The Vacuum Pump Station (VPS) houses a collection tank (to collect the sewage); discharge pumps to send the sewage to the treatment plant; controls to automate the station and vacuum pumps which create a negative pressure in the vacuum mains. (-0.5 -0.7 bar). Usually only one VPS is required in an average sized catchment. All electrical and mechanical equipment is housed in a dry environment and the operator is not in contact with any wastewater. All odours are minimized through the use of a bio filter.
Ideally a Vacuum Pump Station is located centrally within a catchment area but the designer can be flexible about this. A backup generator can be located at the VPS ensuring non stop operation in area’s where power is a problem or susceptible to Hurricanes or Cyclones.
When it becomes time to Upgrade any of your Vacuum Pump Station equipment then important considerations need to be made. Changes to pumps may affect temperatures in your station as well as controls. A change may also cover up any current system problems or be an opportunity to add to the catchment area. You should certainly Contact Flovac’s engineers or operators if you are considering this.
Although Mild Steel and Fiberglass Collection Tanks have been used in the past, most tanks are now made of Stainless Steel 316 due to the corrosive nature of the wastewater and the location of many vacuum systems near the ocean. Collection tanks can be either vertical or horizontal and have an operating volume as well as a buffer volume. All sewage from the vacuum network enters the collection tank which is under a negative pressure and is held here until the tank is 2/3rds full of liquid at which time the sewage pumps discharge the sewage to the Treatment Plant.
Non-clog centrifugal pumps are used with a through clearance of 90mm (3 inches). Horizontal pumps are more commonly used to allow for self priming without equalization lines. Importantly designers need to account for NPSH as you will be pumping against a negative pressure in the collection tank. If this is not accounted for correctly then cavitation will occur. VSD’s are often used to allow for staging of developments or variable conditions.
Typically Rotary Vane or Dry Claw Pumps are used but Liquid Ring pumps are also used. The operating level of the vacuum pumps is between -60 to-75 kPa (16-21 inches of Hg) this allows the pump operational times to be reduced in a well tuned system. We would typically expect the vacuum pumps to run approximately 4-6 hours per day and the monitoring of the air to liquid ratio is an important operational function. If you are thinking of upgrading your pumps read this first and contact us.
Although Flovac supplies monitoring systems for both the vacuum network and the vacuum pump station, many clients also require an integration with their own SCADA networks.
Odours rarely exist with vacuum sewerage systems as the sewage is never settled for enough time for septicity to occur. As a matter of course all air coming via the vacuum pumps tends to be treated by a bio filter in the form of a mulch bed. The sizing and maintenance of this is critical to ensure that back pressure does not impact on the system. Charcoal is rarely used successfully with vacuum sewage systems due to the warm moist air that comes from the system.
Vacuum Pump Station Buildings
Buildings can be designed to blend into the local area. The space required can be as small as a 10 foot container or as large as a normal house block. You need to ensure that there is room for truck access, a generator hard stand and odor control.