Pneumatic Evacuation to Prevent Freezing in Outdoor Sump Pump Drains

Sump pumps protect below-grade structures from water damage by pumping water from a sump well to the surface through vertical discharge pipes. However, after draining the sump well, the discharge pipes typically remain water-saturated, which is problematic whenever the discharge pipe is exposed to freezing conditions that cause damage from the expansion of freezing water. Current methods to protect discharge pipes from freezing include heat tape or routing the discharge pipe through a conditioned space. This study presents a theoretical analysis and hydraulic experiments for a new method using pneumatic evacuation immediately after each pump activation. The results demonstrate the feasibility of this new method for vertical pipe lengths up to 3.05 m (10 ft), pipe diameters up to 52.6 mm (nominally 2 in.), compressed air with a minimum pressure of 138 kPa (20 psi), and a minimum duration of 10 s.

Sump pumps are an important part of the system that keeps water from damaging basement walls and floors. Sump pumps are found in a sump well below the basement foundation. Water accumulates in the sump well and is pumped to the surface and away from the house through polyvinyl chloride (PVC) pipes. This vertical PVC pipe remains full of water from approximately the depth of the foundation to the ground surface. Often, the discharge pipe is exposed to freezing conditions and is subject to damage from the expansion of freezing water. The current methods employed to protect discharge pipes from freezing are using heat tape or routing the discharge pipe through conditioned space. At times, these methods are not possible or practical. In this study, an experiment was performed using varying pressures of compressed air at varying time durations to remove water from varying pipe diameters. The results of the experiment show that water can effectively be removed from a 2-in.-diameter 10-ft-long pipe using 20 psi compressed air for 10 s. Based on this study, the proposed method to use compressed air to remove water from below-grade sump pump discharge pipe subject to freezing is a reasonable alternative to the currently used methods.