Manual Hand Brake, Dynamic Braking and George Westinghouse’s Failsafe Railway Air Brake

Posted by PITHOCRATES - July 17th, 2013

Technology 101

Getting a Long and Heavy Train Moving was no good unless you could Stop It

Trains shrank countries.  Allowing people to travel greater distances faster than ever before.  And move more freight than ever before.  Freight so heavy that no horse could have ever pulled it.  The only limitation was the power of the locomotive.  Well, that.  And one other thing.  The ability to stop a long and heavy train.  For getting one moving was pretty easy.  Tracks were typically level.  And steel wheels on steel rails offered little resistance.  So once a train got moving it didn’t take much to keep it moving.  Especially when there was the slightest of inclines to roll down.

Getting a long and heavy train moving was no good unless you could stop it.  And stopping one was easier said than done.  As trains grew longer it proved impossible for the locomotive to stop it alone.  So each car in the consist (the rolling stock the locomotive pulls behind it) had a manual brake.  Operated by hand.  By brakemen.  Running along the tops of cars while the train was moving.  Turning wheels that applied the brakes on each car.  Not the safest of jobs.  One that couldn’t exist today.  Because of the number of brakemen that died on the job.  Due to the inherent danger of running along the top of a moving train.  Luckily, today, all brakemen have lost their jobs.  As we have safer ways to stop trains.

Of course, we don’t need to just stop trains.  A lot of the time we just need to slow them down a little.  Such as when approaching a curve.  Going through a reduced speed zone (bad track, wooden bridge, going through a city, etc.).  Or going down a slight incline.  In fact slowing down on an incline is crucial.  For if gravity is allowed to accelerate a train down an incline it can lead to a runaway.  That’s when a train gathers speed with no way of stopping it.  It can derail in a curve.  It can run into another train.  Or crash into a terminal building full of people.   All things that have happened.  The most recent disaster being the Montreal, Maine & Atlantic Railway disaster in Lac-Megantic, Quebec.  Where a parked oil train rolled away down an incline, derailed and exploded.  Killing some 38 people.  While many more are still missing and feared dead.

Dynamic Breaking can Slow a Train but to Stop a Train you need to Engage the Air Brakes

Trains basically have two braking systems today.  Air brakes.  And dynamic braking.  Dynamic braking involves changing the traction motors into generators.  The traction motors are underneath the locomotive.  The big diesel engine in the locomotive turns a generator making electric power.  This power creates powerful magnetic fields in the traction motors that rotate the axles.  The heavier the train the more power it takes to rotate these axles.  It takes a little skill to get a long and heavy train rolling.  Too much power and the steel wheels may slip on the steel rails.  Or the motors may require more power than the generator can provide.  As the torque required to move the train may be greater than traction motors can provide.  Thus ‘stalling’ the motor.  As it approaches stall torque it slows the rotation of the motor to zero while increasing the current from the generator to maximum.  As it struggles to rotate an axle it is not strong enough to rotate.  If this continues the maximum flow of current will cause excessive heat buildup in the motor windings.  Causing great damage.

Dynamic breaking reverses this process.  The traction motors become the generator.  Using the forward motion of the train to rotate the axles.  The electric power this produces feeds a resistive load that draws a heavy current form these traction motors.  Typically it’s the section of the locomotive directly behind the cab.  It draws more than the motors can provide.  Bringing them towards stall torque.  Thus slowing their rotation.  And slowing the train.  Converting the kinetic energy of the moving train into heat in the resistive load.  Which has a large cooling fan located above it to keep it from getting so hot that it starts melting.

Dynamic breaking can slow a train.  But it cannot stop it.  For as it slows the axles spin slower producing less electric power.  And as the electric current falls away it cannot ‘stall’ the generator (the traction motors operating as generators during dynamic braking).  Which is where the air brakes come in.  Which they can use in conjunction with dynamic braking on a steep incline.  To bring a train to a complete stop.  Or to a ‘quick’ stop (in a mile or so) in an emergency.  Either when the engineer activates the emergency brake.  Or something happens to break open the train line.  The air brake line that runs the length of the train.

