no bubbles when the balloon "just fills" the corral.

Then put it in the sink (or I guess you could hold it in your lap, but that might prove embarrassing later) and take a pin, dart or sharp knife and burst the balloon and note how far the water splashes. The distance the water splashes will be directly related to how much pressure the balloon itself is applying from being distended by the water forced into it.

Now, partially inflate a balloon with water and finish inflating it with air. Strive for a 50/50 measure by volume. Again, make sure the balloon just fits the corral so you know it is the same as the 1st balloon. Burst this balloon and see how far the water splashes. The distance the water splashes will be directly related to how much pressure the balloon itself is applying from being distended by the water and the air forced into it, PLUS the air that was compressed in the balloon to distend it to the same size as the 1st balloon.


I HAVE DONE THIS! And I did it when it was 95 degrees outside and the wetness was a pleasant diversion from the heat!


You may want to do it several times, both with water only filled balloons and with combined water and air filled balloons to get some averages. It does not take much pressure to distend (inflate) a balloon, maybe on the order of 2 to 5 PSIg. The distance the water splashes will be only slightly more, on average, when there is a 50/50 volume of air and water than filled with water only, but it will be a definite detectable difference!

Now, think about using an air compressor to apply the pressure to the water in a pressure vessal being TESTED. You DO NOT KNOW the integrity of the vessal. It might have a weak point that will burst at 1/2 (give or take 100%) of what you expect it to have the strength to withstand.

There are several things to consider in this. What is the "Volume" capacity of the compressor? What is the volume of any attached tank? What is the volume of the hoses/piping between the compressor and the vessal being tested? What is the transfer of air capacity of the hoses/piping between the compressor and the vessal being tested?

Worse case scenario: The compressor has a 300 gallon tank filled to 300 PSIg. There is a 3/4 inch iron pipe from the compressor to the work area (so the noise of the compressor does not disturb people in the shop) and it is 30 ft long. Then there is a 1/2 inch reinforced synthetic material hose connecting the end of the pipe in the shop to test bench. Let's say that hose is 10-ft long.

You SLOWLY open the valve between the compressor tank and the hose to apply 300 PSIg to the water filled vessal being tested. Being as this is a worst case scenario, you have no pressure regulator in the shop to limit the pressure as you open the valve. So you get 300 PSIg in the hose and the air in the hose starts to compress. It will rapidly approach 300 PSIg as the hose distends. You then open the valve at the vessal being tested. Thus applying the full 300 PSIg to the vessal. 

The test vessal will distend some amount due to the pressure. Assume it ruptures. A soldered seam rips or a boss pops out. Water will come out at 300 PSIg, being propelled by the air in the hose, pipe and air tank of the compressor supply system. The amount of pressure supplied by the distended vessal walls and the distended hose are negligable compared to the compressed air.

Have you ever played with one of those toy rockets where you fill the body of the rocket 1/2 full of water and then pump air into it (remember the warning on the instruction sheet "No more than 20 pumps of the hand pump"... ha ha ha... how many of us went to 25... 30... 50!) then you pull the release and the rocket takes off, spewing water all over your hand holding the launcher! (A fun and cooling activity on hot summer days!) If you got the water level right and pumped it right and the release was quick, you might get it to go 25 to 50 feet in the air! (No where near the "HUNDREDS OF FEET" is says on the box!) 

If you were like most of us, you also tried launching it with the rocket full of water and found that you didn't have the strength to pump it more than 3 to 5 times and the rocket would barely fall off the launcher and it was still full of water laying on the ground at your feet. And if you put NO water in it, you could pump it all day and lose count of the number of times you pushed the plunger and when you finally gave up and pulled the trigger it would go maybe 3 or 4 feet in the air in a loud bang and then fall 5 or 10 feet from you.

NOW... think about what happens to your little butane tank laying on the work bench with 300 PSIg pressure on the small amount of water coming out that ruptured seam or now missing boss.


What was that song Elton John sang.... "ROCKET MAAAAAAAAN!"


Near-Best case scenario: No compressor tank at all. VERY short solid pipes from the compressor to the vessal being tested and a pressure regulator between the piping and the vessal being tested.

Turn on the compressor and in two strokes the safety valve on the cylinder blows off the excess pressure (you are wearing hearing protection so you have not injured your ears, best case scenario, remember!). You open the pressure regulator to allow a few pounds of pressure into the test vessal. You increase the pressure until it reaches, say 150 PSIg and seeing as that we are discussing a failure scenario, a seam rips or a boss pops out. You now have a stream of water exiting the vessal at 150 PSIg and the compressor is still running, supplying it continuously until you shut it off.

Granted, the volume of water is small, but I hope it is not aimed at your face.


BEST case scenario: NO AIR! You fill the test vessal with water and have a simple hand operated water pump connected to the test vessal with short pipes. You pump the hand pump once and the pipes and vessal distend due to the pressure. You pump it again and the gauge will register 50 to 100 PSI and after about 1/2 way through the 3rd or 4th strokes and the gauge will be at 150 to 300 PSI.

Since we are talking Failure of the test vessal here, suppose a seam rips or a boss pops out... Your hand on the pump lever will fly forward shoving the last 1/4 inch diameter by 3/8 inch long slug of water in the pump cylinder forward as the distended pressure vessal and pipes contract and force a slug of water just slightly bigger out the opening with a force of 150 PSIg and the pressure is GONE and everything stops. Granted, you don't want your face in the way of the boss or slug of water, but neither will go far with the pressure gone. 

