The main function of a limit switch sensor in an injection molding machine π is to detect the position of a moving part and send a signal to the controller when that position is reached π‘.
Common uses include:
Mold open/close position detection π§
* Confirms the mold is fully open or fully closed.
* Prevents the next operation from starting until the correct position is reached β .
Safety interlocking π
* Stops machine movement if a component moves beyond its allowed travel.
* Helps protect the mold and machine from damage π‘οΈ.
Ejector position detection π
* Confirms the ejector is fully forward or fully retracted.
Core pull position detection βοΈ
* Verifies hydraulic cores are in the correct position before mold movement or injection.
Automatic sequence control π
* Triggers the next step in the molding cycle when a specific position is reached.
Simple Example π‘
When the mold closes, a limit switch may be activated at the fully closed position. The machine controller receives this signal and allows the clamping pressure build-up and injection process to start β‘. Without that signal, injection is blocked to prevent mold damage π«.
Common uses include:
Mold open/close position detection π§
* Confirms the mold is fully open or fully closed.
* Prevents the next operation from starting until the correct position is reached β .
Safety interlocking π
* Stops machine movement if a component moves beyond its allowed travel.
* Helps protect the mold and machine from damage π‘οΈ.
Ejector position detection π
* Confirms the ejector is fully forward or fully retracted.
Core pull position detection βοΈ
* Verifies hydraulic cores are in the correct position before mold movement or injection.
Automatic sequence control π
* Triggers the next step in the molding cycle when a specific position is reached.
Simple Example π‘
When the mold closes, a limit switch may be activated at the fully closed position. The machine controller receives this signal and allows the clamping pressure build-up and injection process to start β‘. Without that signal, injection is blocked to prevent mold damage π«.
For an injection molding machine there are different types of sensor and functions ππ§
The most critical sensors are:
Mold position sensors β tell the controller where the mold is π
Injection position sensor β measures screw/injection movement π
Ejector position sensor β monitors ejector stroke βοΈ
Hydraulic pressure sensors β control clamping and injection pressure π§π₯
Barrel thermocouples β control zone temperatures π‘οΈ
Oil temperature sensor β protects the hydraulic system from overheating π‘οΈπ‘οΈ
The most critical sensors are:
Mold position sensors β tell the controller where the mold is π
Injection position sensor β measures screw/injection movement π
Ejector position sensor β monitors ejector stroke βοΈ
Hydraulic pressure sensors β control clamping and injection pressure π§π₯
Barrel thermocouples β control zone temperatures π‘οΈ
Oil temperature sensor β protects the hydraulic system from overheating π‘οΈπ‘οΈ
Engineering world
Types of relays in injection molding machine βοΈ Injection molding machines use many different types of relays to control motors, heaters, valves, alarms, and safety circuits. The most common types are: 1. Electromagnetic Relay (Control Relay) π Purpose:β¦
Main Functions of a Control Relay π οΈ
Signal Amplification π
A low-current signal from the PLC, timer, limit switch, or sensor activates the relay. The relay then switches a higher-current load such as a solenoid valve, contactor, alarm, or motor circuit. β‘
Electrical Isolation π
Protects the PLC and electronic control circuits from high-voltage or high-current devices. π‘οΈ
Logic Control π§
Used to create interlocks and sequence operations.
Example: The machine will not start injection unless the mold-close confirmation relay is energized. π«π§
Multiple Contact Switching π
One relay can control several circuits simultaneously using its NO (Normally Open) and NC (Normally Closed) contacts.
Example in an Injection Molding Machine π
When the mold reaches the fully closed position:
1. A limit switch or proximity sensor sends a signal. π‘
2. The PLC energizes a control relay. π
3. The relay activates the hydraulic solenoid valve for injection. π§
Injection starts only after mold-close confirmation. β
Typical Applications π
- Mold open/close control
- Injection sequence control
- Ejector operation
- Hydraulic valve switching
- Heater and cooling interlocks π₯βοΈ
- Alarm circuits π
- Safety circuits π
How to Identify a Control Relay π
A control relay usually has:
- A coil (terminals often marked A1 and A2) π
- Several NO and NC contacts (e.g., 13-14, 21-22) π
- Transparent or plug-in housing in the electrical cabinet π¦
Signal Amplification π
A low-current signal from the PLC, timer, limit switch, or sensor activates the relay. The relay then switches a higher-current load such as a solenoid valve, contactor, alarm, or motor circuit. β‘
Electrical Isolation π
Protects the PLC and electronic control circuits from high-voltage or high-current devices. π‘οΈ
Logic Control π§
Used to create interlocks and sequence operations.
