Potential reasons for a poor steaming engine - its not fun to run a steamer when you are having trouble keeping the pressure up. I have been asked at different times why an engine is a poor steamer. Here are some things I would look at if an engine is not steaming well. Leaks in the smokebox If the smokebox door does not seal tightly on the smokebox or the smokebox does not seal tightly on the front of the boiler or there are any holes that allow air to enter into the smokebox, air from outside the smokebox will enter into the smokebox through these leaks instead of coming up through the fire. The blower and blast nozzle may be properly set, but the partial vacuum they create will draw air in through the leaks instead of drawing it through the fire. Steam leaks in the smokebox Leaks from steam lines (blower, lines to cylinders, blast pipe/nozzle) or from tubes or tube sheet will fill/minimize the partial vacuum that is created in the smokebox so less air will be drawn through the fire. Leaks in the firebox Leaks from flues, staybolts, sheets, seams can fill the firebox with steam which will minimize the amount of air that can be drawn in through the fire as it will partly fill/minimize the partial vacuum that is created in the smokebox. If a leak is bad enough, water can put out the fire or severely dampen the fire Blast nozzle not the right size If the blast nozzle is not the right size, the blast may not fill the stack completely to create the best draft or may be too strong or too weak. It seems for coal burners the best blast nozzle diameter (single port blast nozzle) is 14-18% of the piston diameter and for oil 1822% of the piston diameter. Blast nozzle not centered in stack If the blast nozzle is not centered in the stack, the exhaust may not fill the entire stack which can create poor drafting Not enough space between the blast nozzle and the petti-coat If the blast nozzle is too close to the petti-coat, the draft can be severely minimized even if it is centered and is the proper size blast nozzle. I have found that 2-3 between the the blast nozzle and the petti-coat works well on 1:8 steamers Boiler is scaled up If the boiler is full of rust and scale, the heat transfer from the fire through the sheets to the water can be greatly reduced Tubes are dirty If the tubes are dirty the heat transfer can be greatly reduced along with reducing the volume that can pass through them. If I remember correctly, 1/32 of carbon has the same insulating qualities as 3/8 of lime scale. If carbon is left in the tubes, over time/use the carbon can become hard and will really take a scrubbing to remove. Not enough air entering the fire If the fire is not getting enough air steaming qualities can be reduced. For a coal burner the space between the grate bars can be increased (on the 2-4-0 the grate bars are 3/16 wide with 5/16 space between them. The 2-8-2 and 4-6-0 have 1/4 thick bars with 5/16 space between them). On an oil burner, air openings can be added at the back of the oil pan Too much air is entering the fire I have seen this more on oil burners or propane than with coal. If too much air enters the fire not all of it will be heated so cool air will be heading through the tubes. This will cut down on the steaming qualities and thermal shock the firebox and flues and can shorten their life. Boiler is not designed properly I have seen this on engines that have been built in the 30s, 40s, 50s that are not built from kits or designs that have been developed by suppliers to the hobby. These engines are built and designed to the best ability of the builder, which at times can lead to designs that are less than ideal. The boiler may be too small for the demand that is placed on it, or the firebox is too small, etc. Stack is not designed properly This is one that I have seen with engines that are not built from kits or designs that have been developed by suppliers to the hobby. The engine I saw had a stack that was too small in diameter (it also looked like it was too small) so the volume of gasses that needed to pass through the stack could not. Poor timing If an engine is poorly timed, the distribution of the steam wont be right and the engine can waste steam and use a lot of steam due to poor timing.
Posted on: Mon, 15 Sep 2014 01:17:45 +0000
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