# Handling storm drain failure

miamicanesOctober 7, 2006

How do sump pumps handle storm drain failure (something that seems to happen on a regular basis during summer afternoon rainstorms in Florida)? Do they have a sensor that detects the backup condition and automatically throws a valve to redirect the water pumped from under your house to somewhere else (like a pipe aimed at the street, or if that's illegal, redirects the water to your lawn sprinklers just to have somewhere to send it)? Or are the pumps powerful enough to overcome storm drain failure and force YOUR water into them anyway... even if it turns the storm drain at the curb in front of your house into a geyser because the water doesn't have anywhere else to go?

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lazypup

In the world of high tech control systems a sump pump is as dumb as a box of rocks. Sump pumps have only two functions, On or Off which is controlled by a float switch in the sump and the basic funtion is, if the foat is up the pump is on and when the float is down the pump is off.

Although there are some extremely rare and very expensive exceptions, as a rule a sump pump is a high volume/low pressure pump. Most sump pumps are rated for Maximum volume at not more than 12 feet of static head pressure and maximum operating pressure of not more than 20 feet of static head.

Static Head Pressure is then the result of adding "Vertical Head Pressure" and "line Friction loss" which is expressed in the equivalent feet of vertical head pressure, by example..let us assume a pump installation where the actual vertical lift is 8 feet. Now assume it is pumping into a long line that has 2' of vertical head friction loss. The resultant output pressure would then be 8' + 2' = 10' of vertical lift times the physical weight of water per foot (.434lbs/ft)= 10'x.434lbs/ft = 4.3psig.

Obviously 4.3psig would not be sufficient to operate a lawn irrigation system and code strictly prohibits discharging a sump pump into the house DWV system or onto a street, roadway or other public thoroughfare so the options are to discharge directly on the ground on your property or into an approved storm sewer or storm drainage ditch. If that said storm drain is already filled to capacity it cannot accept any additional load from your sump pump, and if your sump pump cannot discharge it simply cannot take in any more water so it sits there "Spinning its wheels" so to speak.

Typically a sump pump will have a 2" diameter discharge line and we typically install a 4" or 6" corrugated flex pipe storm drain line from the house to the municipal storm drain. The storm drain line is then terminated just slightly above grade at the structure end and the 2" line from the pump is discharged into the storm drain line but the point of connetion is left open in the same manner as a laundry standpipe line. In this fashion if the storm drain line backs up the excess water from the sump pump will spill out of the connection at ground level and will run onto the lawn.

October 7, 2006 at 8:05AM
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