When Parking a Train they Manually set the Hand Brakes BEFORE shutting down the Locomotive

The first air brake system used increasing air pressure to stop the train.  Think of the brake in a car.  When you press the brake pedal you force brake fluid to a cylinder at each wheel.  Forcing brake shoes or pads to come into contact with the rotating wheel.  The first train air brake worked similarly.  When the engineer wanted to stop the train he forced air to cylinders at each wheel.  Which moved linkages that forced brake shoes into contact with the rotating wheel.  It was a great improvement to having men run along the top of a moving train.  But it had one serious drawback.  If some cars separated from the train it would break open the train line.  So the air the engineer forced into it vented to the atmosphere without moving the brake linkages.  Which caused a runaway or two in its day.  George Westinghouse solved that problem.  By creating a failsafe railway air brake system.

The Westinghouse air brake system dates back to 1868.  And we still use his design today.  Which includes an air compressor at the engine.  Which provides air pressure to the train line.  Metal pipes below cars.  And rubber hoses between cars.  Running the full length of the train.  At each car is an air reservoir.  Or air tank.  And a triple valve.  Before a train moves it must charge the system (train line and reservoirs at each car) to, say, 90 pounds per square inch (PSI) of air pressure.  Once charged the train can move.  To apply the air brakes the engineer reduces the pressure by a few PSI in the train line.  The triple valve senses this and allows air to exit the air reservoir and enter the brake cylinder.  Pushing the linkages to bring the brake shoes into contact with the train wheels.  Providing a little resistance.  Slowing the train a little.  Once the pressure in the reservoir equals the pressure in the train line the triple valve stops the air from exiting the reservoir.  To slow the train more the engineer reduces the pressure by a few more PSI.  The triple valve senses this and lets more air out of the reservoir to again equalize the pressure in the reservoir and train line.  When the air leaves the reservoir it goes to the brake cylinder.  Moving the linkage more.  Increasing the pressure of the brake shoes on the wheels.  Further slowing the train.  The engineer continues this process until the train stops.  Or he is ready to increase speed (such as at the bottom of an incline).  To release the brakes the engineer increases the pressure in the train line.  Once the triple valve senses the pressure in the train line is greater than in the reservoir the air in the brake cylinders vents to the atmosphere.  Releasing the brakes.  While the train line brings the pressure in the reservoir back to 90 PSI.

This system is failsafe because the brakes apply with a loss of air pressure in the train line.  And if there is a rapid decline in air pressure the triple valve will sense that, too.  Say a coupler fails, separating two cars.  And the train line.  Causing the air pressure to fall from 90 PSI to zero very quickly.  When this happens the triple valve dumps the air in an emergency air reservoir along with the regular air reservoir into the brake cylinder.  Slamming the brake shoes onto the train wheels.  But as failsafe as the Westinghouse air brake system is it can still fail.  If an engineer applies the brakes and releases them a few times in a short period (something an experienced engineer wouldn’t do) the air pressure will slowly fall in both the train line and the reservoirs.  Because it takes time to recharge the air system (train line and reservoirs).  And if you don’t give it the time you will decrease your braking ability.  As there is less air in the reservoir available to go to the brake cylinder to move the linkages.  To the point the air pressure is so low that there isn’t enough pressure to push the brake shoes into the train wheels.  At this point you lose all braking.  With no ability to stop or slow the train.  Causing a runaway.

