Vacuum Sewer - Installation and Construction

Installation and Construction

The following section covers some basic information regarding the installation of vacuum sewer system. This section is not complete and should only give a basic overview.

Preferably HDPE pipes is used for vacuum sewer system pipe works, but PVC is also used in some countries. The recommended pipe classification is SDR11. Preferences should be given to electro fusion joints rather than butt welding. In general, butt welding shall only be allowed for pipe diameters of 150mm or more as the internal beads from butt welding methods will reduce the diameter especially for 90mm pipes significantly which can cause blockages inside the pipes.

It is most important not to use any 90° connection within the pipe work. This refers to any main or branch lines connections as well as to horizontal direction changes. Only wye-fittings and 45° bends may be used. Using 90° connection will lead to blockages within the system and may create a water hammer with temporarily pressure drops affecting the equipment.

It is furthermore very important to follow the pipe profiles which should be given by the system supplier. A minimum requirement is a constant slope of 0.2% within the so-called saw tooth profile. Upwards slopes and deviations from the given pipe profiles will lead to water sags causing temporarily blockages and pressure drops resp. additional head losses. In worst case, this can lead to a failure of the system. Especially the connection line from the collection pit to the next branch or main line needs to maintain a certain slope as otherwise water sags may cut off the valves from the vacuum inside the pipe system causing malfunction of the valves.

Special attention has to be given to the civil works related to the pipe work installation. Over-compaction or damages to the pipes by excavators may result in significant problems during operation. Even if the pipe withstands the pressure tests during construction and after backfilling, squeezed pipes or pipe full of concrete or other construction debris will lead to blockages and water sags during operation.

Although international guidelines give clear recommendations for gate valves (every 400-500m within main lines and for branch lines longer than 200-250m), all important side branches should be equipped with a gate valves. This will allow much faster pressure tests and leak detection during construction and will allow emergency measures if problems occur.

A monitoring system can be installed to indicate the status of the vacuum valves and collection chambers. The monitoring system indicates when problems are occurring so that preventative maintenance can be implemented before failure. Warning alarms are transmitted on valve pits that are developing problems, as well as valve pits that have totally failed and need immediate attention. Use of the monitoring system decreases the annual man hours needed to maintain vacuum sewer valve pits and makes the vacuum sewer system an even more affordable and reliable alternative sewer system.