What comes out the stacks of a steam loco, how and why?
Jul 30, 2020 12:19:03 GMT
Country Joe, dennym57, and 6 more like this
Post by ptc on Jul 30, 2020 12:19:03 GMT
What comes out the stacks of a steam loco, how and why?
A steam loco is a big tea kettle placed on its side. Instead of being a hollow chamber it is full of tubes (flues) which carry exhaust gasses from burning coal or oil from the firebox, in front of the cab, to the smoke-box, below the stack. But how do you get the products of combustion to draft horizontally, then up the stack and not fill the cab with smoke? Answer; the stack is a venturi tube. (Google that one) The stack that you see is only about one fifth the total height. The rest is inside the smoke-box. It is designed for maximum non turbulent air flow. There is also a nozzle at the top of the stack which increase air flow velocity. The air flow is caused by steam exhaust from the cylinders. 4 chuffs per wheel revolution, 8 in the arctic. This airflow produces a vacuum which sucks the coal combustion products, fly ash, smoke, gas through the flues and out the stack at high velocity. It has been said that the exhaust from PRR M1 through star nozzle could be seen to melt low hanging clouds! Exhaust pressure 10-20 PSI. When engine stops the engineer opens an air vent valve and blows compressed air up through the stack to clear the flues. This is the loud hissing sound you hear when you stop and before your engine starts moving. Smoke box vent.
Ok so what causes smoke? Is it good or bad? How is it controlled?
Smoke is bad, legally, and profit-wise. It is caused by the fireman feeding too much coal too fast. Kinda like too much charcoal fluid on back yard grill. There were railroad and gov't smoke inspectors and there was trouble if you got caught.
The stack emits carbon monoxide, sulfur compounds, fly ash (soot), steam and water, and some other stuff, including cinders, hot and cold. This brings me to my next question. Why do engineers wear their hats backwards? Are they would be rap artists?. No, they had to wear goggle to stop the cinders from perforating their corneas.
The engineer had terrible forward vision. Actually scary. He had to rely on fireman to see left side of engine. He had small forward window and no windshield wiper. He is usually seen sticking his head out the window. Try this in your car sometime going 80 miles per hour. So both the forward and side cab windows had deflectors. (wing windows) The cab roof had a deflector at the rear of the cab. Some engines had elephant ears. The Powhatan Arrow had deflectors on the roof ends, to keep cylinders and fly ash from dirtying car ends!
Cab forwards were designed to keep smoke out of cabs since SP had long snow sheds in the Sierra Nevadas.
Well there you have it. Now really impress your friends and humble your enemies!
Until next time....
Your brother in the worlds greatest hobby,
Harry Hieke
A steam loco is a big tea kettle placed on its side. Instead of being a hollow chamber it is full of tubes (flues) which carry exhaust gasses from burning coal or oil from the firebox, in front of the cab, to the smoke-box, below the stack. But how do you get the products of combustion to draft horizontally, then up the stack and not fill the cab with smoke? Answer; the stack is a venturi tube. (Google that one) The stack that you see is only about one fifth the total height. The rest is inside the smoke-box. It is designed for maximum non turbulent air flow. There is also a nozzle at the top of the stack which increase air flow velocity. The air flow is caused by steam exhaust from the cylinders. 4 chuffs per wheel revolution, 8 in the arctic. This airflow produces a vacuum which sucks the coal combustion products, fly ash, smoke, gas through the flues and out the stack at high velocity. It has been said that the exhaust from PRR M1 through star nozzle could be seen to melt low hanging clouds! Exhaust pressure 10-20 PSI. When engine stops the engineer opens an air vent valve and blows compressed air up through the stack to clear the flues. This is the loud hissing sound you hear when you stop and before your engine starts moving. Smoke box vent.
Ok so what causes smoke? Is it good or bad? How is it controlled?
Smoke is bad, legally, and profit-wise. It is caused by the fireman feeding too much coal too fast. Kinda like too much charcoal fluid on back yard grill. There were railroad and gov't smoke inspectors and there was trouble if you got caught.
The stack emits carbon monoxide, sulfur compounds, fly ash (soot), steam and water, and some other stuff, including cinders, hot and cold. This brings me to my next question. Why do engineers wear their hats backwards? Are they would be rap artists?. No, they had to wear goggle to stop the cinders from perforating their corneas.
The engineer had terrible forward vision. Actually scary. He had to rely on fireman to see left side of engine. He had small forward window and no windshield wiper. He is usually seen sticking his head out the window. Try this in your car sometime going 80 miles per hour. So both the forward and side cab windows had deflectors. (wing windows) The cab roof had a deflector at the rear of the cab. Some engines had elephant ears. The Powhatan Arrow had deflectors on the roof ends, to keep cylinders and fly ash from dirtying car ends!
Cab forwards were designed to keep smoke out of cabs since SP had long snow sheds in the Sierra Nevadas.
Well there you have it. Now really impress your friends and humble your enemies!
Until next time....
Your brother in the worlds greatest hobby,
Harry Hieke