Example: The machine will not start injection unless the mold-close confirmation relay is energized. π«π§
Multiple Contact Switching π
One relay can control several circuits simultaneously using its NO (Normally Open) and NC (Normally Closed) contacts.
Example in an Injection Molding Machine π
When the mold reaches the fully closed position:
1. A limit switch or proximity sensor sends a signal. π‘
2. The PLC energizes a control relay. π
3. The relay activates the hydraulic solenoid valve for injection. π§
Injection starts only after mold-close confirmation. β
Typical Applications π
- Mold open/close control
- Injection sequence control
- Ejector operation
- Hydraulic valve switching
- Heater and cooling interlocks π₯βοΈ
- Alarm circuits π
- Safety circuits π
How to Identify a Control Relay π
A control relay usually has:
- A coil (terminals often marked A1 and A2) π
- Several NO and NC contacts (e.g., 13-14, 21-22) π
- Transparent or plug-in housing in the electrical cabinet π¦
A Solid State Relay (SSR) in an injection molding machine performs the same basic job as a mechanical relayβit switches electrical power ON and OFFβbut it does so electronically with no moving contacts. β‘π§
Main Functions of SSR in an Injection Molding Machine
Heater Temperature Control π₯
Most commonly used for barrel heater bands and nozzle heaters.
Receives a low-voltage control signal from the temperature controller or PLC.
Switches the high-power AC supply to the heaters ON and OFF rapidly to maintain the set temperature. π‘οΈ
Improved Temperature Stability π
SSRs can switch many times per second. β‘
This allows more precise control of barrel zones, resulting in:
Better melt quality
More consistent shot weight π―
Reduced temperature fluctuations
Long Service Life βΎοΈ
No mechanical contacts to wear out.
Suitable for continuous operation in molding machines where heaters cycle constantly.
Silent Operation π€«
Unlike electromagnetic relays, SSRs do not make a clicking sound when switching.
Advantages Over Mechanical Relays βοΈ
Solid State Relay vs Mechanical Relay
No moving parts vs Has moving contacts
Silent vs Clicking noise π
Fast switching vs Slower switching β±οΈ
Long life vs Contacts wear out
Best for heaters vs Good for general switching
Common SSR Failure Symptoms π¨
Heater always ON π₯
SSR shorted internally.
Barrel temperature keeps rising above setpoint.
Heater never ON βοΈ
SSR open circuit or no control signal.
Temperature cannot reach setpoint.
Intermittent heating β οΈ
Loose wiring, overheating SSR, or damaged controller output.
How to Identify an SSR π
It usually has:
Input terminals: + and β (control signal from PLC/temperature controller)
Output terminals: 1 and 2 or L and T (power to heater) π
Mounted on an aluminum heat sink because SSRs generate heat. π‘οΈ
Main Functions of SSR in an Injection Molding Machine
Heater Temperature Control π₯
Most commonly used for barrel heater bands and nozzle heaters.
Receives a low-voltage control signal from the temperature controller or PLC.
Switches the high-power AC supply to the heaters ON and OFF rapidly to maintain the set temperature. π‘οΈ
Improved Temperature Stability π
SSRs can switch many times per second. β‘
This allows more precise control of barrel zones, resulting in:
Better melt quality
More consistent shot weight π―
Reduced temperature fluctuations
Long Service Life βΎοΈ
No mechanical contacts to wear out.
Suitable for continuous operation in molding machines where heaters cycle constantly.
Silent Operation π€«
Unlike electromagnetic relays, SSRs do not make a clicking sound when switching.
Advantages Over Mechanical Relays βοΈ
Solid State Relay vs Mechanical Relay
No moving parts vs Has moving contacts
Silent vs Clicking noise π
Fast switching vs Slower switching β±οΈ
Long life vs Contacts wear out
Best for heaters vs Good for general switching
Common SSR Failure Symptoms π¨
Heater always ON π₯
SSR shorted internally.
Barrel temperature keeps rising above setpoint.
Heater never ON βοΈ
SSR open circuit or no control signal.
Temperature cannot reach setpoint.
Intermittent heating β οΈ
Loose wiring, overheating SSR, or damaged controller output.
