A deep well submersible pump must remain adequately submerged and supplied with enough water throughout operation.
If the well cannot replenish water as quickly as the pump removes it, the dynamic water level may continue falling. Once the water reaches the pump intake, the unit can begin drawing air, producing unstable flow or operating without sufficient water.
This condition is commonly called dry running.
Dry running can damage the pump, motor, bearings and other components. It may also produce severe vibration, overheating, loss of discharge pressure and repeated control-panel trips.
Reliable protection requires more than installing a single sensor. The system should combine:
Confirmed well yield
Correct pump capacity
Suitable installation depth
Adequate submergence
Water-level or electrical protection
Safe shutdown logic
Controlled automatic restart
Commissioning and periodic testing
Dry-running protection is a backup system. It does not make an oversized pump suitable for a low-yield well.
Dry running occurs when a pump operates without enough water passing through its hydraulic section and around the motor.
The condition does not always mean that the entire well is empty.
A borehole pump may experience dry-running conditions when:
The dynamic water level falls below the pump intake.
Water intermittently covers and exposes the intake.
The pump produces more water than the well can supply.
A level sensor is positioned incorrectly.
An inlet screen becomes blocked.
Air or gas enters the pump.
A valve is closed or a pipeline is obstructed.
The pump loses flow because of mechanical damage.
A tank pump creates a vortex and draws air.
A well requires more recovery time between operating cycles.
Partial loss of submergence can be damaging even before the pump becomes completely dry.
The intake may alternate between water and air, causing unstable pressure, vibration and rapid changes in motor load.
Water performs several functions while the pump is operating.
It is the pumped medium, but it can also contribute to:
Motor cooling
Bearing lubrication
Hydraulic stability
Heat removal from internal pump components
Stable thrust conditions
Cooling of mechanical seals in applicable designs
When water flow is lost, these functions are reduced or disappear.
Possible consequences include:
A submersible motor normally transfers heat to the surrounding moving water.
If the water level falls too far, the motor may lose its cooling environment. Even when the motor remains partly submerged, insufficient movement along its surface can allow temperature to rise.
Many borehole pump bearings and bushings depend on water for lubrication and cooling.
Operation with air, insufficient water or a mixture of air and water can increase friction and wear.
Some submersible pump designs use mechanical seals that depend on the surrounding liquid for cooling.
Running dry can overheat and damage the sealing faces.
A multistage borehole pump is designed to operate with water moving through its impellers and diffusers.
Loss of flow can change the internal pressure distribution and thrust conditions. Repeated dry-running cycles can shorten the service life of thrust bearings and hydraulic components.
Air entering the intake can create unstable hydraulic forces.
The pump may produce fluctuating flow, noise and vibration, potentially damaging:
Pump bearings
Motor bearings
Couplings
Rising-main connections
Electrical cable supports
Check valves
When the pump begins drawing air, discharge flow and pressure may fall.
The control system may respond by repeatedly starting the pump or increasing VFD speed, making the condition worse unless dry-running logic is included.
A pump can be capable of delivering more water than the well can sustainably produce.
For example, a pump may initially deliver the required flow while drawing water stored inside the casing. If aquifer inflow cannot maintain that rate, the water level will continue falling.
The pump may then reach the dry-running protection level even though its hydraulic performance is normal.
This is primarily a well-yield and pump-selection problem.
Static water level is measured while the well is resting.
After the pump starts, the water level normally falls to a dynamic or pumping level. The difference is the well drawdown.
Installing the pump according to static water level alone can leave insufficient submergence during operation.
Use the stabilized dynamic water level at the required pumping rate when reviewing installation depth and dry-running risk.
A water level measured during a wet season may not represent the lowest level expected during dry weather.
Groundwater conditions can also change because of:
Drought
Irrigation demand
Nearby pumping
Changes in recharge
New wells in the same aquifer
Long-term groundwater decline
Dry-running protection should account for the lowest credible operating level, not only the level observed on the installation date.
Sediment, mineral deposits, biological growth or debris can restrict water movement through the well screen or pump intake.
The well may contain water, but the pump may not receive enough flow.
A restriction can also change motor current and discharge pressure, causing symptoms similar to a falling water level.
A pump installed too shallow may become exposed when the dynamic water level falls.
Installing it deeper may increase the available submergence, but excessive depth creates other risks, including:
Reduced distance from the well bottom
Greater exposure to sand and sediment
Higher rising-main and cable cost
Greater suspended load
Higher pressure at lower pipe sections
More difficult retrieval
Possible installation below the productive screen
Inadequate motor cooling when inflow occurs from above
Installation depth must balance water coverage, well geometry, screen position, cooling and bottom clearance.
A pump installed in a tank, reservoir or open body of water may draw air through a surface vortex even when the intake remains below the normal water level.
Vortex formation depends on factors such as:
Submergence above the intake
Pump flow
Tank geometry
Distance from walls and floor
Intake orientation
Water-entry direction
Nearby pumps
Turbulence
A level sensor alone may not detect this condition because the tank still contains water.
