Monday, 23 January 2012

Of blastpipes and blowers

I got home late last night, earlier than expected, having completed my weekend's tasks and nipped over to drop some things off with Grandma and Big Grandad.

Yesterday we finally got 'Oliver's blastpipe assembly off. This was not as easy as it should have been, and took about a day and a half in the end. Eventually, it turned out that one of the studs had sheared, and we had to burn it out in order to release it. All the time you have to bear in mind the relative fragility of castings, and the expense of pattern-making and casting of a replacement - not to mention the fact that the engine won't work without it!

When a steam engine is working, steam exhausted from the cylinders comes up the blastpipe and out of the chimney. In the process, it creates a draught in the smokebox, which draws the fire. On top of the blastpipe is the blower (seen here before removal), which creates that draught 'artificially' to prevent the fire from 'blowing back' at the crew, and to draw the fire when the loco is stationary.

Over time, hot oil from the cylinders builds up and bakes onto the inside of the blastpipe, and in the time 'Oliver' has been back in action, it had built up to the point where it was potentially causing excess back-pressure. To avoid the grot off the inside of the blastpipe going down into, and damaging, the pistons, the blastpipe has to be removed in order to chip it off.

So, early yesterday afternoon we finally managed to get the blastpipe out and the blower off, at which I could start chipping the crud off - it was over half an inch thick in places. Some of it split off in slabs, rather like splitting slate - the rest had to be chipped and ground away, and I was seriously encrusted by the time I finished. Three lots of swarfega, two showers and a bath later, and a little remains!

Some time with the whirly wheel on the angle grinder cleaned up the outside of the casting, too - including the all-important flange faces, so it re-seats nicely.

Final task for me (for someone will today be making a new stud to replace the one which met its end) was to make a new gasket. Unlike a car, you can't just pick one up off the shelf, shaped to suit - after all, there are only two 'Britannias' left in existance! A sheet of jointing is therefore the starting point to cut a new one out.

Jointing is pliable but reasonably easily torn. You can cut it with a knife, but on a heavy duty joint like this one, I tend to do it with a hammer. First, you stick bolts, the same diameter as the studs on which the casting sits, through the holes, to keep the sheet in registration.

Then, with a ball pein hammer, you work your way along all the edges to be cut, tapping the edge with the hammer and breaking the jointing cleanly around it. Very quickly you have a gasket of exactly the right dimensions to seal the joint. You then take a picture of your finished work, except I forgot to do that!

I suppose I may as well leave little tips like this on here for you to find in the future. Whilst I would sooner teach you face to face, that is no excuse for me to fail to provide the instruction a father gives his son.

Meantime, 'Oliver' will be back in action next weekend, and out on the main line again soon.

That's the first weekend I've spent at the engine shed for a very, very long time, and the exercise (in both senses of the word!) has done me good. Nose back to the grindstone today, and, speaking of chipping away at greasy filth, responding amongst other things to the CSA...

Love from Daddy

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