Valves, unions, and piping?

Bill,
for our steam donkeys we used the PM fittings, some of them threaded, some silver soldered. For my recent project I tried the smallest 1/8" castings combined with 5/32" thin walled tubing from K&S, see:

http://www.mylargescale.com/Community/Forums/tabid/56/forumid/11/postid/81054/view/topic/tpage/2/Default.aspx

I drilled the elbows etc. 1/8" and turned a shallow 5/32" step to insert the tube. For bending I used the tube bender from Dubro after countless failures with other bending devices.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXRS90&P=FR

I usually make my own valves, just for fun .
Regards

Sorry Henner but I have to make a correction to your posting.  We used COLES fittings on the Donkeys.  Scale elbows and tees for 5/32" OD pipe to be precise.  I would know since I was the pipe fitter on the project.  I chose Coles fittings because they were pre-machined with scale tapered threads, and I wanted to screw the pipe work together where it made sense to do so.  Here is a picture of the plumbing on the donkeys before paint.


 


 The donut shaped thing is the throttle valve body.  You can also see the white pipe dope that i used to make sure the threads were steam tight.


 
Regards,
 

Bill: Yes. Brass bushings can undergo a chemical change. The zinc in brass can leach out over time , leave the bushing brittle and prone to cracking. Bronze does not do that, so there is no point in taking the risk. Bronze bushings are available from Sulphur Springs Steam Models carry bronze bushings in Model Engineering threads. 40 or 32 threads per inch. They are at: http://www.sssmodels.com/ Follow the links to engine parts and boiler fittings.


PM Research has bronze bushings too and it appears they come in Model Taper Pipe thread and Model Engineering thread. They are at: http://www.pmresearchinc.com/store/home.php


I use all ME, 40 thread taps and dies and make my own stuff. So here is a thing I just learned. It just so happens that 3/16" and 1/4" Model Taper Pipe are 40 Threads per inch. 3/16" and 1/4" Model Engineering are also 40 threads per inch. According to PM Research they are interchangeable even tho MTP is tapered and ME is straight. Henner or Eric may have tried this and know the answer. My guess they are and that loctite or teflon tape would ensure a steam tight fit just fine.



Looking at Eric's picture closely, it looks like he silver solders the pipes and screws in the fittings. I bet he uses a threaded fitting, drills it out to pipe diameter, solders it to the pipe and leaves the threads in place for other purposes.

Your bushing count looks good. When you build your boiler, it may not be a bad idea to add an extra bushing or two to the boiler and just plug them. Maybe one half way down in the water and one up high in the steam area. You might want to add a whistle, feed water clack or something later on. It is too much brain surgery to add another bushing after the boiler is done.


Bob

Bill: Here are some photos of a locomotive boiler I built a few years back. This is way way way more complicated than what you described, but it least shows all the steps. Your fittings are all on the outside, screwed into bushings which is very straight forward. On this one I put the throttle box and other stuff on the inside. Flat plates for the boiler ends simplify construction a lot. Careful and patient use of a hand file will do all the work I did on the lathe. The backhead plate fits on the end of the boiler shell. This is real easy to do because there is no fitting work. Just oversize it and trim off the excess after it is soldered on. The front tube plate is inside the boiler shell. That requires some fairly close fitting, but is do-able by hand. Copper is a difficult material to drill. It loves to get "grabby". For safety, clamp the copper sheets down securely to a piece of plywood using wood screws and washers. Clamp that to your drill press table. Some guys use those sheet metal step drills with good success. Or you can "chain drill" larger holes, knock out the center and finish up with files.

Silver soldering is kind of an art. But with the right torch and starting off simple, it's not hard to learn. Planning the sequence of steps is important too.

Draw up a sketch of your boiler and post it.

http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Backhead%20Plate%201.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Boiler%20Assy%201.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Boiler%20Assy%202.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Boiler%20Assy%203.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Boiler%20Assy%204.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Boiler%20Assy%205.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Boiler%20Assy%206.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Boiler%20Assy%207.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Boiler%20Assy%208.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Boiler%20Assy%209.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Firebox%201.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Firebox%202.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Firebox%203.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Firebox%204.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Front%20Tube%20Plate%201.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Front%20Tube%20Plate%202.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Throat%20Plate%201.JPG
http://1stclass.mylargescale.com/xo18thfa/Boiler%20Build/Throat%20Plate%202.JPG

Bob

Posted By Cap'nBill on 02/23/2009 2:59 PM
Thanks for the info/tips, guess I missed the PM bronze. My plan here is to only thread the boiler connections and just drill and S.S. the piping this should be adequate for the 10-30 psi I'll be running. The extra bushing(s) makes since. Seems the best way to do this is have everything ready and silver solder the whole thing at once. Seems to me doing this piecemeal is inviting problems! Bill

You want all the parts cut and fitting up correctly, but want to silver solder in stages. Little parts like the boiler bushings your can do 2 or 3 at a time. Big jobs like the boiler end plates, just 1 at a time. That's a hot chunk of copper you are dealing with. Re-orienting it while its hot to get to another joint is not an easy thing to do. You want to concentrate on one thing at a time. It is better to let it cool down, clean it up again and do the next step. Each time inspect the joint.


What you are worried about is re-heating the part and having a previous joint melt and fall apart. That can happen, but most of the time there is enough friction fit between the parts they are mechanically held together. Boiler bushings, maybe pop lightly with a center punch to stake them in place. The solder on the previous joint may melt a little, but it won't fall apart.


Silver solder most guys use has a silver content of 45% and melts at 1160 degrees. It requires the use of a flux to chemically clean the joint as you heat. You have to mechanically clean the joint with steel wool or fine sandpaper first. The flux is a water based paste. The flux goes thru stages as you heat the part. That is helpful to know. Take a strip of copper, clean it, smear on some flux and drop on a bit of solder wire. Heat very slowly with the torch. The water in the flux burns off and leaves a white powder caked on. The flux starts to turn brownish black, but is still basically solid. The flux starts to melt, it has kind of a dark clear glassy look. Then the copper undernieth gets very bright and shiney. At this point the solder is almost ready to melt and flow. Add a little more heat and the solder will flow. Sometimes it does'nt. You need to have a little scratchrod ready. Scratch thru the molten solder on the copper then it will flow. Don't add anymore heat. You are in business.


The flux has a max temp of about 1400 degrees. Adding too much heat will burn the flux and it won't work. The key to silver soldering is a large, low temperate flame. A MAPP torch would for small parts, but a propane-air rig works best. Oxy-Acetylene is no good. They are way too hot and way too pin-piont. You can burn the flux and maybe burn a hole in the copper.


Soldered joints need cleaning to remove the leftover flux residue. When the cools, soak it bath of 10% sulfuric (battery) acid and 90% water. Some folks use citric acid rather than battery acid, I've not tried it. Rince the part under running water and rub the joint with a brass brush. It will cean up like a shiney new penny. Inspect the joint under a magnifying glass just to make sure the solder went all the way.


Send me a PM with your mailing address and I will send you a photo-copy of a silver soldering course.

Bob