Some wells contain dissolved or free gas.
Gas entering the pump can reduce hydraulic performance and cause fluctuating current, pressure and flow. The symptoms may resemble partial dry running.
The water source should be evaluated if air or gas continues to appear even when the measured water level remains above the pump.
Dry-running protection should begin with reliable well data.
A pumping test can establish:
Static water level
Dynamic water level at a stated flow
Drawdown
Recovery after shutdown
Whether the water level stabilizes
Approximate well capacity under the test conditions
Changes in water quality or sand content during pumping
The dynamic water level must always be recorded together with the pumping rate and elapsed time.
A statement such as “the water level is 50 metres" is incomplete unless it identifies whether the measurement is static or dynamic and how much water was being pumped.
If the water level continues falling throughout the test, the proposed operating flow may not be sustainable.
Dry-running controls can stop the pump, but they cannot increase the well’s water supply.
The selected duty flow should remain within the well’s verified operating capability.
Avoid selecting a pump only because it can deliver a higher maximum flow. An oversized pump may:
Lower the dynamic water level rapidly
Cause frequent dry-run trips
Increase sand movement
Create unstable cycling
Operate away from its efficient range
Require throttling
Increase starting and electrical stress
If demand is temporarily higher than the sustainable well flow, a storage tank may provide a better system arrangement.
The well pump can fill the tank at a controlled rate, while a separate booster pump supplies the variable or peak demand.
The pump must remain below the lowest expected dynamic water level by the minimum submergence specified for the selected model.
The required depth should be checked against:
Stabilized dynamic water level
Seasonal decline
Drawdown during peak demand
Nearby well interference
Pump intake position
Complete pump and motor length
Well screen or perforation position
Water inflow direction
Motor cooling requirements
Distance from the well bottom
Sand and sediment conditions
Do not confuse pump setting depth with pump head.
Installing the pump deeper does not directly increase the vertical lift from the pumping water level to the discharge point. It mainly changes the pump’s position within the well and the available submergence.
The referenced SLAPK QJ installation instructions state that the first-stage impeller should be at least 2 metres below the dynamic water level and that the motor bottom should remain at least 3 metres above the well bottom. They also provide a model-specific limit for immersion below static water level.
These values are product instructions for the referenced QJ configuration, not universal limits for every borehole pump. Confirm the exact requirements for the ordered pump and motor.
Conductive level electrodes are commonly used in water wells.
A typical arrangement can include:
A low-level stop electrode
A higher restart electrode
A common reference electrode where required
A level relay in the control panel
When the water falls to the stop level, the control system opens the motor circuit and stops the pump.
The pump should not restart as soon as water touches the same electrode again. A separate restart level or time delay provides hysteresis and allows the well to recover.
Electrode suitability depends on water conductivity. Very low-conductivity water, scale or deposits can reduce reliability.
The supplier should confirm:
Electrode material
Cable type
Control voltage
Water-conductivity range
Maximum cable length
Installation depth
Spacing between electrodes
Resistance to corrosion and deposits
Float switches are widely used in tanks, sumps and reservoirs.
They can provide a direct low-level signal, but they are often impractical in narrow boreholes because they require space to move freely.
A float may become obstructed by:
The rising main
Power cable
Cable clamps
Well casing
Other sensors
Turbulence
Sediment
Use a float only where the installation provides adequate clearance and the device is approved for the liquid and depth.
A submersible pressure transducer can measure the water column above the sensor.
It may provide continuous level information rather than a simple wet-or-dry signal.
Advantages can include:
Adjustable stop and restart levels
Continuous trend monitoring
Remote telemetry
Seasonal water-level records
Alarm functions
Pumping-test data
However, the indicated level can be affected by:
Sensor elevation
Water density
Atmospheric-pressure compensation
Cable vent condition
Temperature
Calibration drift
Electrical noise
Incorrect reference datum
The transducer should be installed at a known elevation and protected from direct mechanical damage.
A submersible motor normally draws less power when the pump loses hydraulic load.
An electronic motor-protection relay may detect dry running by monitoring:
Current
Active power
Power factor
Motor load
A calculated combination of electrical values
This method can be useful because it does not require a separate downhole water-level cable.
However, low current does not uniquely prove dry running.
Similar readings can result from:
Closed or restricted intake
Broken pump shaft
Worn impellers
Gas entering the pump
Incorrect voltage
Incorrect VFD frequency
Motor or cable faults
Pump operation at an unusual point on its curve
The protection threshold should therefore be commissioned using measured data from the actual pump under normal operating conditions.
Do not copy a current setting from a different motor or pump.
A flow switch or flowmeter can detect loss of water delivery.
This is useful where dry running produces a clear reduction in discharge flow.
The logic should allow for the short period between motor starting and stable flow reaching the sensor. Without a suitable startup delay, the system may trip every time the pump starts.