How to Identify an SSR π
It usually has:
Input terminals: + and β (control signal from PLC/temperature controller)
Output terminals: 1 and 2 or L and T (power to heater) π
Mounted on an aluminum heat sink because SSRs generate heat. π‘οΈ
Difference between limit switch and proximity sensor
Limit Switch π
Has a lever, roller, or plunger that must be physically pressed.
Used where direct contact is acceptable.
Example: Detecting full mold open or ejector end position on older machines.
Proximity Sensor π
Detects metal (inductive), plastic/liquid (capacitive), or objects without touching them.
Faster and more reliable.
Common on modern injection molding machines for mold position, carriage position, and safety monitoring.
Wiring π
Limit Switch
COM (Common)
NO (Normally Open)
NC (Normally Closed)
Proximity Sensor
Brown = +24V
Blue = 0V
Black = Output (most common 3-wire DC type)
Limit Switch π
Has a lever, roller, or plunger that must be physically pressed.
Used where direct contact is acceptable.
Example: Detecting full mold open or ejector end position on older machines.
Proximity Sensor π
Detects metal (inductive), plastic/liquid (capacitive), or objects without touching them.
Faster and more reliable.
Common on modern injection molding machines for mold position, carriage position, and safety monitoring.
Wiring π
Limit Switch
COM (Common)
NO (Normally Open)
NC (Normally Closed)
Proximity Sensor
Brown = +24V
Blue = 0V
Black = Output (most common 3-wire DC type)
The main difference between PNP and NPN proximity sensors is the way they switch the output signal. π
PNP Sensor (Sourcing Output) π
When the sensor detects an object, the output wire provides +24 VDC (positive voltage) to the PLC or load. β‘
Current flows from the sensor to the load. β‘οΈ
Commonly used in Europe and many modern PLC systems. πͺπΊ
Typical wiring:
Brown = +24 V π€
Blue = 0 V π΅
Black (output) = +24 V when activated β«
+24V β Sensor ββΊ PLC Input π‘
NPN Sensor (Sinking Output) β¬οΈ
When the sensor detects an object, the output wire connects to 0 V (ground). π
Current flows from the load into the sensor. β¬οΈ
Commonly used in many Asian systems. π
Typical wiring:
Brown = +24 V π€
Blue = 0 V π΅
Black (output) = 0 V when activated β«
PLC Input ββΊ Sensor β 0V π‘
PNP Sensor (Sourcing Output) π
When the sensor detects an object, the output wire provides +24 VDC (positive voltage) to the PLC or load. β‘
Current flows from the sensor to the load. β‘οΈ
Commonly used in Europe and many modern PLC systems. πͺπΊ
Typical wiring:
Brown = +24 V π€
Blue = 0 V π΅
Black (output) = +24 V when activated β«
+24V β Sensor ββΊ PLC Input π‘
NPN Sensor (Sinking Output) β¬οΈ
When the sensor detects an object, the output wire connects to 0 V (ground). π
Current flows from the load into the sensor. β¬οΈ
Commonly used in many Asian systems. π
Typical wiring:
Brown = +24 V π€
Blue = 0 V π΅
Black (output) = 0 V when activated β«
PLC Input ββΊ Sensor β 0V π‘
Types of contactor in an injection molding machine and functions βοΈβ‘
In an injection molding machine, contactors are electromagnetic switches that control high-power electrical loads such as motors, heaters, and pumps. The most common contactors and their functions are:
1. Main Contactor (MC) π
Connects the machine to the main three-phase power supply.
Energizes the entire electrical system after the Start button is pressed.
Opens immediately during an emergency stop or fault. π
2. Hydraulic Pump Motor Contactor π§
Starts and stops the hydraulic pump motor.
Operates according to machine commands to provide hydraulic pressure.
3. Heater Contactor π₯
Supplies power to the barrel and nozzle heaters.
Turns heaters ON and OFF based on temperature controller signals.
4. Clamp Motor Contactor (Electric Machines) π©
Controls the motor that opens and closes the mold.
Used mainly in all-electric injection molding machines.
5. Screw/Injection Motor Contactor π
Controls the motor that rotates the screw for plasticizing and injection.
6. Cooling Fan Contactor βοΈ
Powers cabinet cooling fans or oil cooler fans.
Prevents electrical components from overheating.
7. Reversing Contactor (Forward/Reverse) β¬ οΈβ‘οΈ
Uses two interlocked contactors:
Forward (FWD) β rotates the motor in the forward direction.
