One of the most feared phrases in the water well industry is “It’s stuck”.
Every day hundreds, maybe thousands, of submersible motors are removed from wells without incident. However, every once in a while something causes one to hang up or keeps it from being removed.
Some of the common causes are shale or rocks that fall from above the pump and motor. These rocks wedge between the pump or motor and the well casing. They don’t have to be very big, just wedged in the wrong place. Sometimes carefully moving the motor up and down will free the unit. Another common reason for hang-ups is when a safety cable or the drop wire comes loose from the top and coils itself around everything down below. This can happen if the wire is not properly supported. Again moving the motor up and down carefully might free the unit.
One of the more uncommon reasons for a motor to remain stuck happened several years ago. An earthquake caused a horizontal shift in the earth’s crust. This shift was great enough to break the well casings and offset them by several inches. I don’t know how to get a motor out of this one.
From time to time, we also receive calls from contractors who have had to abandon 4” PVC cased wells due to the well casing forming around a 4” motor.
The contractor and his customer are frustrated because of the difficulty and expense associated with the process of restoring water service.
There is a misconception in our industry that the sole cause of the problem is the heat from the motor causing the PVC to shrink around the motor. Although the heat from the motor does weaken the PVC, it alone is not the root cause of the problem. CertainTeed, a leading manufacturer of PVC well casing located in Valley Forge, PA (610-341-7000), has spent considerable time addressing this problem. Through their laboratory and field work, they developed technical bulletins that deal with the subject in more depth.
Based on conversations with CertainTeed, a review of their bulletins, our lab testing, and phone conversations with contractors who have experienced the problem, we conclude that the solution to the problem is more dependent upon well construction than it is on the motor.
This infrequent problem seems to occur primarily in areas of loamy soil or when the drill cuttings are used as back fill. Saturated with water, this sludge becomes hydraulic fluid pressing on the PVC casing when the water level outside the casing is higher than the pump drawdown level.
Certain Teed determined the potential for PVC casing collapse can be eliminated by installing a firm and dimensionally stable backfill.
If the wells are properly backfilled, this pressure is distributed downward instead of inward.
Lab experiments show a 4” pump/motor running under shut-off or deadheaded conditions could soften the 4” well casing, but it would not cause the casing to melt, shrink or deform without external pressure. Even though the PVC will soften from the heat of the motor, particularly in the case of a locked pump or a “dead head” condition, it is the hydraulic pressure outside the PVC casing which causes it to form around the pump and motor.
Common Questions On This Subject:
Q “If Franklin Electric motors have built-in overload protection, why didn’t the overload trip?”
A Franklin Electric’s motors have built-in overloads in all 2-wire motors and our 1 Hp and smaller 3-wire motors. Internal overloads function on a combination of high amperage and temperature. In a deadheaded condition the amperage of the motor drops considerably. Since the overload looks for high amps it will not trip.
Q “I don’t have any gate valves or shutoffs in my plumbing. How can my system deadhead?”
A If the inlet to the pump would plug with debris or iron bacteria/algae, if a waterline between the pump/motor and tank would freeze, if something keeps a check valve from opening properly, all of these situations would cause the motor to run in a condition like deadhead.
Q “What if I use Franklin’s Pumptec, QD Pumptec or Pumptec Plus?”
A Franklin Electric’s Pumptec and QD Pumptec are No-Load or Out-of-Water sensors. Not all pumps react the same under deadhead conditions as they do in actual broken suction or out of water conditions. Deadheaded pumps can still load the motor sufficiently to satisfy the Pumptec and QD Pumptec, so they are not guaranteed to trip in this situation. Franklin Electric’s Pumptec Plus looks for a 25% change in the watt draw of the motor starting from its callibration point. This calibration point is set by the installer based on actual running loads and there may not be enough change during deadhead.
Q “If I abandon a motor in the well is there a potential for contamination?”
A Wells that are no longer productive should be properly filled and sealed to protect our ground water resource. As far as the motor, Franklin Electric’s submersible motors, used in water well installations, are filled with a non-toxic water based mixture. Material Safety Data Sheets (MSDS) are available upon request.