So, obviously, air pressure is key to a train’s air brake system.  Even if the train is just parked air will leak out of the train line.  If you’re standing near a locomotive (say at a passenger train station) and hear an air compressor start running it is most likely recharging the train line.  For it needs air pressure in the system to hold the brake shoes on the train wheels.  Which is why when they park a train they manually set the hand brakes (on a number of cars they determined will be sufficient to prevent the train from rolling) BEFORE shutting down the locomotive.  Once the ‘parking brake’ is set then and only then will they shut down the locomotive.  Letting the air bleed out of the air brake system.  Which appears to be what happened in Lac-Megantic, Quebec.  Preliminary reports suggest that the engineer may not have set enough hand brakes to prevent the train from rolling on the incline it was on when he parked the train for the night.  On a main line.  Because another train was on a siding.  And leaving the lead locomotive in a five locomotive lashup unmanned and running to maintain the air pressure.  Later that night there was a fire in that locomotive.  Before fighting that fire the fire department shut it down.  Which shut down the air compressor that was keeping the train line charged.  Later that night as the air pressure bled away the air brakes released and the hand brakes didn’t hold the train on the incline.  Resulting in the runaway (that may have reached a speed of 63 mph).  Derailment at a sharp curve.  And the explosion of some of its tank cars filled with crude oil.  Showing just how dangerous long, heavy trains can be when you can’t stop them.  Or keep them stopped.

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Outhouse, City Water, Sanitary Sewer System, Flush Toilet, Water Trap, Soil Stack, Sanitary Lift Stations, Weir Dam and Overflow Spillways

Posted by PITHOCRATES - April 11th, 2012

Technology 101

Before Indoor Plumbing People had to Walk some 50 Feet in Rain, Snow or Shine to go to the Bathroom

On the American sitcom The Beverly Hillbillies, Jed Clampett wasn’t sure if he should move his family to Beverly Hills after they found oil on his land.  He asks his cousin Pearl for advice.  She says, “Jed, how can you even ask? Look around you. You live eight miles from your nearest neighbor. You’re overrun with skunks, possums, coyotes, and bobcats. You use kerosene lamps for light.  You cook on a wood stove, summer and winter. You’re drinkin’ homemade moonshine, and washin’ with homemade lye soap. And your bathroom is fifty feet from the house. And you ask should you move!?”  Jed thinks about all of this and replies, “Yeah, I reckon you’re right. Man’d be a dang fool to leave all this.”  (This exchange begins at 11:40 on The Beverly Hillbillies (Season 1 – Ep. 1) The Clampetts Str).

On the American sitcom I Love Lucy, Tennessee Ernie Ford comes to visits the Ricardos in New York City.  On the day of his arrival, as he prepares to go to bed, he walks out of the apartment through the kitchen door with his suitcase.  Lucy and Ricky look at each other perplexed.  After a few minutes he comes back in and walks out of the apartment through the living room door.  After a few minutes he returns and approaches Ricky.  And whispers in his ear.  Exasperated, Ricky points and says, “Through the bedroom.”  In stunned disbelief Ernie says, “You mean it’s in the house?”  Ricky nods.  Ernie walks towards the bathroom and says, “Wait till I tell Mama about this.”  (See I Love Lucy Tennessee Ernie Visits).

Once upon a time, before indoor plumbing, people headed out of their house some 50 feet to go to the bathroom.  In rain, snow or shine.  To an outhouse.  Away from the main house.  Because of the stink.  And to keep their waste from seeping into the water table.  So their waste didn’t contaminate their drinking water.  So when they ever felt the call of nature they took that long walk.  Pushed open the door and squatted.  (Interesting fact: all outhouse doors open in for safety.  For if you were inside when a strong wind tipped the outhouse over you could open the door and then stand up, lifting the outhouse upright).  Or if it was a deluxe outhouse you may have sat down on some wooden planks.  Living like this was all well and fine when your nearest neighbor was 8 miles away.  Or in a suburban community with deep backyards.  For you could put your outhouse at the back fence.  Like your neighbor across the fence.  You can.  And some have.  But it’ll put a stink in the air.  And provide little privacy to do those most personal of things.  For when your neighbor sees the lady of the house walking back there it’s no secret what she’s going to do.