Reverse (REV) β rotates the motor in the opposite direction.
Commonly used for motors that require bidirectional operation.
8. StarβDelta Contactors βπΊ
Used on large hydraulic pump motors to reduce starting current:
Main Contactor β connects the motor to the supply.
Star Contactor β starts the motor in star connection.
Delta Contactor β switches the motor to delta after a few seconds for full power.
9. Vacuum Contactor (High-Power Machines) β‘
Used in very large injection molding machines.
Switches high currents with minimal electrical arcing.
In an injection molding machine, contactors are electromagnetic switches that control high-power electrical loads such as motors, heaters, and pumps. The most common contactors and their functions are:
1. Main Contactor (MC) π
Connects the machine to the main three-phase power supply.
Energizes the entire electrical system after the Start button is pressed.
Opens immediately during an emergency stop or fault. π
2. Hydraulic Pump Motor Contactor π§
Starts and stops the hydraulic pump motor.
Operates according to machine commands to provide hydraulic pressure.
3. Heater Contactor π₯
Supplies power to the barrel and nozzle heaters.
Turns heaters ON and OFF based on temperature controller signals.
4. Clamp Motor Contactor (Electric Machines) π©
Controls the motor that opens and closes the mold.
Used mainly in all-electric injection molding machines.
5. Screw/Injection Motor Contactor π
Controls the motor that rotates the screw for plasticizing and injection.
6. Cooling Fan Contactor βοΈ
Powers cabinet cooling fans or oil cooler fans.
Prevents electrical components from overheating.
7. Reversing Contactor (Forward/Reverse) β¬ οΈβ‘οΈ
Uses two interlocked contactors:
Forward (FWD) β rotates the motor in the forward direction.
Reverse (REV) β rotates the motor in the opposite direction.
Commonly used for motors that require bidirectional operation.
8. StarβDelta Contactors βπΊ
Used on large hydraulic pump motors to reduce starting current:
Main Contactor β connects the motor to the supply.
Star Contactor β starts the motor in star connection.
Delta Contactor β switches the motor to delta after a few seconds for full power.
9. Vacuum Contactor (High-Power Machines) β‘
Used in very large injection molding machines.
Switches high currents with minimal electrical arcing.
A Star-Delta starter is used to start a three-phase induction motor with reduced starting current β‘. It is commonly used for large motors, including hydraulic pumps π, compressors, fans π, and some injection molding machines. During startup, the motor is connected in Star (Y), then automatically changes to Delta (Ξ) after a few seconds. This reduces electrical and mechanical stress on the motor.
Three contactors in a Star-Delta starter:
1οΈβ£ Main Contactor (KM1)
- Connects the three-phase power supply to the motor π.
- Remains ON during both Star and Delta operation.
- Acts as the main power switching contactor.
2οΈβ£ Star Contactor (KM2)
- Connects the motor windings in Star (Y).
- Used only during starting.
- Reduces the voltage across each winding to about 58% (1/β3) of the line voltage, reducing starting current and starting torque.
3οΈβ£ Delta Contactor (KM3)
- Connects the motor windings in Delta (Ξ).
- Turns ON after the timer finishes β±οΈ.
- Allows the motor to receive full line voltage and produce full torque and power for normal operation.
Sequence of operation:
1. Start button pressed βΆοΈ.
2. Main contactor = ON.
3. Star contactor = ON.
4. Delta contactor = OFF.
5. Motor starts with low current.
6. After 3β10 seconds (timer setting) β³.
7. Star contactor = OFF.
8. Delta contactor = ON.
9. Main contactor stays ON.
10. Motor runs at full speed and full power π.
Advantages:
- Reduces starting current β‘.
- Reduces voltage drop in the power supply.
- Protects the motor from electrical and mechanical stress.
- Increases motor life π‘οΈ.
Disadvantages:
- Starting torque is only about one-third of direct-on-line (DOL) starting.
- Not suitable for heavy-load starting.
- Requires a motor with six terminals designed for Star-Delta starting π§.
Three contactors in a Star-Delta starter:
1οΈβ£ Main Contactor (KM1)
- Connects the three-phase power supply to the motor π.
- Remains ON during both Star and Delta operation.
- Acts as the main power switching contactor.
2οΈβ£ Star Contactor (KM2)
- Connects the motor windings in Star (Y).
- Used only during starting.
- Reduces the voltage across each winding to about 58% (1/β3) of the line voltage, reducing starting current and starting torque.
