In typical vacuum system layout, non return valve is connected to outlet pipe connected to discharge mechanism (position #1). In some situations where riser pipes are not connected to the horizontal main branch above its level, there is a possibility of back flow of black water to riser pipes. When toilet release button is pressed, because of water in BW pipes, vacuum system will become in operational and can overflow.
Solution is to relocate non return valve to a higher position above the water line, vacuum system will become operational and discharge process will occur. Instead of drilling a hole and welding a metal pipe to connect the non return valve, we have developed a rubber connection point. Rubber connection is inserted through drilled hole and on the other side non return valve is connected.