When flexible polyethylene (poly-pipe) kinks inside a well casing, water flow drops suddenly or stops entirely while the pump motor continues to run. Poly-pipe is favored for its corrosion resistance and ease of installation, but its flexibility makes it vulnerable to twisting, hydraulic shock, and thermal expansion downhole. A kinked drop pipe restricts or pinches shut the discharge line, traps the pump assembly in the casing, and can burn out the motor if left unaddressed.
Quick Answer
Poly-pipe kinks inside a well casing when motor startup torque twists the unanchored pipe, or when hydraulic water hammer stretches and drops the line. Using pipe with an insufficient pressure rating (under 160–200 PSI), omitting a torque arrestor, or failing to space pipe guides evenly allows the line to buckle under its own weight.
System Snapshot
- Affected Component: Polyethylene drop pipe, torque arrestors, well check valves.
- Severity: Critical. A kink can collapse completely, trapping the pump and motor downhole.
- Immediate Check: Check pump amp draw and flow rate. A sudden drop in gallons per minute with normal motor current points to a pinched or kinked line.
- Safe to Run: No. Pumping against a completely kinked pipe causes deadhead pressure, destroying impellers and overheating the motor.
What This Usually Means
Every time a deep well submersible pump starts, the electric motor produces an immediate rotational kick in the opposite direction of the impeller rotation (counter-torque). If the poly-pipe hanging in the well is unsupported, this torque twists the flexible pipe like a wrung towel.
Over dozens of start cycles, this twisting winds the drop pipe until it buckles, flattening into a sharp kink. The problem is accelerated when water weight inside the pipe pulls down on the stretched plastic while pressure cycles flex the pipe walls outward and inward. For detailed motor startup diagnostics, see Diagnostic: The Pump Runs but Only Produces a Trickle.
What Can Cause It
1. Absence or Failure of a Torque Arrestor
A torque arrestor is a split rubber sleeve clamped to the drop pipe just above the pump that expands to grip the casing wall. Without a functioning torque arrestor, 100% of motor startup energy is absorbed directly by the poly-pipe. Over time, the lower 10 to 20 feet of pipe corkscrews and collapses. See Troubleshooting Torque Arrestors on Deep Well Drop Pipes.
2. Using Under-Rated or Thin-Wall Poly-Pipe
Utility-grade poly-pipe rated at 100 or 125 PSI is not strong enough to serve as drop pipe in deep wells. The hydrostatic head (the weight of the water column) combined with pump operating pressure exceeds the tensile strength of thin plastic, especially in warm water conditions. Professional installations require high-density SIDR-7 or SIDR-9 poly-pipe rated for at least 160 to 200 PSI.
3. Hydraulic Shock (Check Valve Slam)
If the well’s check valves are spaced improperly or failing, water in the upper column crashes back down against the pump discharge when the motor stops. This downward hydraulic hammer stretches the poly-pipe vertically. When the pump starts again, the sudden upward surge compresses the stretched, flexible pipe, causing it to buckle laterally against the casing wall. Review Troubleshooting the “Check Valve Slam” in Vertical Risers.
4. Improper Suspension and Lack of Pipe Centralizers
Allowing excess slack during pipe installation creates resting bows or loops against the casing wall. As the pipe heats, cools, and bears the weight of the water, these bows bend past their minimum bend radius and turn into permanent kinks.
What Makes It Worse
- Deep Well Settings (>150 Feet): The weight of the water column increases downward tension, making warm poly-pipe much more prone to necking and kink-collapse.
- Frequent Motor Cycling: Rapid on/off cycles multiply the counter-torque forces applied to the pipe.
- Oversized Well Casing: A 4-inch pump inside an 8-inch casing has excessive room to rotate and twist before contacting the casing wall, dramatically worsening the kink angle compared to a 6-inch casing.
Testing & Diagnosis
| Check Step | Observation | Diagnostic Result |
|---|---|---|
| Flow vs. Amp Draw | Motor draws normal/high amps; surface discharge flow drops by 75% or more. | Pipe is pinched, restricted, or kinked downhole rather than disconnected. |
| Visual Pipe Inspection (Pull Test) | Pulling the drop pipe reveals an oval, flattened section or a spiral twist in the lower runs. | Rotational failure caused by torque or pipe wall failure under high tension. |
| Check Valve Verification | Pressure gauge drops to zero immediately upon pump shutoff. | Failed check valve causing vertical hydraulic shock cycles. |
| Casing Clearance Check | Pump hangs loose without a snug rubber guide contacting the casing walls. | Missing, undersized, or worn torque arrestor allowing unrestrained rotation. |
What to Do Now
- Kill Power to the Pump: Do not allow the pump to continue operating against a kinked line. Deadheading will melt the pump’s internal diffusers and ruin the motor windings.
- Prepare for Safe Extraction: Extracting a kinked poly-pipe well requires extreme care. A kinked section can jam against casing joints or the pitless adapter receiver. Review Recovering a “Dropped” Submersible Pump: The Recovery Checklist before rigging pulling equipment.
- Inspect the Extracted Pipe: Cut out and discard any section of poly-pipe that displays flattening, stress whitening, stretching, or ovaling. Polyethylene has a memory; once creased or kinked, it will always fail at that exact point under pressure.
Repair & Prevention Standards
When replacing poly-pipe in a deep well, adhere strictly to these installation practices:
- Upgrade the Pipe Spec: Install only NSF-certified 160 PSI or 200 PSI SIDR (Standard Inside Dimension Ratio) high-density polyethylene well drop pipe. Never use thin-walled schedule utility tubing.
- Install a Heavy-Duty Torque Arrestor: Secure a two-piece expandable rubber torque arrestor 1 to 2 feet above the pump discharge check valve. Adjust it until it clears the inside casing diameter with just 1/4 to 1/2 inch of total play.
- Install Cable Guards / Pipe Guides Every 20 Feet: Secure the submersible electrical wire and pipe using dedicated plastic snap-on guides or heavy-duty vinyl pipe tape. This centers the pipe in the casing and prevents lateral bowing.
- Use Stainless Steel Insert Fittings: Always use extra-long barbed stainless steel insert fittings secured with two opposing all-stainless hose clamps per joint. Heat the poly-pipe evenly with warm water (not an open flame torch) to seat the barb without weakening the plastic.
Closing
A kinked poly-pipe is almost always caused by mechanical twist or hydraulic shock, not random pipe failure. When pulling your well to fix a flow drop, never reinstall a creased line. Upgrade to 160+ PSI rated pipe, secure the motor with a properly fitted torque arrestor, and stabilize the drop line to keep it straight and functional inside the casing.