Steam Locomotive

Posted by PITHOCRATES - November 13th, 2013

Technology 101

The Steam Locomotive was one of the Few Technologies that wasn’t replaced by a Superior Technology 

Man first used stone tools about two and a half million years ago.  We first controlled fire for our use about a million years ago.  We first domesticated animals and began farming a little over 10,000 years ago.  The Egyptians were moving goods by boats some 5,000 years ago.  The Greeks and Romans first used the water wheel for power about 2,500 years ago. The Industrial Revolution began about 250 years ago.  James Watt improved the steam engine about 230 years ago.  England introduced the first steam locomotive into rail service about 210 years ago. 

In the first half of the 1800s the United States started building its railroads.  Helping the North to win the Civil War.  And completing the transcontinental railroad in 1869.  By 1890 there were about 130,000 miles of track crisscrossing the United States.  With the stream locomotives growing faster.  And more powerful.  These massive marvels of engineering helped the United States to become the number one economic power in the world.  As her vast resources and manufacturing centers were all connected by rail.  These powerful steam locomotives raced people across the continent.  And pulled ever longer—and heavier—freight trains.

We built bigger and bigger steam locomotives.  That had the power to pull freight across mountains.  To race across the Great Plains.  And into our cities.  With the chugging sound and the mournful steam whistle filling many a childhood memories.  But by the end of World War II the era of steam was over.  After little more than a century.  Barely a blip in the historical record.  Yet it advanced mankind in that century like few other technological advances.   Transforming the Industrial Revolution into the Second Industrial Revolution.  Or the Technological Revolution.  That gave us the steel that built America.  Electric Power.  Mass production.  And the production line.  None of which would have happened without the steam locomotive.  It was one of the few technologies that wasn’t replaced by a superior technology.  For the steam locomotive was more powerful than the diesel-electric that replaced it.  But the diesel-electric was far more cost-efficient than the steam locomotive. Even if you had to lash up 5 diesels to do the job of one steam locomotive.

The Hot Gases from the Firebox pass through the Boiler Tubes to Boil Water into Steam

The steam engine is an external combustion engine.  Unlike the internal combustion engine the burning of fuel did not move a piston.  Instead burning fuel produced steam.  And the expansion energy in steam moved the piston.  The steam locomotive is a large but compact boiler on wheels.  At one end is a firebox that typically burned wood, coal or oil.  At the other end is the smokebox.  Where the hot gases from the firebox ultimately vent out into the atmosphere through the smokestack.  In between the firebox and the smokebox are a bundle of long pipes.  Boiler tubes.  The longer the locomotive the longer the boiler tubes. 

To start a fire the fireman lights something to burn with a torch and places it on the grating in the firebox.  As this burns he may place some pieces of wood on it to build the fire bigger.  Once the fire is strong he will start shoveling in coal.  Slowly but surely the fire grows hotter.  The hot gases pass through the boiler tubes and into the smokebox.  And up the smoke stack.  Water surrounds the boiler tubes.  The hot gases in the boiler tubes heat the water around the tubes.  Boiling it into steam.  Slowly but surely the amount of water boiled into steam grows.  Increasing the steam pressure in the boiler.  At the top of the boiler over the boiler tubes is a steam dome.  A high point in the boiler where steam under pressure collects looking for a way out of the boiler.  Turned up into the steam dome is a pipe that runs down and splits into two.  Running to the valve chest above each steam cylinder.  Where the steam pushes a piston back and forth.  Which connects to the drive wheels via a connecting rod.

When the engineer moves the throttle level it operates a variable valve in the steam dome.  The more he opens this valve the more steam flows out of the boiler and into the valve chests.  And the greater the speed.  The valve in the valve chest moved back and forth.  When it moved to one side it opened a port into the piston cylinder behind the piston to push it one way.  Then the valve moved the other way.  Opening a port on the other side of the piston cylinder to allow steam to flow in front of the piston.  To push it back the other way.  As the steam expanded in the cylinder to push the piston the spent steam exhausted into the smoke stack and up into the atmosphere.  Creating a draft that helped pull the hot gases from the firebox through the boiler tubes, into the smokebox and out the smoke stack.  Creating the chugging sound from our childhood memories.

