How Sovent® Single-Stack Sanitary Drainage Works

Sovent® single-stack sanitary drainage, waste & venting (DWV) systems transport sanitary wastes from plumbing fixtures to a legal point of disposal while protecting the trap-seal of each fixture. The Sovent® system prevents pressure excursions from exceeding +/- one inch of water column, which is the standard for sanitary drainage systems. A Sovent® system consists of a vertical stack open to the atmosphere (Fig. 1), horizontal branches to each fixture (Fig. 2), Sovent® Aerator fittings (Fig. 3), and Sovent® De-aerator fittings (Fig. 4).

A basic understanding of air and water movement in a sanitary system is required to illustrate how Sovent® accomplishes the DWV function in a single tube. Waste flow in a vertical stack will cling to the interior wall surface, proceed downward in a swirling motion, and leave an open airway in the center (Fig. 5). As the velocity increases, the falling waste encounters air resistance, which reduces the airway size (Fig. 6). As long as this airway exists, the pressures are balanced within the stack. Left uncontrolled, the flow velocity will increase to a point known as "terminal velocity" and may form a complete cross-sectional blockage of the tube (Fig. 7). This results in positive and negative pressures that may cause trap seal failures through induced siphonage and/or blowback. The Sovent® system design eliminates the formation of the "hydraulic plug" and maintains a core of air throughout the vertical stack (Fig. 8).

The horizontal branches transport waste from the fixture to the Sovent® stack. As waste flows along the bottom of the pipe, the air remains above. Sovent® branch sizing criteria allocates approximately 75% of the cross-sectional area for venting purposes (Fig. 9). Proper and sufficient slope on all horizontal components is required to ensure good system performance. Sovent® system branch run-outs provide design flexibility by offering developed length limitations that far exceed those of traditional DWV systems. At the fixture itself, the Sovent® system employs a proven sizing criteria designed to eliminate self-siphonage associated with traditional "s-trap" configurations. A typical Sovent® branch connection to a lavatory would consist of a 1-1/4" tailpiece, a 1-1/2" trap-arm, and a 2" vertical drop. The Sovent® system is gravity operated, which makes it impossible to completely fill a 1-1/2" trap-arm or 2" vertical drop from a 1-1/4" tailpiece (Fig. 10). With flow principles clearly defined, we can now examine how the remaining components work to ensure trap-seal protection.

The third component of a Sovent® system is the Aerator fitting (Fig. 11). Aerators are found at each typical floor of the Sovent® stack. Interior waterways and baffles are situated to control the effects of flow through the Aerator. Two distinct chambers are found in the body of the Aerator fitting. The first, called an offset chamber, is where flow from upper floors enters the fitting and actually offsets around the horizontal branch inlet (Fig. 12). This offset is designed to reduce the flow velocity and break up any partial hydraulic plug formation. After leaving the offset chamber, flow will again cling to the interior surface of the pipe and leave the center area open for air. This occurs at each Aerator fitting, resulting in fairly constant flow velocities throughout the vertical stack and eliminating the need for the "yoke-vents" found in traditional DWV systems. The second area, called a mixing chamber, prevents horizontal branch discharge from blocking the stack's cross-sectional area (Fig. 13). These two chambers are isolated from each other through the use of a separation baffle (Fig. 14). As horizontal flow enters the Aerator branch inlet, it must transition to a vertical flow before smoothly uniting with any stack flow. These actions take place on an intermittent basis since stack and branch flows may not be present simultaneously. An opening called a vent aperture is located above the separation baffle, which provides the venting action between the branches and stack (Fig. 15). A second baffle is located perpendicular to the separation baffle in the mixing chamber to prevent cross-flow from opposing branch inlets (Fig. 16). Aerator fittings have several inlet configurations available to suit a variety of project conditions.

The final component of the Sovent® system is the De-aerator fitting. De-aerators are found at the base of every stack and wherever the stack requires a horizontal offset (Fig. 17). The transition of vertical flow to horizontal flow can create excessive pressure fluctuations. This phenomenon is referred to as hydraulic jump, and its severity is related to flow volume and velocity. In some cases, a complete cross-sectional blockage of the horizontal pipe can occur (Fig. 18). The De-aerator fitting has two features designed to overcome this adverse effect. The first is an internal nosepiece, which reduces the flow velocity prior to the horizontal transition (Fig. 19). It also allows the air and waste to separate in the main chamber of the De-aerator. The second feature is the Pressure Relief Line or PRL (Fig. 20). The PRL allows for air movement in either direction resulting from stack flow pulling air downward or hydraulic jump pushing air forward. This maintains pressure excursions well within established limits. The PRL connects to the horizontal drain beyond the hydraulic jump zone, which extends ten stack diameters downstream of the vertical stack (Fig. 21). The Sovent® concept ends at the termination point of the PRL serving the lowest level De-aerator fitting. Fixture connections downstream of this point will require traditional venting methods.

In summary, the Sovent® system controls the hydraulic and pneumatic principles that occur within a sanitary drainage system by using specific geometric waterways found in the Aerator and De-aerator fittings. This eliminates the need for traditional venting requirements, thus conserving resources and labor while protecting the integrity of the trap-seal at each fixture. Contact our office for additional information.