machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment. I read every comment and respond to most. n.b. There is a list of my first 800 posts in my post of 17 June 2021, titled "800 Posts"


A Visit to The Boiler Inspector

My colleague and friend Swen is building a 1″ scale traction engine, and he is about to commence the boiler.  He wanted to discuss some issues regarding the plans with the club boiler inspector.  I had some questions regarding the Trevithick Dredger Engine final inspection, so I tagged along.


Swen (purple T shirt) and Adrian discussing the traction engine boiler plans.

The boiler inspector is a marine engineer, currently working on tug boats, but with a lifetime of experience in ocean going ships.  His personal interest is mainly with steam and other trains.  But he is very happy to watch the progress of older, more historic models, like the Trevithick.  But always the emphasis is on safety.   Safety over historicity, authenticity, etc.   As it should be.

I was interested to note that Australia’s model steam regulations are widely used as the bench mark in other countries.

My current obstacles to final boiler certification are

  1.  The boiler feed pump is not working.  When I described the situation to Adrian he diagnosed the problem as the suction ball valve.  So afterwards I was working on that.  I have attached a sacrificial ball to a brass rod, and given it a firm whack to the seat.
  2. The difficulty getting the boiler pressure up to the pressure to demonstrate that the safety valve is working. Using propane, I can get the pressure up to 22psi, which is adequate to run the engine, but not high enough to make the safety valve release.  Adrian suggested that I reduce the mass of the lead weight, so it releases at 35psi rather than the current 40-45psi.  And to consider lagging the boiler.   The picture from 1819 shows the dredger engine boiler unlagged.  But the Pen-y-darren engine and the “Catch-Me-Who-Can”  and the Cambourne Road loco are all lagged.   So I suspect that Trevithick would have approved if the dredger engines were lagged.   So guess what?   I am going to lag my dredger engine, and I hope that if Richard Trevithick is watching that he will approve.   I will use Australian hardwood, and paint or stain it black.  Or maybe some English oak, if I can find some in my workshop.   The lead ball in my model is much bigger than shown in the 1819 drawings, so I will have no hesitation in making a smaller one.
  3. What is the water volume of the boiler?  I knew that I had to use 2000ml to get the water half way up the water gauge, but I did not know the actual volume of the boiler.  So today I measured it.   Surprisingly, it was 2750ml.   Almost 3 litres!   No wonder it takes 20 minutes to get it steaming!

So, very close to the final inspection.

Meanwhile, there is very little of pictorial interest for this blog.   So I decided to show some of my workshop(s).

Next, in response to reader Tim, I will show my silver soldering and brazing setup.   Then maybe some of my lathes.  Please note that I am not claiming any expertise.  Just interested amateur stuff.  Might be a change from Antarctica hey?


Hydrostatic Trevithick Boiler Test

This is a video showing how I performed the hydrostatic test on the boiler.

The engine is currently being made, but not at the time of the video.

The test is to hold water at double the working pressure of the boiler, for 20-30 minutes, checking for bulging or distortion of any of the components, and any significant leaks.  Any leaks would need to be fixed, but for the boiler certification, as long as the pressure can be maintained for the duration of test, that is OK.

The working pressure of this boiler will be 50psi, but the minimum pressure in the AMBSC code is 60psi, so the hydrostatic test will be done at 120psi.   As you will see in the video, the pressure reached 140psi at times.

In fact, the AMBSC code is formulated in terms of materials and design to cope with 8 times the working pressure, so the safety margin is generous.

The video is taken over 20 minutes.  I ran the actual test for over an hour.

I am afraid that my very messy bench and workshop are evident in the video.  No apologies.  That is just the way that I work.



VR-18-18 Stands for Victoria, Geelong Society of Model and Experimental Engineers, 2018, 18th registered boiler for the club.

So this morning I fired up the boiler with the boiler inspector closely watching.  The gas was turned to maximum, and the water was showing full.

Steam appeared about 10 minutes later and the Sandberg safety valve started popping at 100 psi. Every couple of minutes the safety valve released and the pressure remained in the 97-100 psi range.  This went on for about 20-30 minutes.  All to the satisfaction of the inspector.

He was happy with the standard of the build, the pressure test, the accumulation test, and that all requirements had been met.

The boiler is now certified for 4 years.  There has been a change in protocol about which I was unaware.  The previous certification rule was for 12 months only, and retesting was required for a further 3 years.  So this new rule is much less time consuming for me and the inspector.  He is happy that before the next testing I will have a steam pump and a steam injector installed.


I was so delighted with the result that I treated myself to a trip to the non ferrous metal supplier, and bought a selection of hex brass stock for the workshop.  When I returned to the workshop there were still a few hours of daylight, so I spent the time making the new inspection hatch for the Trevithick dredger engine.  Not quite finished, so no pics yet.

The next step for the boiler is to make and attach the wood lagging and to put on some paint.


Now that the model triple expansion engine is working on steam, I feel able to put it aside, again, and move onto the next project.  The triple is not quite finished.  It needs cylinder lagging, control rods for the cylinder drain cocks, drain tubes for the cylinder drains, and an extra pump for the condenser cooling, and some paint, possibly.

It also needs a boiler.  I would like to exhibit the triple at club demonstrations and public exhibitions, but for that I need a boiler which is certified by our boiler safety authority.  So I intend to make a boiler to AMBSC code, and big enough for the triple or any other engines which I might make in the foreseeable future.

This is what I have in mind….

boiler assembly

This is a copper boiler with a 152mm (6″) diameter barrel, a superheater, gas or coal fueled, and firetubes (most not shown).  The plans call for a 5″ barrel, but I have been unable to find any suitable copper tube, and I have some 6″, so that is what will be used.  I am currently drawing up the plans.

The certification process here in Australia requires the following steps:

  1. Preliminary discussion with the boiler inspector (done)
  2. Submission of 2 sets of plans to the boiler inspector.  If acceptable, one set is signed off and stamped and returned.  The other set is held by the inspector.
  3. Inspection of the prepared components by the inspector prior to soldering/brazing/welding.
  4. Inspection of the firebox and tube assembly after soldering/brazing/welding.
  5. Inspection of the barrel and outer wrapper after soldering/brazing/welding.
  6. Testing the boiler after completion.  This involves a hydrostatic test, at double working pressure for 20 minutes, then a steam test at 10% above working pressure.

If it passes, the boiler is certified for 12 months, after which it must be retested.  If it passes the retest it is certified for 3 years.

The certification process is performed by volunteer inspectors attached to model engineering clubs, and is done at no cost.

However the materials for a boiler like this are quite costly.  I managed to obtain some  copper tube for the wrapper, and bought some copper plate for the firebox and boiler ends on Ebay.  Bronze for the bushes from a local bearing supplier (LG2), and firetube copper tube from local plumbing supplies.  All up, so far, is approaching $AUD1000.  And yet to be factored is the safety valve, various cocks, sight gauge, hand pump silver solder.  And I intend to make and fit a steam driven feeder pump, and possibly a steam injector.

If there is any interest in this project I will post progress notes and photos.  Let me know.