How do municipal water systems work? How does a house on top of a hill have water pressure, but the house at the bottom of the valley isn’t overrun with sewage?
In: Engineering
Water pressure is created in the water pipes either with a water tower where gravity provides the pressure or pipes. There is a reason that the water tower is on tops of the hill so everything below it has water pressure. For high buildings like a skyscraper you can have a water tank in the tops of it you pump water to and then let it flow down to the rest of the building.
For sewage, you build the pipes so they always go downhill and if he end is a low point like a valley you have pumps that pump it away to the sewage treatment. The system with an inlet from the buildings is open and not pressurized like the freshwater system so it can’t flow uphill and back into a house. Pipes after pumps where you do not have any outer inlets are of course pressurized so it can move uphill.
To augment the other Redditor; drain pipes under ground are built with a “fall line.” The trench they dig to lay the pipe is always downhill because they make sure to dig it downhill away from the structure.
That is to say, grade (the height of the ground at the surface) may vary due to hills and valleys ect but the end of the floor of the trench they dig is always physically below where the pipe comes out of the building. If they come to a hill, they just move more dirt (dig “deeper.”) In certain conditions, this may make a sewage pump necessary at some point along the drain line if the place where the pipe comes out of the building is physically lower that the sewage treatment plant or wherever the drain empties. To limit this, city planners try to build the sewage treatment plant in the lowest possible spot. But then this means the plant may be subject to flooding during heavy rains and the treatment plant is typically near a river or body of water (because a natural body of water or river is typically the low point in an area.) Often they protect the plant with dikes and walls.
Most “fall lines” are between 1/4 of an inch and 3 inches per foot. So if you started at where your pipe comes out of the building and measured out 1 foot, at the one foot mark, the floor of the trench would be between 1/4 and 3 inches lower. This same slope would be maintained through the length of the pipe until it reached it’s destination or a sewage pump. [if the fall line is less that 1/4 inch the drain will clog too easily, if the fall line is greater that 3 inches, the water will flow too fast and leave solids behind.]
Remember, if you are 2 miles away from the building digging the trench; the trench floor would need to be on that slope as measured from the pipe’s origin, not the ground surface (grade) where you are 2 miles away. Grade can vary greatly two miles away.
Water pressure is supplied by use of water towers and/or large pumps in pumping stations. Sewage systems are built to create pressure pulling away from homes, feeding sewage downhill to lower points than homes, use of reservoirs to freely fill with overflow rather than have it fill up and back up into homes. May also be valves that can be closed off within the system.
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