Chatham Steam have continued with a huge amount of work on the boiler, much of it repetitive, and the boiler now has all of its small and large tubes fitted.  As the tubeplates are not perfectly parallel to one another, each tube has to be measured and cut to length to fit its intended location in the boiler. Once all the tubes are in place, they are expanded at both ends to fit the tubeplates snugly.  At the firebox end, a small length of tube is left projecting through the tubeplate, allowing the end to be turned over or beaded. This process helps to prevent the end of the tube overheating and burning away, by providing a large area of contact with the tubeplate through which the heat can be dissipated.  The beading process is quite lengthy, as each section of tube can only be deformed slightly. A tool is wound round the tube several times, increasing the bend on each pass until the tube end is turned back through 180º to face the tubeplate. A seam weld is then made between the tube and the tubeplate, which should ensure that there are no leaks.

The Fusible Plugs were finally removed from the top sheet of the firebox, after copious amounts of heat had been applied. There are six fusible plugs in all, three at the front and three at the rear.  We had noticed grooving corrosion around the plug holes on the fire side of the plate, but fortunately once the plugs were out, the water side of the plate proved to be sound. The area around each plughole was built up with weld, and dressed back to give a smooth finish. Finally the plugholes were re-tapped to clean up the threads and a new set of fusible plugs have been purchased.

The function of a fusible plug is basically simple.  If the water level in the boiler should fall so low that the top of the firebox is not covered, then a central core in the plug will melt, allowing the boiler to vent into the firebox “alerting the crew”, as the saying goes.  One problem with the original design of plug was that as soon as the lead first melted, the flow of steam from the boiler would cool the remaining lead again restricting the hole through which the steam could escape. These new plugs are of a more modern design with a central brass insert held in place by a lead collar.  When the lead melts, the brass plug is ejected and leaves a large diameter hole through which the steam can escape.  We hope we’ll never have to find out if they work!

The joint face on the Regulator Valve body, where it attaches to the main steam pipe in the boiler, has been dressed and the body bolted into position in the boiler.  This joint is critical, as it is on the ‘cylinder’ side of the valve; any leak here will allow steam directly into the cylinders.  The intention is to check this joint as part of the hydraulic test, as we will need to know about any problems as soon as possible.  The face for the Belly Plate has been similarly dressed and the plate fitted.  Also at Chatham, materials have been delivered for a start to be made on the manufacture of the superheater elements; that’s another 160 tubes to go in the boiler!

Back at Toddington, apart from preparing parts and materials for delivery to Chatham, we have spent some time overhauling the regulator valve assembly.  This has a piston with a cast iron piston ring, which was seized in the valve.  We had mistakenly thought that the valve had been overhauled early in the restoration, but this obviously was not correct. After soaking in penetrating oil for several weeks, we were pleasantly surprised to find that the ring came free and the assembly was found to be in very good condition. However, close inspection revealed a groove in the valve face.  This was removed by machining the face back to good metal, and the faces were then lapped to get as good a seal as we can.

A lot of work has gone into salvaging our set of forty superheater clamps. Rust and scale were removed with chipping hammers, the faces were machined and finally sent for shot blasting, which removed the last of the stubborn corrosion and gave a very good finish.

We have continued the long job of making the blanking plates so the boiler can be pressure tested.  Sixteen plates have been delivered to Chatham, some of which will be fitted to the boiler permanently. Only the blanking plate for the blow down valve remains to be supplied.  Once the pressure test is complete, the temporary plates will not be needed again until the first boiler overhaul, so we will have to make sure they are well greased and stored away safely where we can find them!

Whilst the boiler is at Chatham, we are taking the opportunity to have some of the external piping made.  On top of the firebox, there is a pipe which takes steam from the external shut-off valve to the manifold on the boiler backhead. Chatham Steam are making this pipe and we have made a new pair of pipe flanges to be welded on to the ends.  The main pipe faces of the shut-off valve have been re-machined to create a smooth surface.

In the machine shop, we are pleased to report that the last parts required to complete the injectors have been made.  The water overflow valves (or Flap Valves) have been completed and they now have to be fitted to the injectors.

We were pleased to receive delivery of a complete driver’s steam brake valve, fully machined and fitted up. This valve attaches to the side of the Brake Ejector, the body of which is making good progress off-site. Machining this valve body is a long and complicated process, as the valve contains steam cones similar to those in the Injectors, and these have very fine tolerances.

Meanwhile, the Chimney and Petticoat Pipe have been collected from their storage locations and sent off-site to be machined.  We hope to deliver the complete assembly to Chatham for them to fit permanently to the smokebox.

If you would like to get involved with this project, especially by taking out shares in our Company to keep the restoration going, please contact me via the website.

John McMillan