Working Principle and Characteristics of On-line Vacuum Toilets

Working Principle and Characteristics of On-line Vacuum Toilets

On-line vacuum toilet is the mainstream sanitation system widely adopted in high-speed trains, motor cars and modern mobile public toilets, which features instantaneous vacuum generation and atmospheric sewage tank operation. Different from the traditional vacuum holding type toilets that maintain continuous negative pressure in the sewage tank, the on-line vacuum structure only generates vacuum temporarily during the flushing process, realizing efficient and energy-saving sewage disposal.

Comparison: On-line Vacuum vs. Vacuum Holding Type

The core vacuum source of the on-line vacuum toilet is theventuri vacuum generator, which is mostly driven by the vehicle’s high-pressure compressed air system with a working pressure of 0.7 to 0.9 MPa. No vacuum or negative pressure is stored in the sewage tank at ordinary times, and the tank always keeps an atmospheric pressure state, which greatly reduces the structural and sealing requirements of the tank body.

The entire flushing and sewage suction process is completed in an instantaneous cycle. When the flush button is pressed, the control solenoid valve opens instantly, and high-pressure compressed air rushes through the nozzle of the venturi injector at a high speed. According to the venturi effect, the rapid airflow sharply reduces the local pressure, forming an instantaneous negative pressure (vacuum) in the small transfer cavity below the toilet bowl. This temporary vacuum quickly opens the toilet slide valve and sucks the dirt and sewage from the bowl into the transfer cavity.

After the sewage suction is finished, the system switches the air circuit immediately. The vacuum generator stops creating negative pressure and starts to deliver positive-pressure compressed air. The positive pressure pushes the dirt in the transfer cavity smoothly into the normal-pressure sewage tank. Once the whole flushing procedure is completed, the air supply stops, the temporary vacuum disappears instantly, and all pipeline structures return to the atmospheric standby state.

This working mode endows on-line vacuum toilets with prominent practical advantages. Firstly, the sewage tank does not bear negative pressure for a long time, which avoids vacuum leakage failure caused by aging of tank body and sealing parts, reducing maintenance difficulty and cost. Secondly, the vacuum generator only works during flushing instead of running intermittently for vacuum maintenance, effectively lowering overall energy consumption. In addition, the atmospheric sewage tank has a simple manufacturing process and higher safety, with no risk of sewage backflow caused by pressure loss.

Although the instantaneous vacuum supply will lead to a slight attenuation of suction force under high-frequency simultaneous use of multiple toilets, the optimized pipeline and jet design ensure stable and clean flushing effect in conventional scenarios. Thanks to its high efficiency, low failure rate and energy-saving performance, the on-line vacuum toilet has completely replaced the traditional vacuum holding type and become the standard configuration of modern rail transit and mobile vacuum toilet equipment.