When I test my Aster Mikado boilers, I hold the safety valves down with my fingers and pump the tender pump a couple of times. The guage on the engine goes to maximum and I let it sit a little while. I may have to pump again to keep the pressure up due to the check valves leaking water back to the tender. Then because my fingers are beginning to hurt pressing on the blunted pin sticking out of the safety valves, I let go of the one aimed away from me. The slug of water will hit the ceiling, but it amounts to about 1/8 teaspoon of water and quickly dries. Then I inspect all the seams and fittings using a clean dry tissue (Kleenex) to see if there is any water leakage. I have found leakage at some fittings a couple of times, but never at any seams or bosses in the boiler. I have renewed a rubber gasket at one fitting once, and just tightened the fittings at the others.


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## Nutz-n-Bolts (Aug 12, 2010)

Gee Semper, Every time you explain this, your explanation gets better. Spot on. Thanks for trying to keeping us all safe!


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## Shay Gear Head (Jan 3, 2008)

And longer!


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## Pauli (Jan 3, 2008)

Realistically,

the amount of compressed air available to a rupture, is the amount in the connecting 1/4" x 3feet tube from the compressor. Wich is a very small amount of air. Also, a complete burst, only appearing at higher pressure, showing no leakage at lower pressure, is very peculiar. I found two minor leaks during first testing, and thus dissconnected and resoldered, and went back to pressure testing. Using a foot air pump would maybe also work, but then you might want to attach a check valve and a separate pressure gauge. The reduction gauge on a compressor does a good job in this context, I think. (Also when test running an engine on air - making sure you have taken care of lubrication ;-) )

I don't think evoking catastrophic scenarios unnessessarily helps people enjoying the hobby. No one has ever heard of a gastank exploding, even after a leakage has caught fire (wich is utterly rare).

And I dont want hot steasm in my face. But seriously, also exploding locomotive boilers, sending water and parts flying in the air, seem to be non existant in real life.


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## steamupdad (Aug 19, 2008)

Lets not forget that there is a difference between pressure and volume. A pressure may remain constant but the volume can vary. Example: if a boiler is at 60psi and you crack the throttle open, you have 60psi at the cylinders but the volume (or rate/speed of air/steam flow) is minimul. You get slow speed or very little pulling power. Open the throttle more, your still at 60psi at the cylinders, but now your at faster speed or more pulling power. Not sure if this relevant but thought I'd mention that there is a difference between pressure and volume. This can also work vise-versa. Steady volume with variating pressure.


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## Semper Vaporo (Jan 2, 2008)

ONE MORE TIME!

You are talking about TESTING a completely UNKNOWN pressure vessel. You do *NOT* *KNOW* if the vessel is made of imperfection-free materials or if the construction is without imperfections. Even if you have made this one particular design from the same batch of materials as the previous 100 you have made and you used the exact same techniques, you do NOT "KNOW" that the particular pieces of metal and silver-solder were uncontaminated in their manufacture and are as good as the pieces you used before.

Have you ultrasound tested the metal for internal defects or cracks that you cannot see? Did you even inspect the metal with a magnifying glass to see even visible cracks? Did you verify that the silver solder joints penetrated properly? DO YOU "KNOW" beyond a shadow of doubt that all is well before you apply pressure to the vessel?

THAT IS THE PURPOSE OF THE HYDRO-TEST!!

I will grant you that the chances of an explosion is probably 1 in 100 million, but it seems that people will plop down their hard earned money on that 1 in 175 million chance of winning the lottery so those "odds" must be pretty "good" (?).


When you are done TESTING the pressure vessel, you are then going to put something in it that is more dangerous than compressed air... you are going to put a liquefied gas (Butane) in the tank. The energy of liquefaction is much greater that the energy in just compressed air, but you now KNOW that the vessel can hold the pressure without failing. 

Likewise, if you were testing a boiler, you KNOW that the boiler can contain the pressure of the vaporized water.

You initially test to 2 times the designed *working* pressure limit (not the theoretical limit of the materials) and then you know it can handle the pressure it will typically run at with a 100% margin of safety. Later, when you retest the pressure vessel for integrity, you test to only 1.5 (one and a half) times the designed *working* pressure to KNOW that thermal and pressure stresses have not lowered the integrity of the vessel.


There is also the problem of people reading one thing and extrapolating the notion that if "X" worked for one person, then "Z" (times 2) will be okay, too.


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## Nutz-n-Bolts (Aug 12, 2010)

Hi everybody! I made some progress and thought I would share.... 









The picture above shows all of the parts I currently have ready for the tank. I cut 2 new ends out of 1/8 plate which fit very snugly into the ends of the fitting. I cut some hexagons with the band saw and then drilled a 3/16 hole in the center of each. I chucked up tow nuts in the lathe and the screwed the plate to the face of the chuck jaws and shaped them up. I also went with a bit bigger stay to match the larger center mounting holes in the new ends. It can be seen laying in the bottom of the picture. The brass bar at the top is the start of the top plug. I need to pick up my metric dill bit set from Grainger Monday so that I can drill and tap it for the ronson valve then part the finished cap off of the bar.

Also in the picture are the two bottles of citric acid I bought. Of all places, I found it at Lowe's in the canning supply section. I tried many stores prior. My question now, is what is a good ratio of water to powder for the mix? I'm still looking for that perfect container to store the bath. Can't seem to find a 5x5 x 24 inch Tupperware container.


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## bille1906 (May 2, 2009)

Almost any mixture will work but two or three table spoons per gallon will do the job. If the flux and black oxidation are soft in a half hour, the mixture is strong enough.


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