Flush Toilets are Possible thanks to City Water, Sanitary Sewer Systems, Water Traps and Stack Vents

Moving the bathroom into the house gave us true privacy.  So a lady could have a bowel movement without her neighbors knowing about it.  Two things made this possible.  City water.  And a sanitary sewer system.  These two things gave us the flush toilet.  A true marvel of engineering.  A porcelain bowl that holds a small amount of water.  Sitting on top of a pipe that ties into the sanitary sewer system.  A thing that makes the stink of an outhouse seem like a bouquet of roses.  Yet that stink doesn’t enter our homes.  Why?  Because of a simple thing called a water trap.  They come in a couple of shapes but typically have a u-shape somewhere in them.  Water enters and leaves at higher elevations.  Leaving the lower part always filled with water.  Providing a water seal between us and the stink of the sewer.  Thus preventing gases from entering our homes.  We build this trap right into our toilets.  On some models you can actually see the curly path the bowl drains into on the side of the toilet.

On top of the toilet base is a water tank.  With a valve and a float.  City water (under a slight pressure from the water plant) enters the tank through this valve.  When the tank is empty the valve is open and the water flows into the tank.  When the tank fills the float rises and closes the valve, shutting off the water flow.  At the bottom of the tank is a flapper valve.  When the tank is full of water the weight of the water presses down on this valve, sealing it shut.  When we flush the toilet we lift this flapper valve via a chain connected to a lever we operate with the flush handle on the toilet.  When we lift the valve the water in the tank can flow into the toilet bowl, washing the contents of the bowl into the pipe the toilet sits on.  As the water empties from the tank the flapper valve falls and seals the tank.  And with no water in the tank the float falls, opening the valve so water can refill the tank.

While the toilet tank fills because of the slight pressure they keep our city water under, the sanitary sewer system works under gravity alone.  All sewer lines in a building slope downward.  When they join other pipes they join in a ‘Y’ connection to make sure the new water entering another pipe enters flowing in the same direction of the water already in the pipe.  So as not to create any agitations or backpressure to the gravitational pull on the water.  To keep this water flowing in the downward direction.  If you have a basement in your house you can see a lot of this.  Downward sloping.  Y-fittings.  And you’ll also see one or two vertical pipes.  Soil stacks.  That other horizontal pipes run into.  Your sanitary waste (from floor drains, showers, sinks and toilets) flows to these soil stacks and down to a pipe under the floor that runs out to the sanitary line under the street.  If you follow these soil stacks up you’ll notice that they run all the way through the basement ceiling.  They in fact run all the way up and out through your roof.  Those little pipes you see protruding from your roof are stack vents.  These stack vents are critical in helping gravity work in your sanitary plumbing system.  By keeping a neutral pressure inside the pipes.  Making air pressure inside the pipes equal to the air pressure inside the house.  By equaling the air pressure on either side of the water traps the water stays in these traps.  If the system wasn’t vented the water wouldn’t stay in these traps.  As the column of falling water would compress the air below it creating a high pressure.  While creating a low pressure or vacuum above it.  Which would suck the water from the traps into the system above the falling water column.  And blow out the traps below the column.  Which would be rather nasty in the bathroom.  For it would blow raw sewage out of your toilet.  And onto you should you be in the bathroom at the time.

Sanitary Lift Stations have Backup Power and Failsafe Designs like Weir Dams and Overflow Spillways

At the beginning of all sanitary sew systems the pipes are their smallest.  Like inside a house where they connect to a floor drain, shower, sink or toilet.  As they join other pipes the pipe size increases.  To accommodate the increase in water volume.  The biggest pipe in a house is the one running to the sanitary line under the street in front of the house.  Which is a much bigger pipe as a sanitary line from each house connects to this line.  So it has to be big enough to handle all of the flow if everyone flushed their toilets at the same time.  Like at halftime during the Super Bowl.  And the pipes these ‘street mains’ connect to have to be even bigger.  For multiple ‘street mains’ connect to them.  And as more pipes join together they connect to even larger pipes.  And every one of these pipes is sloped downward to maintain the flow of water.  Pulled along by gravitational forces alone.  Which causes a problem.  Because continuously sloping bigger and bigger pipes downward will drive these pipes deeper and deeper underground.  Which can’t go on indefinitely.  As the ultimate destination is a wastewater treatment plant.  Which we typically don’t build underground.

