Launder Design Program

This program is used to design the manifold that will be used for transporting water out of the sedimentation tank to the exit channel. The launder will be located between the top of the lamella and the surface of the water in the sedimentation tank. The orifices are on the top of the launder and arrayed to the side. The Launder program uses equations found in the fluids functions and sedimentation programs.

Launder Design Program Algorithm

Launder AutoCAD Drawing Program

Algorithm

Given the maximum flow rate through the treatment plant, and the number of sedimentation tanks in the plant, the flow rate for each sedimentation tank is equally divided between the number of sedimentation tanks. The length of the manifold section of the launder is the same as the length of the tank, minus the width of the exit and inlet channels and the thickness of the walls, minus the height of the cap fitting over the end of the launder. The cap height must be taken into account so there is enough room to remove the launder if necessary.

To determine the number of orifices in the launder, the length of the established manifold is divided by the specified orifice spacing (center to center), found in the Design Assumptions. Note that there are two rows of orifices on a single manifold. This number is rounded down to the nearest whole number.

The user determines the number of launder pipes per sedimentation tank (N.SedLaunders). From that number the flow rate through each orifice is calculated.

Using an iterative program found in the Fluids Functions (ND.Manifold) and the available pipe sizes, the nominal diameter of the manifold is determined and defined as ND.SedLaunderEst. This equation is a function of different parameters established in the Design Assumptions.
The total head loss in the launder is then calculated using the HL.Manifold equation found in the Fluids Functions. This equation is defined below with the given inputs and a minor head loss of 0.

Next, the head loss through the orifice is the given head loss, HL.SedLaunderBod, minus the calculated head loss through the whole launder. This is defined as HL.SedLaunderOrificeEst.
Finally, the diameter of the orifice holes is calculated using the D.Circle equation from the fluids functions. This number is rounded to the nearest available drill size. Written out, the equation is as follows:

Flow through the Launder

The launder fits into a coupling in the exit channel wall of the sedimentation tank. The length of the coupling is equal to the thickness of this wall. Control pieces that fit into this coupling have been designed to stop the flow between the sedimentation tank and the exit channel when it is necessary to drain the tank.

To stop the flow, a short stub of PVC pipe is attached to a PVC cap which fits into the end of the coupling on the exit channel side. The dimensions for this cap are derived from the PipeSizes matrix in the Pipe Database that defines the dimensions for a cap based on Nominal Pipe Size.
 
To re-fill the sedimentation tank with clean water from the exit channel, a uniquely designed control piece is fitted into the launder coupling. The launder is removed from its place when the tank is drained. Then, a control piece consisting of a short pipe covered by a cap with a single orifice is fitted in its place. The size of this orifice is calculated so that the flow rate of water into the empty sedimentation tank is not higher than the flow rate of water out of the other sedimentation tanks so that the plant water level height does not drop.

The height used in the equation is the difference in height of the water in the exit channel and the height of the center of the orifice, calculated as:

Once the tank is refilled, the control piece is removed and the launder replaced.