The Challenger and the Big Boy were the Superstars of Steam Locomotives

To keep the locomotive moving required two things.  A continuous supply of fuel and water.  Stored in the tender trailing the locomotive.  The fireman shoveled coal from the tender into the firebox.  What space the coal wasn’t occupying in the tender was filled with water.  The only limit on speed and power was the size of the boiler.  The bigger the firebox the hotter the fire.  And the hungrier it was for fuel.  The bigger locomotives required a mechanized coal feeder into the firebox as a person couldn’t shovel the coal fast enough.  Also, the bigger the engine the greater the weight.  The greater the weight the greater the wear and tear on the rail.  Like trucks on the highway railroads had a limit of weight per axel.  So as the engines got bigger the more wheels there were ahead of the drive wheels and trailing the drive wheels.  For example, the Hudson 4-6-4 had two axels (with four wheels) ahead of the drive wheels.  Three axles (with 6 wheels) connected to the pistons that powered the train.  And two axels (with four wheels) trailing the drive wheels to help support the weight of the firebox.

To achieve ever higher speeds and power over grades required ever larger boilers.  For higher speeds used a lot of steam.  Requiring a huge firebox to keep boiling water into steam to maintain those higher speeds.  But greater lengths and heavier boilers required more wheels.  And more wheels did not turn well in curves.  Leading to more wear and tear on the rails.  Enter the 4-6-6-4 Challenger.  The pinnacle of steam locomotive design.  To accommodate this behemoth on curves the designers reintroduced the articulating locomotive.  They split up the 12 drive wheels of the then most powerful locomotive in service into two sets of 6.  Each with their own set of pistons.  While the long boiler was a solid piece the frame underneath wasn’t.  It had a pivot point.  The first set of drive wheels and the four wheels in front of them were in front of this pivot.  And the second set of drive wheels and the trailing 4 wheels that carried the weight of the massive boiler on the Challenger were behind this pivot.  So instead of having one 4-6-6-4 struggling through curves there was one 4-6 trailing one 6-4.  Allowing it to negotiate curves easier and at greater speeds.

The Challenger was fast.  And powerful.  It could handle just about any track in America.  Except that over the Wasatch Range between Green River, Wyoming and Ogden, Utah.  Here even the Challenger couldn’t negotiate those grades on its own.  These trains required double-heading.  Two Challengers with two crews (unlike lashing up diesels today where one crew operates multiple units from one cab).  And helper locomotives.  This took a lot of time.  And cost a lot of money.  So to negotiate these steep grades Union Pacific built the 4-8-8-4 articulated Big Boy.  Basically the Challenger on steroids.  The Big Boy could pull anything anywhere.  The Challenger and the Big Boy were the superstars of steam locomotives.  But these massive boilers on wheels required an enormous amount of maintenance.  Which is why they lasted but 20 years in service.  Replaced by tiny little diesel-electric locomotives.  That revolutionized railroading.  Because they were so less costly to maintain and operate.  Even if you had to use 7 of them to do what one Big Boy could do.


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Feedback Loop Control System

Posted by PITHOCRATES - October 30th, 2013

Technology 101

Living through Winters became easier with Thermostats

When man discovered how to make fire it changed where we could live.  We no longer had to follow the food south when winter came.  We could stay through the winter.  And build a home.  As long as we could store enough food for the winter.  And had fire to stay warm.  To prevent our dying from exposure to the cold.

There’s nothing like sitting around a campfire.  It’s warm.  And cozy.  In large part because it’s outside.  So the smoke, soot and ash stayed outside.  It wasn’t always like that, though.  We used to bring that campfire inside the home.  With a hole in the roof for the smoke.  And families slept around the fire.  Together.  Even as some fornicated.  To propagate the species.  But that wasn’t the worst part about living around an indoor campfire.

Your distance from the fire determined how hot or cold you were.  And it was very hot by it.  Not so hot away from it.  Especially with a hole in the roof.  Worst, everyone got colder as the fire burned out.  Meaning someone had to get up to start a new fire.  The hard way.  Creating an ember.  Using it to start some kindling burning.  Then adding larger sticks and branches onto the kindling until they started to burn.  Which was a lot harder than turning the thermostat to ‘heat’ at the beginning of the heating season and forgetting about it.  Then turning it to ‘off’ at the end of the heating season.

