The working principle of vacuum toilets
Vacuum toilets are introduced within the concept of new sanitation to add some extra transportation power to the black water flow. Black water is conceived as a slurry that probably does not have enough viscosity to get transported over longer distances. Vacuum systems were readily available in naval and aviation applications. In the naval application the most important aspect is not the vacuum, but the toilet with a valve instead of a siphon. Obviously the slope of a discharge pipe in a ship is not always positive as a result of the swell of a ship. With a (temporarily) negative slope of the discharge pipe the valve prevents water flowing back into the bowl.
In aviation the application is logical for the same reason, with the advantages of the valve in the toilet bowl being evident during landing and take-off. Moreover in a plane vacuum is abundantly available. In a static application as a house hold, the remaining advantage is the theoretical extra level difference due to the negative pressure that may be applied in the pipe, which results in a larger available head loss for transport. In this short paper the hydraulic functioning of the vacuum systems will be demonstrated.