Flow monitoring can also detect problems that a water-level sensor may miss, including:
Blocked intake
Closed valve
Broken rising main
Pump wear
Reverse rotation
Air or gas entry
Mechanical failure
A flow signal alone may not distinguish between these causes, but it provides valuable confirmation that the pump is producing water.
A discharge-pressure switch or pressure transmitter can identify abnormal loss of pressure.
Pressure monitoring is particularly useful in systems expected to maintain a defined discharge pressure.
Possible limitations include:
Pressure can remain temporarily trapped by a check valve.
A closed valve can create high pressure even when flow is absent.
A damaged rising main may change pressure unpredictably.
Pressure changes with tank level and system demand.
Startup pressure requires time to stabilize.
Pressure protection should be coordinated with flow, current and water-level signals where practical.
No single dry-running detection method is perfect.
For an important municipal, industrial, irrigation or fire-water installation, layered protection may include:
Low-water-level stop
Motor underload protection
Minimum-flow alarm
Low-discharge-pressure alarm
Motor temperature protection
Maximum run-time protection
Remote fault notification
Multiple signals help distinguish a falling well level from electrical, hydraulic and mechanical faults.
The control logic should identify which condition caused the shutdown so that operators do not repeatedly restart a damaged system.
The low-level sensor should stop the pump before the water reaches the intake.
Its elevation should account for:
Required submergence
Sensor accuracy
Water-level fluctuations
Turbulence during pumping
Pump intake position
Delay between detecting the condition and stopping the motor
Motor cooling requirements
Well drawdown rate
Placing the sensor immediately beside the intake provides almost no safety margin.
The required separation must be determined from the pump design and well conditions rather than from a universal distance.
If the pump stops at a low water level and restarts as soon as the water rises a few millimetres, it may enter rapid on-off cycling.
Repeated starting can overheat the motor and starter while preventing the well from recovering adequately.
A stable control arrangement normally uses either:
Separate stop and restart levels
A defined recovery time
Both level difference and recovery time
The restart level should be high enough to provide a useful volume of recovered water above the pump.
After a dry-running trip, the well needs time to recover.
The required delay depends on:
Well yield
Casing diameter
Drawdown
Aquifer recovery rate
Pump flow
Seasonal conditions
Required restart level
Do not choose a short delay only to restore service quickly.
If the pump repeatedly stops after a few minutes and restarts after a short delay, it may operate continuously in a damaging cycle.
Record recovery measurements during the pumping test and use them to establish a realistic delay.
Unlimited automatic restarting can conceal a serious problem and subject the pump to repeated stress.
A safer control sequence may:
Stop the pump when the dry-run condition is detected.
Record or display the cause.
Wait for a defined recovery period.
Confirm that the restart level or other conditions are satisfied.
Attempt a restart.
Verify that current, flow and pressure return to normal.
Lock out the system after a defined number of failed attempts.
The final settings depend on the application and the consequence of interrupted water supply.
A remote alarm may be appropriate for unattended systems.
A variable-frequency drive can control pump speed, but it does not automatically prevent dry running.
Some VFDs offer functions based on:
Low motor load
Minimum power
Pressure deviation
Flow estimation
Sleep mode
Pipe-fill sequence
Dry-pump detection
These functions must be configured for the actual pump and operating range.
At reduced speed, normal motor current and power may already be low. An incorrectly set threshold can cause nuisance trips or fail to detect loss of water.
The review should include:
Minimum permitted pump speed
Minimum continuous flow
Motor cooling at low speed
Normal load throughout the speed range
Pressure-setpoint logic
Dry-run detection delay
Restart sequence
Maximum restart attempts
Do not continuously increase VFD speed to maintain pressure when the well water level is falling. This can accelerate drawdown.
Downhole sensors operate in the same demanding environment as the pump cable.
The sensor cable may be exposed to:
Continuous immersion
Hydrostatic pressure
Abrasion
Cable-clamp pressure
Water chemistry
Electrical interference
Installation and retrieval stress
Use water-resistant cable and approved underwater joints.
Keep sensor wiring separated from motor power wiring where required to reduce electrical interference. Follow the control and sensor manufacturer’s grounding and shielding instructions.
Sensor cables should be secured without crushing them and should not carry the pump’s suspended weight.
A dry-running protection device is not complete until it has been tested under controlled conditions.
Commissioning should verify:
Correct sensor elevations
Accurate level indication
Proper stop signal
Motor shutdown time
Restart level
Recovery delay
Maximum restart attempts
Underload setting
Flow and pressure thresholds
Alarm output
Remote notification
Correct fault description
Manual reset function
Record normal operating values, including:
Static water level
Dynamic water level
Pump flow
Discharge pressure
Voltage
Motor current on each phase
Motor power where available
Pumping time before stabilization
Water-level recovery after shutdown
These baseline values make future troubleshooting much easier.
Sensors and relays can fail or drift over time.
