Vacuum Toilet

Posted by PITHOCRATES - April 24th, 2013

Technology 101

The Siphon in a Flush Toilet sucks the Waste out of the Toilet Bowl

The common flush toilet in our homes is located in a bathroom.  A dedicated room in our houses.  Often times tucked away off of a bedroom.  Private and secure.  Where we can take care of any of our business with comfort and dignity.  It’s nice.  Hiding that part of our life away from the rest of the world.  In fact, some people are such nervous pooers that they can’t go anywhere but at home.  Lucky for them they didn’t live in ancient Rome where communal toilets were long benches with holes in them.  And people sat next to each other while doing their business.  Elbow to elbow.  Literally.

What makes the flush toilet in our homes possible is basically one thing.  They don’t move.  They’re permanent installations that sit on terra firma.  And because of that they can use gravity.  When we flush a toilet water pours down from a tank into a bowl.  Forcing the contents of the bowl up and over the drain out of the bowl.  The siphon.  Filling this pipe completely with water.  So that when the water falls down into the sanitary sewer pipe it creates a siphon.  Pulling everything behind it down into the sanitary drain.  Where gravity pulls it down to pipes under our houses and into the sanitary sewer system under the street in front of our house.  Where these pipes slope downhill towards the wastewater treatment plant.

The flush toilet works in our house because they don’t move.  And we can dig pipes deep underground.  Two things we can’t do on boats, trains and planes.  So early boats and trains had a simple toilet.  If you looked down into the toilet seat on a boat you saw the water.  And if you looked down into the toilet seat on a train you saw the railroad track underneath.  Which could really chill a pair of butt cheeks on a crisp winter day.  Making a cold toilet seat in your bathroom in the morning seem toasty warm by comparison.  Early planes had a chemical toilet.  Basically a port-a-potty.  Filling the air with the aroma of a construction site toilet.

The Suction of a Vacuum Toilet is greater than the Siphon of a Flush Toilet

Today in most countries you can’t defecate into a river, lake or ocean.  Or onto railroad tracks.  It’s not sanitary.  And just plain disgusting.  But because boats, trains and planes move a flush toilet with a bowl full of water just isn’t an option.  Because water in a moving bowl tends to splash out of the bowl.  Which can splash corrosive waste in nooks and crannies around the toilet.  Making a mess in the lavatory.  Though chemical toilets were an option and we used them for some time they just didn’t smell good.  Especially on an airplane.  As you just couldn’t roll the window down for some fresh air.

A flush toilet on an airplane has another problem.  Water has mass.  To carry water for flush toilets increases the weight of the airplane.  Requiring more fuel.  As fuel is the greatest cost of flying airlines and aircraft manufacturers do everything within their power to reduce the weight of an airplane.  Which is why today’s aircraft use a vacuum toilet system.  Where instead of using water and gravity to create a siphon they use a vacuum pump to create a suction.  A vacuum toilet does not use water.  There is no water in the bowl.  When you ‘flush’ a drain opens in the bottom of the bowl and a powerful vacuum sucks it clean.

The suction of a vacuum toilet is greater than the siphon of a flush toilet.  Allowing smaller pipes as the powerful suction does not allow any clogging of pipes.  Smaller pipes (and no water like in a flush toilet) reduce weight.  Helping to cut the cost of flying.  That powerful suction also sucks out all of the stink with each flush.  Another benefit of the vacuum toilet.  Which is a good thing in a small room without a window you can open.

A Truck transfers the Sanitary Waste from an Aircraft Holding Tank into the Sanitary Sewer System

Planes pitch up, pitch down and bank left and right.  Which would be a problem for wastewater moving under the force of gravity.  Or for water in a bowl.  Which is another benefit of a vacuum toilet system.  Which doesn’t use gravity.  Or water.  So the pipes of a vacuum toilet system can run in any direction.  Up, down or flat and level.  The force of the suction will pull the waste to the holding tank no matter the path it takes to the holding tank.

As the flight progresses people use the toilets.  And the holding tanks fill up with waste.  When they land they are pretty full.  And the airlines need to empty them.  If you ever watched an airplane at a gate after it lands you will see a whirlwind of activity.  Baggage and freight comes off.  Then they load baggage and freight for the next flight.  Cleaning crews enter the aircraft.  Food service cleans out the galleys and loads food and beverages for the next flight.  Fuel trucks refuel the aircraft (either from a fuel truck or a fuel hydrant system in the apron).  And then there’s the poop truck.  Which will open a hatch on the belly of the aircraft.  Connect a large hose.  Open a valve.  And drain the holding tank into the truck.  Pump in some blue disinfectant.  And make the toilets ready for the next flight.

The poop truck then drives someplace where they can dump their load.  Larger airports may have a special building for this.  Where they drive in and stop over a grate in the floor.  Dump their load onto the grate.  Water sprays onto the floor to help wash everything into and through the grate.  Where it falls into a ‘chopper’ pump to break down the solids more.  And then it enters the sanitary sewer system at the airport.  Where it uses gravity to flow downhill towards a wastewater treatment plant.  Just like it does when we use the bathroom in the privacy and security of our home.

www.PITHOCRATES.com

Share

Tags: , , , , , , , , , , , , , , ,