This command aids in the design of duplex sanitary or storm sewage lift stations. The program assumes a duplex station, with the second pump used solely for backup. That is, there are no provisions for multiple pump operation. The system head curve and pump curve are calculated using the least squares method of curve fitting through three points. To calculate the three points input the length of the force main (length of pressurized pipe), an assumed low-level wastewater surface elevation in the wet well, the elevation of the static lift in the force main, the sum of minor loss coefficients in the force main, and three flow rates that adequately cover the desired range of pump operation. The total dynamic head is calculated for each of the three flow rates by adding the static head, friction losses, velocity head, and minor losses that are calculated by the program from the input data. The next step is the calculation of the pump curve. The user should select one or more pumps from a manufacturer's catalog that will produce the desired operating conditions. The input data consists of the pump shutoff head (flow rate equal to zero), a head and flow rate near the desired operating point, and a head and flow rate beyond said operating point of the pump curve.
The system head curve and the pump curve are then
intersected to produce preliminary operating point results. If the
user is not happy with the results, click the Edit Input Values
button and change any of the parameters. When the user attains the
desired results then proceed with the wet well design by clicking
OK.Input for the wet well design includes type of wet well, wet
well dimensions, invert elevation of the lowest line entering the
wet well, and minimum wastewater depth in the wet well (usually
specified by the pump maker). The lead pump's wet well volume is
calculated using a formula from Metcalf & Eddy's Wastewater
Engineering: Collection and Pumping of Wastewater: V = CT/4,
where V equals required volume in gallons, C equals pump capacity
(GPM), and T equals minimum time in minutes of one pumping cycle.
After wet well design the program assigns a new low level
wastewater surface elevation in the wet well, and then recalculates
the system head curve and final operating point. At this point the
user may change any or all of the input parameters. If no changes
are needed then click OK to show the Final Results report.