Periodic inspection should include:
Level-sensor operation
Electrode condition
Float movement
Pressure-transducer calibration
Flowmeter or flow-switch operation
Underload relay setting
Alarm transmission
Control-panel terminals
Sensor-cable insulation
Restart timing
Event-history review
If a system never trips, that does not prove that the protection is working. Test it according to the equipment manufacturer’s procedure without deliberately damaging or running the pump dry.
Operators should investigate conditions such as:
Fluctuating discharge pressure
Flow falling during a pumping cycle
Air at the discharge
Sudden current reduction
Repeated low-level trips
Increasing recovery time
Pump vibration or noise
Sand content increasing after startup
Pressure failing to reach the setpoint
VFD speed rising while flow decreases
Frequent automatic restarts
Do not repeatedly reset the protection without identifying the cause.
Static level does not show the drawdown created by the operating pump.
A protection relay cannot make an unsustainable pumping rate suitable for the well.
The pump may already draw air before the control system stops it.
The well may not recover enough water to support another operating cycle.
Repeated dry-run cycles can damage the motor, starter and pump.
Low current can result from several hydraulic or mechanical faults.
Normal load varies by motor, pump model, head, flow, voltage and speed.
A setting that works during the wet season may be inadequate during drought.
This increases exposure to sediment and may obstruct cooling-water movement.
A flow sleeve improves the path of cooling water. It does not maintain the well level or replace a dry-running control.
Incorrect wiring, sensor placement or relay settings may remain unnoticed until the well level falls.
Assume a borehole pump must supply an irrigation storage tank.
A pumping test shows that the well level stabilizes at the required flow during normal conditions, but seasonal decline is expected.
The designer should:
Confirm the lowest expected dynamic water level.
Verify the selected pump flow against sustainable well yield.
Select a setting depth that maintains the required submergence.
Keep the motor safely above the well bottom and sediment zone.
Install a low-level stop sensor with adequate margin above the intake.
Install a separate restart sensor or define a verified recovery delay.
Configure underload protection from measured normal motor data.
Confirm discharge flow after every start.
Limit the number of automatic restart attempts.
Send an alarm if the pump cannot restore normal flow.
Record water level, current, flow and pressure during commissioning.
Review the settings during the dry season.
This arrangement uses the level sensor as the primary protection and motor-load and flow signals as confirmation.
Provide the following information to the pump and control supplier:
Complete pump and motor model
Required flow and head
Well depth
Pump installation depth
Static water level
Dynamic water level
Pumping-test flow and duration
Well recovery data
Minimum casing internal diameter
Screened or perforated intervals
Water inflow position
Distance from motor to well bottom
Water temperature
Sand content
Motor voltage, frequency and rated current
Starting method
VFD model, if applicable
Existing level sensors
Sensor cable length
Flowmeter or pressure-sensor details
Required restart time
Permitted automatic restart attempts
Remote monitoring requirements
Applicable electrical and water-system standards
Most conventional borehole pumps are not designed for dry operation. Loss of water can reduce cooling and lubrication and cause serious hydraulic or motor damage.
It can provide useful protection, but current or power changes can have several causes. Critical systems benefit from combining electrical monitoring with a water-level, flow or pressure signal.
It should stop the pump before the water reaches the minimum permitted submergence level. The exact elevation depends on the pump intake, manufacturer requirements, water-level fluctuation and shutdown delay.
The delay should be based on measured well-recovery behavior. There is no single restart time suitable for every borehole.
Only if suitable protection functions are correctly configured and verified. A VFD cannot supply water when the well yield is insufficient.
It may provide additional submergence, but it does not increase well yield. Excessive depth can increase sediment, pressure, cooling and installation risks.
No. A flow sleeve directs water along the motor for cooling. It cannot prevent the dynamic water level from falling below the pump.
Possible causes include insufficient well yield, a short recovery delay, sensors positioned too close together, incorrect underload settings or a hydraulic or electrical fault.
Automatic restart may be appropriate if the well normally recovers, but it should use a verified delay, confirmation of adequate water and a limit on failed restart attempts.
Reliable dry-running protection begins with correct pump and well design.
The system should:
Confirm well yield through pumping data.
Select a pump flow the well can sustain.
Use the dynamic water level to plan installation depth.
Maintain the manufacturer’s required submergence.
Keep the motor above the well bottom and sediment zone.
Stop the pump before the intake draws air.
Provide adequate well-recovery time.
Limit repeated automatic restarts.
Monitor level, motor load, flow or pressure as appropriate.
Test and document the protection settings.
Do not depend on one generic relay setting or assume that being underwater guarantees safe operation.
Final protection should be designed for the exact pump, motor, well response, control panel and operating schedule.
Send SLAPK your required flow and head, well depth, static and dynamic water levels, pumping-test data, pump setting depth, casing diameter, voltage, frequency, starting method and preferred protection arrangement.
Our engineers can recommend a suitable QJ or SP borehole pump and provide the motor, installation and control data required for a dry-running protection review.
