Category Archives: The Power Plant

Building the Engine and Boiler
Below are posts related to the building of Arthur Leak’s marine compound steam engine as originally described in Model Engineer magazine and more recently provided via Camden Books (drawings, manual and castings). It will also include the construction of a oil-fired Yarrow watertube boiler, to designs from John King from the SBA (see links on right of home page)

This is the engine that will power SY-Befur, it is expected to produce 10-14HP. These post cover all the construction from Camden’s castings and the addition of pump and alternator assemblies for our particular installation.

A little lubrication

While we wait for the plasma cut boiler plates and housing to arrive I went back to a job that’s needed doing for a while on the engine; the Lubricator.

Approaches to lubrication

There are several approaches to lubricating a steam engine, from a hand-held oil can (tends to be a bit erratic, and you chop the end of the spout off in moving parts) thru oil wicks, to pumped lubrication. I felt that a pumped system was the way to go.

There are 11 bearings that need lubrication in the engine (3 main bearings, 2 big ends, 2 little ends/crossheads, and 4 eccentrics). Actually, there is cylinder lubrication as well, but we are going to deal with that via a separate displacement lubricator which injects oil into the incoming steam (a sort of 19-century “posi-lub”!

There seems to be two approaches to pumped lubrication, either a single pump producing a pressurised rail, and then a set of individual needle-valves or calibrated jets. Or individual pumps for each bearing. Memories of failed cam-shafts on Ford Pinto engines in the 70’s steered me towards the latter approach, so that is what we decided upon.

A V11 pump

jim ewing-style lubricator

A Jim Ewing-style Lubricator

So, the conclusion is a 11-pump lubricator. These are normally arranged as a “V” to reduce the overall length. I have previously built one to Jim Ewing’s design (see pic) which worked very well on the loco. My first plan was therefore to build a set of these and then drive them from a set of cams.

However. for reasons I can’t remember I thought I only needed 10 pumps so, when I drew these up in ViaCAD I drew them with 5 cams driving these in pairs.

FIrst plan - a V10 lubricator - in solid modler

FIrst plan – a V10 lubricator – in solid modler

First plan - a V10 lubricator

First plan – a V10 lubricator

Sprag Clutches

The cams are driven by a pair of “sprag clutches“, which are small needle roller bearings which only allow the shaft to turn in one direction. So, by holding one still in the oil tank and putting the drive arm on the other, one gets effectively a fine ratchet mechanism that will convert any to-and-fro motion into a rotating motion to drive the cams.

Pump Units

However, I concluded two things 1) making 10 (actually 11) of these pumps would take a while and 2) you could buy similar pump assemblies from Lubetec (these are Interlube AC pump units) ready made… So that was what I did – here are some pictures of the final lubricator with 11 of the LubTec pumps fitted – smaller capacity (red) ones for the eccentrics and larger (yellow) ones for the mains, big & little ends….

Onwards….

This slideshow requires JavaScript.

What a lot of holes…

We are progressing with the building of the boiler. The first job is drilling all the holes in the steam and mud drums.

We have 1,236 to do, and so far we have finished 824 of them – it’s boring!

The first 823 were the worst!

The first 823 were the worst!

The next job is to use a countersink bit on a air ratchet (hopefully) to de-burr the inside of all the holes.

Then we will mount the drums into the casing end-plates. and start fitting the tubes… We are using Ashby Welding in Church Crookham to plasma-cut the casing bits from 3mm plate, and they are also cutting the blanks for the drum end covers and the economiser and super-heater headers from 20mm plate.

Here is a picture of the CAD drawings I created to drive the plasma machine…

lifu-housing-componentsv2

lifu-housing-componentsv2

Boiler Begins!

Sorry for the long silence, we have been working hard to relocate to Cumbria and convert the garage into a workshop – with that approximately complete it allows me to get started on the boiler for Befur. So this post concerns itself with this topic. Continue reading

More Engine Work; Valve Setting etc.

For about a year now I have been saying “Yes, the engine is done, apart from a few bits and bobs” – so the other week I found myself waiting for some timber to arrive and decided to just “knock those bits and bobs on the head” – 10 minutes inspecting the engine revealed that there were in fact (at least) 23 jobs still to be done!!! So so far we have spent two weeks reducing this list to 7…. (and deciding to do some much later!) Herewith some notes on some of this activity… Continue reading

Drivetrain and Spline cutting

We have turned one eye to the business of the drive train and prop-shaft for Befur.

