soldering a cracked brass cylinder

[jon hill 3Participant @jonhill3]

Hi

I am restoring an old paraffin blowlamp and discovered that the pump tube was cracked. I was thinking on soldering the fracture however I don't know how to clean inside the crack so the solder will take. Any ideas, degrease & vineger pickle for example?

[jon hill 3Participant @jonhill3]

blowlamp repair

[Bo’sunParticipant @bosun58570]

Hi jon,

Even if you could successfully solder the pump tube, I doubt the piston would seal adequately.

I would contact "Base Camp" and see if they have a spare..

[Martin Johnson 1Participant @martinjohnson1]

I would be very wary of using it after repair. Pressurised parafin, red hot srfaces and a dodgy repair – what coould possibly go wrong? Even if you don't intend to use it, others might if it is sold on.

Martin

[IanTParticipant @iant]

Well, I've never done this but I would think it is do'able.

Off the top of my head (without going down the shed and looking) I think both my old blowlamps have removable pumps. So the tube could be dis-assembled from the main blowlamp body and given a good physical clean before a suitable dunk in citric acid. I would use silver solder (445 0.5mm wire) and (dependant on the tube thickness) try to clean the crack sides by cutting a 'V' with a sharp diamond-end graver tool. Place small pallets (bits) of solder along the crack (to avoid too much solder getting into the barrel) and lot's of flux. If you don't use too much solder, the inside should be fine. Oh, and heat from the other side of the crack, fanning the flame (don't linger).

It's pumping air, so I wouldn't think it's a dangerous repair to do. If you don't get a complete seal, then it's going to be a bit harder to pump up to pressure but mine have leather seals that are pretty forgiving. Of course you may get a little spread of silver solder on the outside but if you just want something to polish for the mantlepiece, then don't try to repair it.

Perhaps not the best place to start for a beginner though Jon – especially if you've not brazed anything before. Thin brass is pretty easy to melt with high heat, in fact so are thick bits too. I've managed to do both. 

Regards,

 

IanT

Edited By IanT on 30/05/2023 14:50:04

[jon hill 3Participant @jonhill3]

Hi Ian,

thanks for the advice. You are right the pump is detachable and the tube is very thin perhaps 0.8mm or less. However it does have some type of solder librally applied in various places. Perhaps indicating a previous sticky closed one-way valve, hence fractures and previous soldering?

Would soft lead solder be ok to make a reasonable seal as I expect this was used before?

Thanks also Bo'sun and Martin comments duly noted.

I will try to upload a picture later.

[Bo’sunParticipant @bosun58570]

Hi jon,

Soft solder might work (most joints on these devices appear to be soft soldered}. But bear in mind you're creating a butt joint. Pump tubes are usually a scant fit in the tank boss, and if that's the case you may not end up with much solder holding the outside of the split together.

[IanTParticipant @iant]

Soft and hard solders don't usually mix that well Jon.

If someone has already been trying for a repair with soft (probably leaded) solder, then a different approach may be required. If you can "sweat" a thin brass (or tinplate) cover over the crack, it will probably not look as pretty but it should hold. Soft solder won't hold very well in terms of a simple 'butt' joint but a patch will have a much larger surface to bond with the tube (being a 'lap' joint). It's generally easier to do too, provided you tin both surfaces carefully before attempting to sweat them together.

Again we are going for 'working' rather than 'mantlepiece'

Regards,

IanT

[IanTParticipant @iant]

PS Bo'un is thinking 'internal' pump – I was imagining an 'external' pump. Mine (Primus) screw on the top and the pump body sticks out of the blow-torch top – it's not inside…

If the pump body/tube has to pass through/into a fitting on the body, then a patch probably won't work unless the fitting is the generous side and any gap can be taken up by the seals….

Regards,

IanT

[Tim StevensParticipant @timstevens64731]

A further problem relates to the reason for the split. If a soldered joint has come undone, what state are other joints in? And if it was not a soldered joint, then suspect 'season cracking' – common in the old days when horse manure was common, as brass can be attacked by ammonia fumes. If so, other cracks will exist, waiting to open up when you are not looking.

'Season cracking' was a serious problem in the trenches of WW1. Cartridges were regularly affected.

Sorry – Tim

Edited By Tim Stevens on 31/05/2023 11:19:36

[jon hill 3Participant @jonhill3]

Here is a picture of the pump tube that sits in to the tank, external half cropped out. I came out of a Burmos 1 pint blowlamp. If you examine the left end close to the non return valve there is a small hairline crack. Apologies if not to visible in the photo. The solder looks like it may have been re-applied as a patch. Im not sure if it is lead or silver solder? On the reverse pic I filed away some of the old repair solder to check for further cracks, but I couldn't see any.

Is this evidence of 'season cracking'? Perhaps your right Tim if so this blowlamp could be 1940's or older…

[Tim StevensParticipant @timstevens64731]

The soldering you can see here – round both ends of the pump tube – is soft solder. The extra blobs at the left end are likely to be the result of the flux, which can allow the molten solder to spread about. This means that with a small heat supply it should be easy to remove the end cap, and the rest of the tube, in stages. First, though, remove the pump piston assembly and wash the whole tube to remove traces of old paraffin.

If you are not familiar with the 'tricks of the trade' here, a small propane blowlamp (as used in kitchens to scorch the tops of some puddings) should serve to melt the solder, and it will help if you have smeared the surface of the old solder with a paste flux (be sure that your flux is for soft soldering with lead solder).

As soon as the end cap comes loose from the tube, tap it firmly down on a wood block, and this will shake off most of the old solder, ready for putting it back together. The tube which is split can then be removed, and this should only need a brief extra splash of the flame, as it will still be fairly hot. It should be possible at this stage to clean up the offending end including the crack, and using more flux, resolder the end cap, filling the crack in the process. A patch should not be necessary, but if you need one, use very thin copper (easier to form to shape) and hold it in place with fine wire twisted round, as you will use the torch in one hand and the solder in the other. If resoldering is not possible measure the tube diameter and length to see if a replacement can be found. If not, it should be possible to get a new tube bent from a flat sheet and hard soldered, but finding the right tools or the right craftsman or -woman is not at all easy. Or even a tube turned from a solid brass bar.

Or, if you are lucky, you might find someone on the forum who would have a go at it for you (but don't hold your breath …)

Regards, Tim

Edited By Tim Stevens on 31/05/2023 16:04:10

[Bo’sunParticipant @bosun58570]

Hello jon,

A patch might be your best bet. Whether that's solder or thin brass will depend on whether the assembly will fit back into the tank. Looking at it I think it will be tight. You'd also need to be careful not to unsolder the end cap.

I think i'd also like to understand what the apparently previous repairs were for. You may have more than one crack.

As to your original question. I would suggest a solvent cleaner (something like brake cleaner) and a sharp tool to create a minute vee groove along the crack.

Hope this helps. Good luck.

[bernard towersParticipant @bernardtowers37738]

Out of interest what are the tube dimensions?

[jon hill 3Participant @jonhill3]

Hi Bernard

brass tube is 3/4" OD x 0.675" ID approx as tube is slightly oval from a hard life. Its one piece with the tank nut soldered in the middle.

[bernard towersParticipant @bernardtowers37738]

Jon have sent you a pm

[Chris GunnParticipant @chrisgunn36534]

Jon, if it is any help I have brass tube 3/4" o/d by 19G or .042" thick wall, which is close to what you need, I can send a bit if you would like to replace the old piece. Chris Gunn

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