Contact SLAPK for a borehole pump and protection recommendation
A deep well submersible pump must remain adequately submerged and supplied with enough water throughout operation.
If the well cannot replenish water as quickly as the pump removes it, the dynamic water level may continue falling. Once the water reaches the pump intake, the unit can begin drawing air, producing unstable flow or operating without sufficient water.
This condition is commonly called dry running.
Dry running can damage the pump, motor, bearings and other components. It may also produce severe vibration, overheating, loss of discharge pressure and repeated control-panel trips.
Reliable protection requires more than installing a single sensor. The system should combine:
Confirmed well yield
Correct pump capacity
Suitable installation depth
Adequate submergence
Water-level or electrical protection
Safe shutdown logic
Controlled automatic restart
Commissioning and periodic testing
Dry-running protection is a backup system. It does not make an oversized pump suitable for a low-yield well.
Dry running occurs when a pump operates without enough water passing through its hydraulic section and around the motor.
The condition does not always mean that the entire well is empty.
A borehole pump may experience dry-running conditions when:
The dynamic water level falls below the pump intake.
Water intermittently covers and exposes the intake.
The pump produces more water than the well can supply.
A level sensor is positioned incorrectly.
An inlet screen becomes blocked.
Air or gas enters the pump.
A valve is closed or a pipeline is obstructed.
The pump loses flow because of mechanical damage.
A tank pump creates a vortex and draws air.
A well requires more recovery time between operating cycles.
Partial loss of submergence can be damaging even before the pump becomes completely dry.
The intake may alternate between water and air, causing unstable pressure, vibration and rapid changes in motor load.
Water performs several functions while the pump is operating.
It is the pumped medium, but it can also contribute to:
Motor cooling
Bearing lubrication
Hydraulic stability
Heat removal from internal pump components
Stable thrust conditions
Cooling of mechanical seals in applicable designs
When water flow is lost, these functions are reduced or disappear.
Possible consequences include:
A submersible motor normally transfers heat to the surrounding moving water.
If the water level falls too far, the motor may lose its cooling environment. Even when the motor remains partly submerged, insufficient movement along its surface can allow temperature to rise.
Many borehole pump bearings and bushings depend on water for lubrication and cooling.
Operation with air, insufficient water or a mixture of air and water can increase friction and wear.
Some submersible pump designs use mechanical seals that depend on the surrounding liquid for cooling.
Running dry can overheat and damage the sealing faces.
A multistage borehole pump is designed to operate with water moving through its impellers and diffusers.
Loss of flow can change the internal pressure distribution and thrust conditions. Repeated dry-running cycles can shorten the service life of thrust bearings and hydraulic components.
Air entering the intake can create unstable hydraulic forces.
The pump may produce fluctuating flow, noise and vibration, potentially damaging:
Pump bearings
Motor bearings
Couplings
Rising-main connections
Electrical cable supports
Check valves
When the pump begins drawing air, discharge flow and pressure may fall.
The control system may respond by repeatedly starting the pump or increasing VFD speed, making the condition worse unless dry-running logic is included.
A pump can be capable of delivering more water than the well can sustainably produce.
For example, a pump may initially deliver the required flow while drawing water stored inside the casing. If aquifer inflow cannot maintain that rate, the water level will continue falling.
The pump may then reach the dry-running protection level even though its hydraulic performance is normal.
This is primarily a well-yield and pump-selection problem.
Static water level is measured while the well is resting.
After the pump starts, the water level normally falls to a dynamic or pumping level. The difference is the well drawdown.
Installing the pump according to static water level alone can leave insufficient submergence during operation.
Use the stabilized dynamic water level at the required pumping rate when reviewing installation depth and dry-running risk.
A water level measured during a wet season may not represent the lowest level expected during dry weather.
Groundwater conditions can also change because of:
Drought
Irrigation demand
Nearby pumping
Changes in recharge
New wells in the same aquifer
Long-term groundwater decline
Dry-running protection should account for the lowest credible operating level, not only the level observed on the installation date.
Sediment, mineral deposits, biological growth or debris can restrict water movement through the well screen or pump intake.
The well may contain water, but the pump may not receive enough flow.
A restriction can also change motor current and discharge pressure, causing symptoms similar to a falling water level.
A pump installed too shallow may become exposed when the dynamic water level falls.
Installing it deeper may increase the available submergence, but excessive depth creates other risks, including:
Reduced distance from the well bottom
Greater exposure to sand and sediment
Higher rising-main and cable cost
Greater suspended load
Higher pressure at lower pipe sections
More difficult retrieval
Possible installation below the productive screen
Inadequate motor cooling when inflow occurs from above
Installation depth must balance water coverage, well geometry, screen position, cooling and bottom clearance.
A pump installed in a tank, reservoir or open body of water may draw air through a surface vortex even when the intake remains below the normal water level.
Vortex formation depends on factors such as:
Submergence above the intake
Pump flow
Tank geometry
Distance from walls and floor
Intake orientation
Water-entry direction
Nearby pumps
Turbulence
A level sensor alone may not detect this condition because the tank still contains water.
