GOSSIP FROM THE BACK SHOP

GOSSIP FROM THE BACK SHOP

By FRANK J BURRIS

Content Tools

35640 Avenue F Yucaipa, Calif.

This incident involves a rather unexpected happening in the course of engineering, in which I, as an innocent bystander but nevertheless interested, was to witness what at first hand might be considered as backward progress. But I was reminded that not everything that turns up in mechanical development is necessarily a great stride ahead. At least as we look back on some of these events today, we dislike thinking that some of these diesel and combine outfits are anything but the works of the devil. But what I am about to relate happened many years ago so my yarn may be viewed in the understanding of things as we knew them then, -or at any rate thought we did.

Upon this particular occasion I stopped by the doorway of old Mel's shop and was interested upon seeing Manfred, his right-hand assistant, clearing the heavy wooden packing crate off from a new simple cylinder and valve assembly which the freight man had just delivered that morning. Along the roadway side entrance to the shop was Harold Ferguson's 25 horsepower Case with the Wolff setup about half disassembled. 'What is going on here, anyhow?' I inquired as the nice new cylinder casting burst into full view. 'Well, it looks like we aren't going compound any more with this old kettle,' replied Manfred. Mel was just finishing turning down an old salvage piston to fit the new bore, and as his lathe came to a stop he shut down the old chugging gas engine which powered the line shaft for all the heavy shop tools, and chimed in, 'Yes, Harold can't work this steamer over half capacity on that 34-inch separator. For the last two years he is getting about as much economy out of his coal wagon as we are out of turning these line shafts all the time; but someday we are going to get some of these new-fangled individual electric motors on this machinery and get connected up to the power line in this town, like the newspaper did here a few months ago.'

'But what has all this to do with this boiler?' I interjected, failing to see what electric motors had to do with a compound traction engine only four years in the field. 'Hmmm,' replied Mel, 'you must not have read that Swingles' Handbook I loaned you last winter. Somewhere along about chapter six I recall that it mentions that under light loads a compound engine will tend to waste fuel instead of conserve it.' 'Gee whiz,' I came back, 'Steam is steam, isn't it?' 'Yes,' said Mel, 'but it all depends upon what you do with it. Now, there is what is called a closed-expansion loop between the high and low pressure cylinders, where the exhaust steam from the high pressure end has a chance to expand about an additional two-hundred percent against the low pressure piston. But if the high pressure exhaust is down around 40 pounds pressure, there is a good chance that this pressure will drop to atmospheric at about half-stroke. From there on to the end a slight vacuum may be created; or at least there will not be enough work performed in this loop to even run the engine alone over this portion of the stroke. Now even this is not too much of consequence in that old cross-compound standing out in the back lot. But the deficiency is multiplied in the case of this Wolff job because in this type of tandem connection there results too long a path in the port passages from the single valve to the high-pressure cylinder ends. This particular volume is about twenty percent of that of the high-pressure cylinder. So when the single valve opens to allow a full cylinder of steam, if we are working the old girl properly, to pass on to the low pressure cylinder the first thing this steam sees is a twenty-percent reduction in pressure just filling up the long port passage. There is no inter stage receiver, and the port had just finished exhausting the low pressure steam, so all this work is lost. And if the old girl is working light, the sin alone is compounded.

'Golly,' I budged in, 'it looks like we should have independent high and low pressure valves, with short steam passages as possible, and a variable cutoff on the high-pressure cylinder with a fixed cutoff on the low end,' 'You stick around awhile,' replied Mel,, 'and I will put you to work helping Manfred around here. Yes, this is the cheapest and simplest way to get some compounding, but the Winnipeg tests last year showed that you are doing a bit of good thinking. The economy of this type of compound is only marginal at full load, and is hardly worth the bother and fuss on medium and lighter work. Harold will get plenty of good work out of this animal when we get her reassembled and all tuned up. I think he will give you these old cylinders for that drag weight you were looking for last week.'