| January/February 1962

  • Gossip from the back shop

  • Gossip from the back shop

I remember when once my morning trek to work was halted as I heard the loud talking of a steam engine down in Hanson's shop. While he had a water brake set up for testing, it had never been in operation while I had been around. This apparatus functions like a Prony brake, but instead of using a brake band around the large drum to tilt the scale when the engine is loaded up, a perforated disk turns within a close-fitting housing through which water is circulated. This makes control much easier with no tendency to bind up. My old friend and master mechanic had just set the double-ported valve on Walsh's 10 horsepower Russell the night before, and was running off some indicator cards to check the overall balance of the engine.

'Do all double-ported valves make that much racket under a good load?' I inquired of Mel while the noise from the stack under the smoke jack in the shop sounded like an entire tribe of African natives beating on large drums. 'Well, quite likely,' he shouted back to me, 'but the double-porting has little or nothing to do with the snort of the exhaust, because the extra valve passage is always under inlet steam and never sees the exhaust port. It just lets the steam into the cylinder quicker at the beginning of the stroke.' Gee, come to think of it, the old boy was right, and this point had never occurred to me before.

As his assistant let off on the water circulation and the engine coasted along more quietly for a few minutes, Mel replaced the indicator cards which he had just recorded and after moving the reverse lever from its present position near center to that at full quadrant, called to Manfred, 'Alright, Manny, let's have the same amount of water again.' I noticed that under these conditions the old girl seemed to bark a bit louder than before, although doing the same amount of work. At the end of this short run, when Mel removed the indicator card with its traces for both ends of the cylinder, I felt again the urge to seek a little more knowledge. 'Well, I know you are not studying X-ray pictures, but what can you see there?' I asked. While Manny shut the. engine down, I trailed Mel over to the desk top on his work bench, where he pulled a planimeter out of its cubbyhole and told me that he was measuring the work load of each end of the cylinder, from which he would calculate the cylinder horsepower. When he had finished his figuring, he turned to me and said, 'Now this may be of interest to you. Notice that we have called for the same given amount of work to be performed under hookup as under full quadrant, and as closely verified by these diagrams. But with hookup at about 40 percent the governor was riding low and running full steam pressure to the chest, while consequently releasing it to the atmosphere at a lower pressure than was possible under maximum cutoff where the governor was throttling the steam to about 70 percent of full pressure under the same load.' 'I don't get what you are driving at,' I puzzled, at this point really wallowing down in my ignorance. ' If you would quit wearing that dumphoozled Derby hat on your noggin,' he began razzing me, 'you would remember that paper discussion we had some time ago when I explained to you that, according to the Rankin cycle, which describes what goes on in a steam cylinder, the efficiency of a reciprocating steam engine is dependent upon amongst other things, the ratio of the steam pressure at admission to that at which release occurs.' As my face reddened up a bit, I had to admit he had me dead to rights there, and now I began to see that under this principle an engine would run more efficiently if it could be hooked up a bit. If many of you fellows to whom I am telling this story are further interested, I will ask old Mel to let us borrow those cards for publication.


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