Some wells contain dissolved or free gas.
Gas entering the pump can reduce hydraulic performance and cause fluctuating current, pressure and flow. The symptoms may resemble partial dry running.
The water source should be evaluated if air or gas continues to appear even when the measured water level remains above the pump.
Dry-running protection should begin with reliable well data.
A pumping test can establish:
Static water level
Dynamic water level at a stated flow
Drawdown
Recovery after shutdown
Whether the water level stabilizes
Approximate well capacity under the test conditions
Changes in water quality or sand content during pumping
The dynamic water level must always be recorded together with the pumping rate and elapsed time.
A statement such as “the water level is 50 metres" is incomplete unless it identifies whether the measurement is static or dynamic and how much water was being pumped.
If the water level continues falling throughout the test, the proposed operating flow may not be sustainable.
Dry-running controls can stop the pump, but they cannot increase the well’s water supply.
The selected duty flow should remain within the well’s verified operating capability.
Avoid selecting a pump only because it can deliver a higher maximum flow. An oversized pump may:
Lower the dynamic water level rapidly
Cause frequent dry-run trips
Increase sand movement
Create unstable cycling
Operate away from its efficient range
Require throttling
Increase starting and electrical stress
If demand is temporarily higher than the sustainable well flow, a storage tank may provide a better system arrangement.
The well pump can fill the tank at a controlled rate, while a separate booster pump supplies the variable or peak demand.
The pump must remain below the lowest expected dynamic water level by the minimum submergence specified for the selected model.
The required depth should be checked against:
Stabilized dynamic water level
Seasonal decline
Drawdown during peak demand
Nearby well interference
Pump intake position
Complete pump and motor length
Well screen or perforation position
Water inflow direction
Motor cooling requirements
Distance from the well bottom
Sand and sediment conditions
Do not confuse pump setting depth with pump head.
Installing the pump deeper does not directly increase the vertical lift from the pumping water level to the discharge point. It mainly changes the pump’s position within the well and the available submergence.
The referenced SLAPK QJ installation instructions state that the first-stage impeller should be at least 2 metres below the dynamic water level and that the motor bottom should remain at least 3 metres above the well bottom. They also provide a model-specific limit for immersion below static water level.
These values are product instructions for the referenced QJ configuration, not universal limits for every borehole pump. Confirm the exact requirements for the ordered pump and motor.
Conductive level electrodes are commonly used in water wells.
A typical arrangement can include:
A low-level stop electrode
A higher restart electrode
A common reference electrode where required
A level relay in the control panel
When the water falls to the stop level, the control system opens the motor circuit and stops the pump.
The pump should not restart as soon as water touches the same electrode again. A separate restart level or time delay provides hysteresis and allows the well to recover.
Electrode suitability depends on water conductivity. Very low-conductivity water, scale or deposits can reduce reliability.
The supplier should confirm:
Electrode material
Cable type
Control voltage
Water-conductivity range
Maximum cable length
Installation depth
Spacing between electrodes
Resistance to corrosion and deposits
Float switches are widely used in tanks, sumps and reservoirs.
They can provide a direct low-level signal, but they are often impractical in narrow boreholes because they require space to move freely.
A float may become obstructed by:
The rising main
Power cable
Cable clamps
Well casing
Other sensors
Turbulence
Sediment
Use a float only where the installation provides adequate clearance and the device is approved for the liquid and depth.
A submersible pressure transducer can measure the water column above the sensor.
It may provide continuous level information rather than a simple wet-or-dry signal.
Advantages can include:
Adjustable stop and restart levels
Continuous trend monitoring
Remote telemetry
Seasonal water-level records
Alarm functions
Pumping-test data
However, the indicated level can be affected by:
Sensor elevation
Water density
Atmospheric-pressure compensation
Cable vent condition
Temperature
Calibration drift
Electrical noise
Incorrect reference datum
The transducer should be installed at a known elevation and protected from direct mechanical damage.
A submersible motor normally draws less power when the pump loses hydraulic load.
An electronic motor-protection relay may detect dry running by monitoring:
Current
Active power
Power factor
Motor load
A calculated combination of electrical values
This method can be useful because it does not require a separate downhole water-level cable.
However, low current does not uniquely prove dry running.
Similar readings can result from:
Closed or restricted intake
Broken pump shaft
Worn impellers
Gas entering the pump
Incorrect voltage
Incorrect VFD frequency
Motor or cable faults
Pump operation at an unusual point on its curve
The protection threshold should therefore be commissioned using measured data from the actual pump under normal operating conditions.
Do not copy a current setting from a different motor or pump.
A flow switch or flowmeter can detect loss of water delivery.
This is useful where dry running produces a clear reduction in discharge flow.
The logic should allow for the short period between motor starting and stable flow reaching the sensor. Without a suitable startup delay, the system may trip every time the pump starts.