A Feedback Loop Control System measures the Output of a System and Compares it to a Desired Output

Replacing the indoor campfire with a boiler or furnace made life a lot simpler.  For with a supply of fuel (natural gas, fuel oil, electricity, etc.) the fire never burned itself out.  And you never had to get up to start a new one.  Of course, that created another problem.  Shutting it off.

Boilers and furnaces are very efficient today.  They produce a lot of heat.  And if you let them run all day long it would become like a hot summer day inside your house.  Something we don’t want.  Which is why we use air conditioners on hot summer days.  So heating systems can’t run all day long.  But we can’t keep getting up all night to turn it off when we’re too hot.  And turning it back on when we’re too cold.  Which is why we developed the feedback loop control system.

We did not develop the feedback loop control system for our heating systems.  Our heating systems are just one of many things we control with a feedback loop control system.  Which is basically measuring the output of a system and comparing it to a desired output.  For example, if we want to sleep under a cozy warm blanket we may set the ‘set-point’ to 68 degrees (on the thermostat).  The heating system will run and measure the actual temperature (at the thermostat) and compare it to the desired set-point.  That’s the feedback loop.  If the actual temperature is below the desired set-point (68 degrees in our example) the heat stays on.  Once the actual temperature equals the set-point the heat shuts off.

The Autopilot System includes Independent Control Systems for Speed, Heading and Altitude

Speed control on a car is another example of a feedback loop control system.  But this control system is a little more complex than a thermostat turning a heating system on and off.  As it doesn’t shut the engine off once the car reaches the set-point speed.  If it did the speed would immediately begin to fall below the set-point.  Also, a car’s speed varies due to terrain.  Gravity speeds the car when it’s going downhill.  And slows it down when it’s going uphill.  The speed controller continuously measures the car’s actual speed and subtracts it from the set-point.  If the number is negative the controller moves the vehicle’s throttle one way.  If it’s positive it moves the throttle in the other way.  The greater the difference the greater the movement.  And it keeps making these speed ‘corrections’ until the difference between the actual speed and the set-point is reduced to zero.

Though more complex than a heating thermostat the speed control on a car is pretty simple.  It has one input (speed).  And one output (throttle adjustment).  Now an airplane has a far more complex control system.  Often called just ‘autopilot’.  When it is actually multiple systems.  There is an auto-speed system that measures air speed and adjusts engine throttles.  There is a heading control system that measures the aircraft’s heading and adjusts the ailerons to adjust course heading.  There is an altitude control system that measures altitude and adjusts the elevators to adjust altitude.  And systems that measure and correct pitch and yaw.  Pilots enter set-points for each of these in the autopilot console.  And these control systems constantly measure actual readings (speed, heading and altitude) and compares them to the set-points in the autopilot console and adjusts the appropriate flight controls as necessary. 

Unlike a car or an airplane a building doesn’t move from point A to point B.  Yet they often have more complex control systems than autopilot systems on airplanes.  With thousands of inputs and outputs.  For example, in the summer there’s chilled water temperature, heating hot water temperature (for the summer boiler), supply air pressure, return air pressure, outdoor air pressure, indoor air pressure, outdoor temperature, outdoor humidity, indoor temperature (at numerous locations), indoor humidity, etc.  Thousands of inputs.  And thousands of outputs.  And unlike an airplane these are all integrated into one control system.  To produce a comfortable temperature in the building.  Maintain indoor air quality.  Keep humidity levels below what is uncomfortable and possibly damaging to electronic systems.  And prevent mold from growing.  But not keep it too dry that people suffer static sparks, dry eyes, dry nasal cavities that can lead to nose bleeds, dry and cracked skin, etc.  To prevent a blast of air hitting people when they open a door.  To keep the cold winter air from entering the building through cracks and spaces around doors and windows.  And a whole lot more.  Far more than the thermostat in our homes that turns our heating system on and off.


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