3οΈβ£ Delta Contactor (KM3)
- Connects the motor windings in Delta (Ξ).
- Turns ON after the timer finishes β±οΈ.
- Allows the motor to receive full line voltage and produce full torque and power for normal operation.
Sequence of operation:
1. Start button pressed βΆοΈ.
2. Main contactor = ON.
3. Star contactor = ON.
4. Delta contactor = OFF.
5. Motor starts with low current.
6. After 3β10 seconds (timer setting) β³.
7. Star contactor = OFF.
8. Delta contactor = ON.
9. Main contactor stays ON.
10. Motor runs at full speed and full power π.
Advantages:
- Reduces starting current β‘.
- Reduces voltage drop in the power supply.
- Protects the motor from electrical and mechanical stress.
- Increases motor life π‘οΈ.
Disadvantages:
- Starting torque is only about one-third of direct-on-line (DOL) starting.
- Not suitable for heavy-load starting.
- Requires a motor with six terminals designed for Star-Delta starting π§.
A screw compressor (also called a rotary screw compressor) π works by using two intermeshing helical screws to compress air or gas continuously. Hereβs the principle explained in a simple, practical way:
π§ Basic Working Principle
The compressor has two main rotating parts:
- Male rotor (driving screw) π¦Έ
- Female rotor (driven screw) π¦Ή
These rotors mesh together inside a casing. ποΈ
βοΈ Step-by-Step Operation
1. Air Intake (Suction) π¬οΈ
Air enters through the inlet valve.
The space between the screw threads (lobes) opens and traps air. πͺ€
2. Air Trapping π
As the rotors turn, the trapped air is sealed between:
- The screw lobes
- The casing wall
3. Compression π
The screws continue rotating.
The space holding the air becomes smaller (volume reduces).
According to the Ideal Gas Law, when volume decreases β pressure increases. β¬οΈ
This is how air gets compressed. π¨
4. Discharge (Outlet) πͺ
When the compressed air reaches the outlet port:
It is released at high pressure. π₯
The cycle continues smoothly and continuously (no pulsation like piston compressors). π
π Key Characteristics
- Continuous flow (no start-stop like reciprocating compressor) π
- Low vibration π€«
- High efficiency for industrial use π
Can be:
- Oil-injected type (for cooling & sealing) π’οΈ
- Oil-free type (for clean air applications) π§Ό
π§ Basic Working Principle
The compressor has two main rotating parts:
- Male rotor (driving screw) π¦Έ
- Female rotor (driven screw) π¦Ή
These rotors mesh together inside a casing. ποΈ
βοΈ Step-by-Step Operation
1. Air Intake (Suction) π¬οΈ
Air enters through the inlet valve.
The space between the screw threads (lobes) opens and traps air. πͺ€
2. Air Trapping π
As the rotors turn, the trapped air is sealed between:
- The screw lobes
- The casing wall
3. Compression π
The screws continue rotating.
The space holding the air becomes smaller (volume reduces).
According to the Ideal Gas Law, when volume decreases β pressure increases. β¬οΈ
This is how air gets compressed. π¨
4. Discharge (Outlet) πͺ
When the compressed air reaches the outlet port:
It is released at high pressure. π₯
The cycle continues smoothly and continuously (no pulsation like piston compressors). π
π Key Characteristics
- Continuous flow (no start-stop like reciprocating compressor) π
- Low vibration π€«
- High efficiency for industrial use π
Can be:
- Oil-injected type (for cooling & sealing) π’οΈ
- Oil-free type (for clean air applications) π§Ό
A centrifugal pump is a mechanical device designed to move fluids (liquids) by converting rotational kinetic energy into hydrodynamic energy of the fluid flow. The rotational energy typically comes from an electric motor, engine, or turbine.
It is the most common type of pump used in industrial, agricultural, and domestic applications due to its simple design, high efficiency, and consistent discharge.
ββββββββββ
1. Major Components of a Centrifugal Pump
To understand how it works, it is essential to know its key parts:
1. The Impeller (The Rotating Part):
A wheel with backward-curved vanes or blades. It rotates at high speeds, transferring kinetic energy directly to the fluid. Impellers can be:
β’ Closed: Vanes are sandwiched between two discs (most efficient, used for clean water).
β’ Semi-open: Vanes are attached to one disc (used for slightly dirty water).
β’ Open: Vanes are open on both sides (used for slurries and thick liquids).