Flow monitoring can also detect problems that a water-level sensor may miss, including:
Blocked intake
Closed valve
Broken rising main
Pump wear
Reverse rotation
Air or gas entry
Mechanical failure
A flow signal alone may not distinguish between these causes, but it provides valuable confirmation that the pump is producing water.
A discharge-pressure switch or pressure transmitter can identify abnormal loss of pressure.
Pressure monitoring is particularly useful in systems expected to maintain a defined discharge pressure.
Possible limitations include:
Pressure can remain temporarily trapped by a check valve.
A closed valve can create high pressure even when flow is absent.
A damaged rising main may change pressure unpredictably.
Pressure changes with tank level and system demand.
Startup pressure requires time to stabilize.
Pressure protection should be coordinated with flow, current and water-level signals where practical.
No single dry-running detection method is perfect.
For an important municipal, industrial, irrigation or fire-water installation, layered protection may include:
Low-water-level stop
Motor underload protection
Minimum-flow alarm
Low-discharge-pressure alarm
Motor temperature protection
Maximum run-time protection
Remote fault notification
Multiple signals help distinguish a falling well level from electrical, hydraulic and mechanical faults.
The control logic should identify which condition caused the shutdown so that operators do not repeatedly restart a damaged system.
The low-level sensor should stop the pump before the water reaches the intake.
Its elevation should account for:
Required submergence
Sensor accuracy
Water-level fluctuations
Turbulence during pumping
Pump intake position
Delay between detecting the condition and stopping the motor
Motor cooling requirements
Well drawdown rate
Placing the sensor immediately beside the intake provides almost no safety margin.
The required separation must be determined from the pump design and well conditions rather than from a universal distance.
If the pump stops at a low water level and restarts as soon as the water rises a few millimetres, it may enter rapid on-off cycling.
Repeated starting can overheat the motor and starter while preventing the well from recovering adequately.
A stable control arrangement normally uses either:
Separate stop and restart levels
A defined recovery time
Both level difference and recovery time
The restart level should be high enough to provide a useful volume of recovered water above the pump.
After a dry-running trip, the well needs time to recover.
The required delay depends on:
Well yield
Casing diameter
Drawdown
Aquifer recovery rate
Pump flow
Seasonal conditions
Required restart level
Do not choose a short delay only to restore service quickly.
If the pump repeatedly stops after a few minutes and restarts after a short delay, it may operate continuously in a damaging cycle.
Record recovery measurements during the pumping test and use them to establish a realistic delay.
Unlimited automatic restarting can conceal a serious problem and subject the pump to repeated stress.
A safer control sequence may:
Stop the pump when the dry-run condition is detected.
Record or display the cause.
Wait for a defined recovery period.
Confirm that the restart level or other conditions are satisfied.
Attempt a restart.
Verify that current, flow and pressure return to normal.
Lock out the system after a defined number of failed attempts.
The final settings depend on the application and the consequence of interrupted water supply.
A remote alarm may be appropriate for unattended systems.
A variable-frequency drive can control pump speed, but it does not automatically prevent dry running.
Some VFDs offer functions based on:
Low motor load
Minimum power
Pressure deviation
Flow estimation
Sleep mode
Pipe-fill sequence
Dry-pump detection
These functions must be configured for the actual pump and operating range.
At reduced speed, normal motor current and power may already be low. An incorrectly set threshold can cause nuisance trips or fail to detect loss of water.
The review should include:
Minimum permitted pump speed
Minimum continuous flow
Motor cooling at low speed
Normal load throughout the speed range
Pressure-setpoint logic
Dry-run detection delay
Restart sequence
Maximum restart attempts
Do not continuously increase VFD speed to maintain pressure when the well water level is falling. This can accelerate drawdown.
Downhole sensors operate in the same demanding environment as the pump cable.
The sensor cable may be exposed to:
Continuous immersion
Hydrostatic pressure
Abrasion
Cable-clamp pressure
Water chemistry
Electrical interference
Installation and retrieval stress
Use water-resistant cable and approved underwater joints.
Keep sensor wiring separated from motor power wiring where required to reduce electrical interference. Follow the control and sensor manufacturer’s grounding and shielding instructions.
Sensor cables should be secured without crushing them and should not carry the pump’s suspended weight.
A dry-running protection device is not complete until it has been tested under controlled conditions.
Commissioning should verify:
Correct sensor elevations
Accurate level indication
Proper stop signal
Motor shutdown time
Restart level
Recovery delay
Maximum restart attempts
Underload setting
Flow and pressure thresholds
Alarm output
Remote notification
Correct fault description
Manual reset function
Record normal operating values, including:
Static water level
Dynamic water level
Pump flow
Discharge pressure
Voltage
Motor current on each phase
Motor power where available
Pumping time before stabilization
Water-level recovery after shutdown
These baseline values make future troubleshooting much easier.
Sensors and relays can fail or drift over time.