So along the way we have to raise this wastewater so it can start its downward course again at a level closer to the surface.  We call these points sanitary lift stations.   Where a big pipe enters a wet well inside the station at a low elevation.  And exits the station at a higher elevation.  As water enters the wet well the water level slowly rises.  When the level reaches a certain elevation an automatic control system turns on pumps.  But not just any kind of pumps.  Some pumps with teeth.  That can grind up any solid waste that enters the sanitary sewer system.  From human waste.  To used condoms.  To feminine hygiene products.  And the myriad of other things that we shouldn’t flush down our toilets but do.  These pumps can pretty much grind up anything and spit it out into the discharge pipe of the station at a higher elevation.  So this wastewater can continue its journey to the wastewater treatment plant.

Some cities have a combined storm water and sanitary sewer system.  Which can tax the system during heavy rains.  For the water flowing into these wet wells will keep that level rising to a point the pumps may run continuously.  And should there be some damaging winds that take down the electrical grid these lift stations will throw-over to an emergency backup generator.  To keep those pumps running when we need them most.  To keep the water from rising too high in the wet well.  And the pipes feeding it.  For if those pipes fill up completely there will be no place for new water entering the sewer system to go.  Water will rise in manholes.  And out onto our streets.  Even out of our floor drains and into our houses.  As this would be a grave public health concern they often build failsafe protection in the sewer system.  The feed to the lift station will be a Y-connection.  Just past this will be a weir dam in the pipe.  A dam that blocks only the lower portion of the sewer pipe.  The pipe past this will run to some spillway into a river, lake or ocean.  If the flow in the pipe is too great for the lift station’s capacity it will spill over the weir dam and flow untreated directly into a larger body of water.  While this is bad it doesn’t happen often.  As it typically takes a ‘once in a hundred years’ rain to overtax a system.  And when it does there is so much storm water in the system that it greatly dilutes the harmful pathogens in the wastewater.

Our Sanitary Sewage Systems allow us to Draw Clean Drinking Water in the Same Room we Poop In 

Sanitary systems are gravity systems upstream.  As they get further downstream they get an assist from pumps.  As well as other powered valve and gates to redirect the water flow as necessary.  The bigger our cities get and the denser our city populations grow these active components become ever more critical to the gravity systems upstream.  So we provide backup power systems and failsafe designs.  We do everything possible to keep that wastewater flowing downstream and out of our homes.

Some of the greatest public health crises happen when these active systems break down.  For the power of gravity may influence our world a lot.  But the power of water is something to fear.  Especially when we lose control of it.  From tsunamis that overwhelm sewage systems in our coastal areas.  To 100-year rains that overwhelm our sewage systems in our interior areas.  To lift stations that fail and reverses the flow of wastewater in our sewage systems.  Worse yet is the discharge of raw sewage into our freshwater supplies.  That contaminate our fresh drinking water.  It doesn’t happen often but when it does it’s a health crisis of the first order.

But most times these systems work so well that we never think about them.  And can’t even imagine what life was like when you had to bundle up in the middle of winter and wade through thigh-deep snow to get to your bathroom.  Sitting on wooden planks in an unheated structure with the wind blowing through the slats.  Today we’re spoiled.  Not only do we not have to bundle up our bathrooms are heated.  And only a few steps away from us.  Because they are in the house.  Thanks to our sanitary sewage systems.  That can keep up with the waste production in our largest cities.  And allow us to draw clean drinking water in the same room we poop in.  If you really think about that it’s hard not to be as amazed as cousin Ernie was in I Love Lucy.

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