Condenser Oil Trap for a Small Steam Engine

I needed a small condenser & oil trap for a model steam boat project as small steam engines tend to exhaust as much if not more water & steam from their exhausts as they do steam. This tends to make a mess if you don't contain it, additionally for a boat it is particulary important to catch the oil to avoid polluting your local pond or lake.

The type of steam plant that I have for the boat, takes a fixed amount of gas & water and runs until the gas runs out. This means for each run, it runs for a fairly predicatable amount of time but helpfully, produces a fairly predicatable amount of oil & condensate waste. I measured this from a few test runs, and knowing the space I had available in the boat I was was able to source a length of brass tube of close enough to the correct size.

This project was also a bit of a learning exercise for me as it was my first time making something functional using Silver Soldering. This is similar to soldering for electronics but use solder that melts at a much higher temperature and makes a much stronger joint.

• 100mm x 100mm 2mm Brass Sheet
• 1 1/2" x 16g Brass Tube (This was a bit thick walled but it was all I could get)
• 1/4 x 40 ME Pipe Union
• Easy Flow Flux Powder
• Hard Silver Solder (Wire or Strip)
• Easy Silver Solder (Wire or Strip)
• Pickling Powder
• 15mm diameter Copper Plumbing Pipe 30mm long
• Sandpaper (400, 600, & 800 Grit)

• A saw (I used a Bandsaw)
• A square
• Hammer
• Centre Punch
• Dividers
• Digital Calipers
• A Steel Ruler
• A Tap Wrench

• 1/4" x 40 ME Taper Carbon Tap

• I used a bench mounted disc sander but the same could be achived with a file.

I started by scribing a line the width of the end plates away from a straight edge of the sheet of brass and then dividing this in two. These two rectangles will become the two end plates. I then added a centre line and scribed a line half of the width in from each end. Where these two lines cross will be the centre of the radius for the rounded ends. I used a centre punch to mark this point and some dividers set to half the width of the end plates to mark the rounded ends.

Next I cut out the two pieces, keeping as close to the line as I could. I used a homemade disc sander to finish off the last little bit up to the line and leave a nice smooth curved edge.

I used the same homemade disc sander to square up the ends of the Brass tube that I bought. Not the ideal method but the best that I had available at the time. It was a bit tricky but being very gentle and slowly rolling the tube seemed to help.

Using the previously marked centre point & line I added a mark for the inlet. To ensure the hole will end up only being inside the tube this should be no more than half the internal diameter of the big tube + half the external diameter of the threaded hole from the centre point. I then made a centre mark at this point & drilled tapping size for the fitting I was going to use.

For me this was a 1/4 inch diameter 40tpi ME thread which a quick web search gives the drill size as 5.5mm. I then used a taper tap of the desired size in a hand held tap wrench. This can be quite tricky so if you haven't done it before I would reccommend doing a few trial holes. It is very important to keep the tap square the hole you want to tap.

Shaping two tubes to fit together can be difficult but I used a trick to get the copper exhaust pipe to match exactly to the brass tube. First I used a half round file to remove some material and the place some sand paper over the large brass tube. Holding the copper pipe as square as possible I rubbed it forward & back along the brass tube with with sandpaper which slowly made the exact matching shape in the end of the copper pipe.

I won't go into too much detail on the techniques for Silver Soldering here as that is complex enough for its own turtoral but I will go over the basic outline and how to apply it to this project.

I chose to solder up the condenser in 3 steps. This would avoid having to make a complex holding or jig arrangement to hold all of the parts together, I could just rely on gravity. There is a small risk that the heat from the later joints could melt earlier ones but by being careful I could avoid this.

1. Attach one end plate
2. Align & attach the other end plate
3. Attach the exhaust

First I cleaned the joint using very fine sandpaper (400 grit or finer). I then applied the flux paste everywhere I wanted the solder to go and placed the two parts together making sure the large brass tube was correctly positioned on the end plate.

Next was to apply the heat, wait for the flux to melt and then apply this Silver Solder. This was the largest thing I had Silver Soldered so far and I was glad I made sure I had a sufficiently powerful heat source. I was using a large plumbers gas soldering torch with handheld disposable gas cannister.

Now the first joint was complete, I could turn it over, place the other end of the tube onto the 2nd end plate (making sure it was all cleaned of course) and the align the two. It isn't super critical to get it exact as and misalignment can be corrected with a file later, but the closer you get it first time, the easier it will be.

By using a square on a reasonably flat surface I was able to position the tube so I was happy it was well enough aligned. Don't forget to apply the flux first so you don't disturb the alignment. I then soldered this joint using the same technique as the previous step, the two joints being far enough appart to avoid one melting the other.

This joint was much the same as the rest, clean, apply flux, align the parts, and solder. When you need to solder two joints like this at different times you can use a slightly different, lower temperature Silver Solder to reduce the risk of melting the first joint. You still need to be very careful as you can vey easily overheat the joint and melt everything. In this case I used 'easy' Silver Solder from a jewelers supplier.

When finished soldering I put the whole condenser into a pot of water for a few hours which had suitable pickling powder dissolved into it. Then it was a case of using wet or dry sandpaper (400, 600 & 800 grit) and then polishing with Brasso.

I screwed the pipe union I purchased into the condenser and hook it up to the steam engine to test.