Periodic inspection should include:
Level-sensor operation
Electrode condition
Float movement
Pressure-transducer calibration
Flowmeter or flow-switch operation
Underload relay setting
Alarm transmission
Control-panel terminals
Sensor-cable insulation
Restart timing
Event-history review
If a system never trips, that does not prove that the protection is working. Test it according to the equipment manufacturer’s procedure without deliberately damaging or running the pump dry.
Operators should investigate conditions such as:
Fluctuating discharge pressure
Flow falling during a pumping cycle
Air at the discharge
Sudden current reduction
Repeated low-level trips
Increasing recovery time
Pump vibration or noise
Sand content increasing after startup
Pressure failing to reach the setpoint
VFD speed rising while flow decreases
Frequent automatic restarts
Do not repeatedly reset the protection without identifying the cause.
Static level does not show the drawdown created by the operating pump.
A protection relay cannot make an unsustainable pumping rate suitable for the well.
The pump may already draw air before the control system stops it.
The well may not recover enough water to support another operating cycle.
Repeated dry-run cycles can damage the motor, starter and pump.
Low current can result from several hydraulic or mechanical faults.
Normal load varies by motor, pump model, head, flow, voltage and speed.
A setting that works during the wet season may be inadequate during drought.
This increases exposure to sediment and may obstruct cooling-water movement.
A flow sleeve improves the path of cooling water. It does not maintain the well level or replace a dry-running control.
Incorrect wiring, sensor placement or relay settings may remain unnoticed until the well level falls.
Assume a borehole pump must supply an irrigation storage tank.
A pumping test shows that the well level stabilizes at the required flow during normal conditions, but seasonal decline is expected.
The designer should:
Confirm the lowest expected dynamic water level.
Verify the selected pump flow against sustainable well yield.
Select a setting depth that maintains the required submergence.
Keep the motor safely above the well bottom and sediment zone.
Install a low-level stop sensor with adequate margin above the intake.
Install a separate restart sensor or define a verified recovery delay.
Configure underload protection from measured normal motor data.
Confirm discharge flow after every start.
Limit the number of automatic restart attempts.
Send an alarm if the pump cannot restore normal flow.
Record water level, current, flow and pressure during commissioning.
Review the settings during the dry season.
This arrangement uses the level sensor as the primary protection and motor-load and flow signals as confirmation.
Provide the following information to the pump and control supplier:
Complete pump and motor model
Required flow and head
Well depth
Pump installation depth
Static water level
Dynamic water level
Pumping-test flow and duration
Well recovery data
Minimum casing internal diameter
Screened or perforated intervals
Water inflow position
Distance from motor to well bottom
Water temperature
Sand content
Motor voltage, frequency and rated current
Starting method
VFD model, if applicable
Existing level sensors
Sensor cable length
Flowmeter or pressure-sensor details
Required restart time
Permitted automatic restart attempts
Remote monitoring requirements
Applicable electrical and water-system standards
Most conventional borehole pumps are not designed for dry operation. Loss of water can reduce cooling and lubrication and cause serious hydraulic or motor damage.
It can provide useful protection, but current or power changes can have several causes. Critical systems benefit from combining electrical monitoring with a water-level, flow or pressure signal.
It should stop the pump before the water reaches the minimum permitted submergence level. The exact elevation depends on the pump intake, manufacturer requirements, water-level fluctuation and shutdown delay.
The delay should be based on measured well-recovery behavior. There is no single restart time suitable for every borehole.
Only if suitable protection functions are correctly configured and verified. A VFD cannot supply water when the well yield is insufficient.
It may provide additional submergence, but it does not increase well yield. Excessive depth can increase sediment, pressure, cooling and installation risks.
No. A flow sleeve directs water along the motor for cooling. It cannot prevent the dynamic water level from falling below the pump.
Possible causes include insufficient well yield, a short recovery delay, sensors positioned too close together, incorrect underload settings or a hydraulic or electrical fault.
Automatic restart may be appropriate if the well normally recovers, but it should use a verified delay, confirmation of adequate water and a limit on failed restart attempts.
Reliable dry-running protection begins with correct pump and well design.
The system should:
Confirm well yield through pumping data.
Select a pump flow the well can sustain.
Use the dynamic water level to plan installation depth.
Maintain the manufacturer’s required submergence.
Keep the motor above the well bottom and sediment zone.
Stop the pump before the intake draws air.
Provide adequate well-recovery time.
Limit repeated automatic restarts.
Monitor level, motor load, flow or pressure as appropriate.
Test and document the protection settings.
Do not depend on one generic relay setting or assume that being underwater guarantees safe operation.
Final protection should be designed for the exact pump, motor, well response, control panel and operating schedule.
Send SLAPK your required flow and head, well depth, static and dynamic water levels, pumping-test data, pump setting depth, casing diameter, voltage, frequency, starting method and preferred protection arrangement.
Our engineers can recommend a suitable QJ or SP borehole pump and provide the motor, installation and control data required for a dry-running protection review.
Contact SLAPK for a borehole pump and protection recommendation
