I’m back in Wales for a few days and to keep up the momentum of progress I figured I’d set myself a small project, something that doesn’t take up too much space or need too many tools – making some injectors to replace the whitemetal ones with the NuCast 74xx. By the time I’d packed the reference books, tweezers, pliers, components, lamps, soldering iron etc I might as well have brought the whole tool box, but that’s another matter.
Whitemetal kits and etched kits are completely new territory for me, so for about a year before I bought a soldering iron I read, read and read so more. Not that it changed much, I still didn’t feel confident enough to even open the wrapper on the Dean Goods chassis, certainly not the High Level Pannier I’d bought eagerly at ScaleForum months ago, still sat neatly packed in its box… time was the main factor, I needed a clear head and some hours set aside to have a go. Now I’ve got a bit more free time there are no more excuses left. Soldering iron has been bought, Whitemetal kit attempted. No turning back now!
I’d first heard of Iain Rice’s Building Whitemetal Locomotives and Etched Loco Construction through Geoff Forster’s blog Chronicles of Penhydd and I managed to find them both very cheaply second hand. As well as explaining the whole process extremely clearly and with some humour from time to time, it’s the level of scratch built detail that really captured my attention – vacuum pipes (with pipe couplings!), backheads, washout plugs and so much more. It was the injectors that caught my eye though as these are nearly always poorly reproduced in plastic. So here goes, an attempt at creating one of these small Iain Rice masterpieces.
A few months ago the components were collected:
- 1/16″ Brass Capilliary Tubing for the Injector body
- 0.75mm Copper Wire for the steam and water pipes
- 1mm Copper Wire for the Top feed and Overflow pipes
- 16BA and 14BA washers and nuts for the fittings and valves
Before starting however I realised I had no idea what all these mysterious pipes actually did. So a bit of reading up was the first job and thankfully the Bluebell Railway have a full description of the process, documented when they replaced the injectors on 9017:
Steam from the boiler, and water from the tank or tender, pass through a stop valves (taps) controlled by the fireman. When he wishes to increase the level of water in the boiler he turns on the water and steam valves.
Initially water passes into the injector by gravity, where it lifts the hinged combining cone flap, pushes down the overflow valve and runs out of the overflow pipe onto the ground. When the steam valve is opened, a jet of steam escapes from the steam cone. This jet has a high velocity, which it imparts to the surrounding water. At the same time the cold water starts to condense the steam jet. During condensation the volume of the steam is vastly reduced, so a partial vacuum is formed which (a) draws more water from the tank, (b) closes the overflow valve, and (c) shuts the hinged combining cone flap. The mixture of condensing steam and cold water continues to gain speed as it travels through the combining cone. It emerges from the small end of the combining cone as a jet of hot water. It then travels across the gap and into the divergent delivery cone. Here the speed of the jet is reduced, but its pressure is increased sufficiently to lift the delivery clack (non-return valve) and flow into the boiler.
To help get my head around the various pipes, valves and their purpose I put a 3D model together in Sketchup. This is based on the 74xx, though there is an additional thinner pipe from the water inlet valve which goes into the cab – I’m guessing this is how the fireman controls the water inlet from the tanks?
74xx Injector for possible 3D Print
Just getting the thing drawn on paper was a challenge, its the kind of device that no matter how many times I look at it I spot another pipe I’d not seen before, or then looking at it in reverse, on the opposite side of the tank might as well be the first time I’ve seen it. A few sketches and the 3D model helped though and I think I’ve now grasped the concept!
For a test I’ve started out with just the basics – fitting 2 types of wire to the capillary tube and fitting a washer and nut. Straightforward enough I thought, before I started to employ every tweezer I owned and still needed an extra hand. After a while of remelting all the solder and the whole thing falling apart for the 10th time, I switched tactics – drown the whole unit in flux, melt the solder onto the new item to introduce and quickly jam it in place before the solder hardens.
Or alternatively, tomorrow I’ll try to do the whole lot in a 10th of the time with super glue (I’m sure it will still be a challenge though!)
Or, I’ll 3D print the body and still use the wire for piping…
Injector test build
Injector test build