Why Does a Borehole Motor Strip Its Splines? Hidden Causes, Costly Risks & Proven Solutions
If a Borehole Motor Strip Its Splines, the motor may continue running while the pump stops delivering water. Although this type of failure is not common, it usually points to a problem between the motor and pump connection. Understanding the cause can help prevent costly repairs and repeated breakdowns.
What Are Splines in a Borehole Pump System?
Splines are the grooved connection between the motor shaft and the pump shaft. Their job is to transfer power from the motor to the pump. When the splines wear down or strip, the motor can still spin, but the pump may stop working properly.
What Does It Mean When a Borehole Motor Strip Its Splines?
When a Borehole Motor Strip Its Splines, the connection between the motor and pump becomes damaged. As a result, the motor can no longer transfer enough torque to the pump.
This can cause:
- Little or no water output
- Reduced pump performance
- Sudden system failure
- Unusual vibration or noise
Often, the motor still sounds like it is working. Therefore, the problem can be confusing without proper inspection and may appear similar to a pump running but no water* issue.
Common Causes of Spline Failure
Spline failure usually develops from stress, poor alignment, incorrect pump sizing, or harsh borehole conditions.
Misalignment Can Make a Borehole Motor Strip Its Splines
Poor alignment between the motor and pump is one of the most common causes of spline failure. When the two components are not aligned correctly, uneven pressure is placed on the spline connection. As a result, friction, wear, and stress increase over time. Eventually, the spline teeth begin to wear down until the motor and pump can no longer connect properly, causing the splines to strip
Excessive Torque Load
Every borehole pump has a designed operating range. However, blockages, high pressure demands, or incorrect system setup can force the pump to work harder than it should.
Blocked pipework, high head pressure, and poor pump selection* can all increase torque load. Consequently, the spline connection takes more strain and may fail sooner.
Pump Running Dry
A submersible pump depends on water for cooling and lubrication. Without enough water, heat and friction rise quickly, often leading to pump overheating* and accelerated component wear. According to Grundfos, dry-running protection# is one of the most important safeguards against pump damage.
Friction damages internal components, while heat adds more stress to the motor and shaft connection. Eventually, dry running can damage the splines, bearings, pump shaft, or even cause a borehole motor to burn out.
Worn or Low-Quality Components
Cheap couplings and poor-quality replacement parts often fail faster than reliable components. Older systems can also develop spline wear after years of service.
Neglected maintenance makes the problem worse because small wear points are not corrected early.
Sand and Abrasive Water
Many boreholes produce sandy or abrasive water. These particles act like grinding material inside the pump.
Over time, sandy or abrasive water can wear down important pump components and even lead to bearing failure*,
including damage to:
- Bearings
- Shafts
- Impellers
- Splines
- Couplings
Therefore, sand control is important when the borehole produces visible sediment.
Incorrect Pump Selection
An incorrectly sized pump places unnecessary strain on the system. An oversized pump may overload the motor, while an undersized pump may run outside its safe performance range.
Proper pump sizing should consider borehole depth, water demand, pressure requirements, and flow rate. Our borehole pump sizing calculator* can help you choose a suitable option.
Frequent Start and Stop Cycles
Frequent cycling creates repeated torque shocks. Each start places sudden load on the spline connection.
Too many start-stop cycles can weaken the mechanical connection and shorten the life of the pump and motor.
Signs of Stripped Splines
Several warning signs may point to spline failure:
- Motor running but no water delivery
- Weak or inconsistent water flow
- Sudden loss of pressure
- Unusual vibration or a pump vibrating excessively*
- Mechanical noise from the pump
- System worked before, then failed suddenly
Because these symptoms can also point to other borehole pump problems, proper diagnosis is important.
How to Prevent a Borehole Motor Strip Its Splines
Preventing spline failure is usually cheaper than repairing the damage.
Correct alignment should always be checked during installation. Proper alignment reduces friction and protects the motor shaft, pump shaft, and coupling.
Your pump should also match the borehole depth, flow requirements, and pressure demand. This prevents unnecessary torque load.
Sand protection may be needed if the borehole produces abrasive water. Filters, sand separators, or pumps designed for sandy conditions can reduce internal wear.
Stable water levels are also important. The pump must remain properly submerged to avoid dry running, overheating, and mechanical stress.
Pressure tanks and suitable control systems can reduce frequent cycling. As a result, the motor starts less often, and the spline connection lasts longer.
Quality components matter as well. Reliable motors, couplings, and pump parts usually cost more upfront, but they reduce repeat failures and downtime.
What to Do If Splines Are Already Stripped
Once splines are stripped, the repair depends on the level of damage.
Depending on the failure, the solution may include:
- Replacing the coupling
- Replacing the pump shaft
- Repairing damaged pump components
- Replacing the motor in severe cases
- Upgrading the full pump and motor setup
A technician should inspect the full system before replacing parts. Otherwise, the same failure may happen again and may eventually result in issues where the borehole pump starts then stops* unexpectedly.
When a System Upgrade May Be Necessary
Sometimes spline failure is a warning sign of a larger system problem.
Repeated failures may mean the pump is incorrectly sized, the borehole conditions have changed, or the system design is wrong.
Simply replacing damaged parts without correcting the root cause can lead to another costly breakdown.
Need Help Diagnosing Borehole Pump Spline Failure?
If a Borehole Motor Strip Its Splines, you need to find the real cause before replacing components.
At Pumps Africa, we can help you diagnose the issue, inspect your pump and motor setup, and recommend the correct repair or upgrade.
Our team can assist with borehole pump failures, motor problems, pressure issues, dry-running damage, and complete system assessments.
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