Brief description

A tube in an inverted ‘U’ shape that causes a liquid to flow upward, above the surface of a reservoir, with no pump, but powered by the fall of the liquid as it flows down the tube under the pull of gravity, then discharging at a level lower than the surface of the reservoir from which it came.

Use / Function

• Primary use: Transferring liquids between containers without pumps.
• Secondary uses: Emptying tanks, aquariums, or flooded areas.
• Critical application: The S-trap in Toilets and sinks to block sewer gases.

Operating principle

It relies on gravity and cohesion/atmospheric pressure:

1. Priming: The tube must be filled with liquid initially.
2. Gravity Pull: The column of liquid in the longer (downward) leg is heavier than the column in the shorter (upward) leg.
3. Pressure Differential: Gravity pulls the liquid down the long leg, creating a partial vacuum at the top of the bend.
4. Flow: Atmospheric pressure pushes the liquid from the upper reservoir up the short leg to fill the vacuum, maintaining continuous flow until the levels equalize or the intake is exposed to air.

How to create it

Simple Transfer Siphon

1. Tube: Get a flexible hose or bent rigid pipe.
2. Position: Place the source container higher than the destination.
3. Prime: Submerge the entire tube to fill it with liquid, OR suck on the lower end (carefully!) until liquid flows over the arch.
4. Flow: Keep the outlet end lower than the source surface.

S-Trap (Plumbing Siphon)

1. Shape: Bend a pipe into an ‘S’ or ‘P’ shape horizontally/vertically.
2. Install: Place it under a drain (sink, toilet).
3. Function: It retains a small amount of water in the dip, sealing the pipe against gases from downstream while allowing wastewater to pass when pushed by new flow.

Materials needed

• Tube: Plastic hose (PVC, vinyl), Rubber tubing, Metal pipe (copper, lead), or bent Glass.
• Rigid Siphons: Ceramics or Metal for permanent fixtures.

Variants and improvements

• Self-Priming Siphon: Includes a bulb pump or shaker valve to start flow without suction.
• Bell Siphon: Used in aquaponics/flush tanks. A bell over a standpipe creates a siphon automatically when water level rises.
• Inverted Siphon: Used in Aqueducts to cross valleys. The pipe drops down and goes back up; pressure pushes water back to (almost) the same height.

Limits and risks

• Height Limit: Atmospheric pressure limits the maximum height (lift). For water at sea level, it’s theoretically ~10 meters, practically ~7 meters.
• Air Leaks: Any hole in the tube breaks the vacuum and stops the flow.
• Gas Accumulation: Dissolved gases can bubble out at the top of the arch, breaking the siphon.
• Contamination: Siphoning by mouth can lead to ingesting toxic liquids (gasoline, sewage).

Related inventions

• Toilet: Relies on a siphon for flushing and sealing.
• Aqueduct: Uses inverted siphons.
• Pipes: The material used.
• Pump: The active alternative.