2. The Casing (The Stationary Part):
An airtight passage surrounding the impeller. It is designed to guide the fluid from the inlet to the outlet and convert kinetic energy (speed) into pressure. The most common type is a Volute Casing (a spiral-shaped casing with a gradually increasing cross-sectional area).
1.
The Suction Pipe (Inlet):
The pipe connected to the center (called the "eye") of the impeller, through which fluid enters the pump.
2.
The Delivery Pipe (Outlet):
The pipe through which the pressurized fluid is discharged. It usually features a control valve to regulate flow.
3.
Shaft and Bearings:
The shaft connects the impeller to the motor. Bearings support the rotating shaft and reduce friction.
4.
Shaft Seal (Stuffing Box/Mechanical Seal):
Prevents liquid from leaking out of the pump casing along the rotating shaft.
ββββββββββ
2. The Working Principle (Step-by-Step)
The working principle of a centrifugal pump is based on centrifugal force. When a body of liquid is rotated by an external force, it is thrown away from the center of rotation, creating pressure.
Here is the step-by-step process of how it operates:
Step 1: Priming
Before starting the pump, the suction pipe and casing must be completely filled with the liquid to be pumped (a process called priming). If there is air inside, the pump cannot create the vacuum needed to lift the liquid because air has a much lower density than water, meaning the centrifugal force generated on air is negligible.
Step 2: Rotation of the Impeller
When the electric motor is turned on, it rotates the impeller at high speed inside the water-filled casing.
Step 3: Generation of Centrifugal Force
As the impeller rotates, the liquid trapped between its vanes is forced to rotate with it. The rotation subjects the liquid to centrifugal force, which flings the liquid radially outward toward the outer edge of the impeller.
Step 4: Vacuum Creation at the "Eye"
Because the liquid is thrown outward, a localized low-pressure zone (vacuum) is created at the center of the impeller (the "eye").
It is the most common type of pump used in industrial, agricultural, and domestic applications due to its simple design, high efficiency, and consistent discharge.
ββββββββββ
1. Major Components of a Centrifugal Pump
To understand how it works, it is essential to know its key parts:
1. The Impeller (The Rotating Part):
A wheel with backward-curved vanes or blades. It rotates at high speeds, transferring kinetic energy directly to the fluid. Impellers can be:
β’ Closed: Vanes are sandwiched between two discs (most efficient, used for clean water).
β’ Semi-open: Vanes are attached to one disc (used for slightly dirty water).
β’ Open: Vanes are open on both sides (used for slurries and thick liquids).
2. The Casing (The Stationary Part):
An airtight passage surrounding the impeller. It is designed to guide the fluid from the inlet to the outlet and convert kinetic energy (speed) into pressure. The most common type is a Volute Casing (a spiral-shaped casing with a gradually increasing cross-sectional area).
1.
The Suction Pipe (Inlet):
The pipe connected to the center (called the "eye") of the impeller, through which fluid enters the pump.
2.
The Delivery Pipe (Outlet):
The pipe through which the pressurized fluid is discharged. It usually features a control valve to regulate flow.
3.
Shaft and Bearings:
The shaft connects the impeller to the motor. Bearings support the rotating shaft and reduce friction.
4.
Shaft Seal (Stuffing Box/Mechanical Seal):
Prevents liquid from leaking out of the pump casing along the rotating shaft.
ββββββββββ
2. The Working Principle (Step-by-Step)
The working principle of a centrifugal pump is based on centrifugal force. When a body of liquid is rotated by an external force, it is thrown away from the center of rotation, creating pressure.
Here is the step-by-step process of how it operates:
Step 1: Priming
Before starting the pump, the suction pipe and casing must be completely filled with the liquid to be pumped (a process called priming). If there is air inside, the pump cannot create the vacuum needed to lift the liquid because air has a much lower density than water, meaning the centrifugal force generated on air is negligible.
Step 2: Rotation of the Impeller
When the electric motor is turned on, it rotates the impeller at high speed inside the water-filled casing.
Step 3: Generation of Centrifugal Force
As the impeller rotates, the liquid trapped between its vanes is forced to rotate with it. The rotation subjects the liquid to centrifugal force, which flings the liquid radially outward toward the outer edge of the impeller.
Step 4: Vacuum Creation at the "Eye"
Because the liquid is thrown outward, a localized low-pressure zone (vacuum) is created at the center of the impeller (the "eye").