The variable aperture choke drain releases water at a predetermined rate. When the retention system exceeds the maximum storage capability, the emergency overflow pipe allows water to bypass the choke drain, allowing maximum flow.

Graf Choke Drain Shaft Overview

Variable installation depth from 22.5" – 41.3"using telescopic dome shaft Plastic cover can be walked on or cast iron cover can be driven on by a car* Boltable childproof cover Watertight to surface level No height offset between inlet and outlet 3,750 Sq. ft. maximum paved surface area handling Standard 4" connections Drain quantity adjustable from 0.132 to 1.72 gallons per second (see table below) * Vehicle loading capability with cast-iron lid is available for $139.00

Typical infiltration application:

Swale ditch stormwater solutions:

Using Graf percolation filtration systems, infiltration through swale-ditches can be accomplished regardless of soil conditions. Depending on the soil’s infiltration/adsorption performance (K_f), stormwater control can be achieved through a balance of infiltration and retention.

For delayed outflow into the drainage system, the Graf Choke Drain Shaft is the ideal solution. By adjusting the variable choke drain aperture, stormwater flow to the drainage field can be precisely controlled while providing a parallel path for emergency overflow.

A secondary benefit of swale-ditch infiltration is the cleaning effect the soil layer provides for the rainwater. This characteristic makes it particularly suitable for larger projects having higher levels of pollution in the surface water as occurs frequently in industrial applications.

Flow Rates:

Choke Drain Plate Details:

Choke Drain Shaft Dimensions:

Additional Resources:

Click here for USDA Natural Resources Conservation Service Michigan Guidelines for K_f Values.

Click here for USDA Major Land Resource Area (MLRA) Soil Survey Regional Offices