Figure 16. Water level controls used in dosing tank.
Figure 16. Water level controls used in dosing tank.
Float switches, as described in this bulletin, are a good choice for household systems where water is used nearly every day throughout the day. They are easy to install and inspect.
Electronic control panels are now available with timers to equalize flow to the mound throughout the day. Timers are a good choice for commercial systems that experience days with high flows over a few hours combined with days with extremely low flows. Dose tank sizing must be adjusted to store the high flows to be dosed to the mound over an extended period.
Simple float switches can signal the pump and alarm controls. The on switch is needed to turn the pump on and a second switch is placed below it to turn the pump off (Figure 16). The distance between the pump on and pump off switches yields the dose volume. The distance needed between the two switches depends on the size and shape of the dose tank. Sometimes a combination switch is used where the swing of the switch dictates the on and off level.
The gallons per inch in a circular tank (Figure 14(a)) can be determined by:
(pi/4)*(Diameter (inches))2 × (1 gal / 231 in3) = (Diameter (inches) × Diameter (inches)) / 294 = gal per inch of depth
The gallons per inch a rectangular tank (Figure 14 (b)) can be determined by:
Width (inches) × Length (inches) × 1 gal = gal per inch of depth 231 in3
Design Example
The gallons per inch in a 72-inch diameter circular tank
= (72 inches × 72 inches) / 294 = 17.7 gal/inch
(dose volume / gal per inch) = switch separation
(135 gal / 17.7 gal/inch) = 8 inches
Selected Parameter
(29) Tank shape: Circular
(30) Tank diameter: 72 inch
(31) Switch separation: 8 inch
All wastewater distribution systems that utilize a pump require electrical power and control systems. Proper wiring materials and installation procedures are critical to the safety of the installer, sewage system user and all individuals involved in future repairs and maintenance. Adequate wiring ensures reliable pump and system performance. Follow a few basic guidelines to ensure safe and reliable operation at a reasonable cost. In all cases, installation procedures must follow the specifications of the National Electric Code or any other prevailing code. Contact local electrical inspection authorities for permits and inspection requirements. Work should be done by a qualified electrical installer.