I have concluded that I am putting a CV joint in the drive train, to allow the engine to be mounted horizontally, and also going to use a toothed belt drive from the engine to the prop-shaft, so allow me to install the engine off-centre, and improve internal layout.

The “Drivetrain”

Continue reading

Edwards and Feed Pump VIdeoz

Here’s a better video (with iffy commentary) showing the feed and air pumps (and alternator) drive in action.

The Edwards pump is working, but I’m not sure that the flap valves are holding pressure (as it seems to have to start from atmospheric on each stroke…) but clearly the ball valves on the feed pumps are very sound (they actually hold 50psi for hours)…..

enjoy…

A Suitable end to a winter’s engineering!

The plan is to work with the seasons and transition from boat building when it’s warm to mechanical engineering when it’s winter – and we are clearly heading into spring and temperatures in the boat house are becoming tolerable, and suitable for working with Epoxy; however, I was loath to make the switch back to boat building until I had concluded the design and construction of the pump and alternator drive assembly.

This has proven a very slow process, and as my good friend  David Mattingley pointed out there is a world of difference between building something from drawings and designing and building from scratch.

The design process – solid modelers

pump/alternator drive

Isometric of the planned pump and alternator assembly

I used PunchCAD’s ViaCAD 3D to draw the basic arrangement of this assembly, and this solid modeler was a new experience for me having previously only used 2D CAD systems (like Autocad). With this new solid modeling approach you manipulate 3d objects (cylinders, cubes etc.) to construct a computer model of the thing you are planning to build. You drill holes in things (by subtracting a “hole-sized” cylinders from the object) and merge primatives to create more complex shapes (like the alternator and gear box in the attached pic). This approach allows you to see clashes of components and get a good feel for clearances and shape of the final assembly. It requires a very different mindset. When the model is complete it is possible to create dimensioned 2D drawings of each part (although I confess I found it hard to get this feature to provide exactly what I wanted.)

This got me to phase 1, with the worm box, chain-wheels, v-belts and alternator all in position, and running smoothly (although it did not predict that the chain would need a tensioner as the centre distance I had chosen for the chainwheels forced us to fit a chain that was almost exactly one link too long) 😦

The lengthier part of the build/design process was to then mate this assembly to the air and feed pump assembly we completed a month or so back.

Feed Pump Drive

I had decided to use the worm-box output shaft to drive two cranks, each being used to form a scotch crank assembly (see this nice video if you are not familiar with how a scotch crank (AKA Scotch Yoke) works). This meant I could remove the uneven stress on the worm box if we only drive the pumps from one side. It became clear we should mount the pumps over the worm box, to avoid adding too much height to the engine assembly, and so an arrangement with 4 “side levers” running down from the pump crosshead to the scotch cranks seemed right. Mounting the pump assembly required a stiffened plate which I fabricated from some 3mm Brass plate I had in the “stock pile”.

The cranks are fitted to a keyed shaft, and each crank pin is 10mm silver steel. I found some thin section ball races (10mm ID, 15mm OD and 4mm wide) from Bearing Boys, and used two on each crankpin. However, I was unsure of the load capacity of the bearing, and the spreadsheet I had constructed for the pumps suggested that the four bearings needed to support a dynamic load of almost 100lbs (when pumping @ 200psi), and while this theoretically would be shared across 4 bearings, this would require “perfect” conditions. During an initial test I accidentally jammed a plastic mug! into the assembly stalling the engine – this resulted in two of the bearings failing with split outer races. I suspect the jam caused the bearings to be axially overloaded, but none the less this failure was worrying.

I contemplated fitting needle roller races to raise the load capacity, but as an initial “fix” I fitted 3mm thick outer “retaining rings” in silver steel to the bearings to strengthen the outer races… with this fix in place and some hose pipe to prime the pumps I ran a test with a pressure gauge on the feed line, and a 200psi safety valve to regulate the pressure (as you can see we reached over 250psi in practice).

As the video below shows we appear to have a working system (with hints of Tardis – don’t you think!!!) – the variability in pressure is to some extent caused by the safety valve, but also I think the pump valves may be slow to seat…

I feel I can now get on with the “wood work”, with a job well done!!!