Valve Pit l Vacuum Mains l Vacuum Station
The valve pit package consists of the 3” AIRVAC vacuum valve, the valve pit cone, the sump, the pit bottom, the in-sump breather unit, and the air intake. The valve pit serves as the conduit through which sewage from homes enters the vacuum sewer system, flowing via gravity into the sealed sump that is part of the pit package.
Sewage level sensing is remarkably simple. As the sewage rises, air trapped inside the empty 2” (50 mm) diameter sensor pipe pushes in a diaphragm in the valve's controller/sensor unit, signaling the valve to open. When 10 gallons (38 liters) of sewage accumulates in the sump, the valve automatically opens. The differential air pressure propels the sewage at velocities of 15-18 ft/sec (4.5 to 5.5 m/s), disintegrating solids while being transported to the vacuum station. The valve stays open for four to six seconds during this cycle.
The valve pit provides the interface between the vacuum system and the house. It consists of two (2) separate chambers; an upper chamber that houses the vacuum valve and a bottom chamber that is the sump into which the building sewer is connected. These two chambers are sealed from each other. The AIRVAC valve pit can be installed in the street if desired, as it has an H-20 traffic load rating.
Each valve pit can accommodate sewage from up to four homes, although the most common configuration is one valve pit serving two adjacent houses. Houses connected to the vacuum sewers do not need any special plumbing fixtures.
Located above the sewage sump and surrounded by a fiberglass valve pit cone is a vacuum interface valve, which is pneumatically controlled and operated. Vacuum from the sewer line opens the valve and outside air from a breather pipe closes it. The interface valve is a full-port 3” (75 mm) valve and designed for handling 3” (75 mm) solids.
The valve pit cone houses the vacuum valve and controller. It is fabricated with filament-wound fiberglass and is suitable for H-20 traffic loading.
The sump portion of the valve pit is used to accept the wastes from the house. Elastomer connections are used for the entry of the building sewer. Holes for the building sewers are field cut by the contractor at the position directed by the engineer.
A pit bottom separates the upper and lower chambers of the valve pit. The pit bottom is bolted to the sump by stainless steel hardware and a sealing O-ring. This seal prevents water from entering the sump, thus eliminating any extraneous flows into the system
The AIRVAC controller requires a source of atmospheric air to the actuator chamber permitting spring assisted closing of the vacuum valve. Without this air, the valve will remain in the open position.
Early vacuum systems used an external breather for this source of air. This has been replaced by the in-sump breather, which uses atmospheric air from the sump. In the event of low vacuum conditions where the valve would not open, floats in the in-sump breather protect the controller from unwanted liquid.
Atmospheric air used for transport enters through the 4” (100 mm) screened air-intake on the homeowner’s gravity line. There are no odors at this air-inlet due to the small volumes of sewage and short detention time in the sump.