Working Principle of Hydraulic Pumps
Hydraulic pumps convert mechanical energy into hydraulic energy by periodically changing the volume of sealed chambers to achieve oil suction, compression, discharge, and circulation.
1. Suction Stage (Low-Pressure Intake)
- Volume Expansion and Negative Pressure Formation
- Drive Shaft Movement: The drive shaft moves gears, vanes, or pistons, causing the pump chamber volume to increase rapidly.
- Negative Pressure Zone: As the internal chamber pressure drops below the tank pressure (close to atmospheric pressure), a negative pressure zone is formed, drawing oil into the pump chamber.
- Oil Inlet Path
- Inlet Check Valve: Oil enters the pump chamber through an inlet check valve or open channel.
- Specific Pump Actions:
- Gear Pump: The gear disengagement side forms a suction chamber.
- Piston Pump: Pistons retract to draw in oil.
2. Compression Stage (Pressure Increase)
- Volume Reduction and Oil Compression
- Continued Movement of Mechanical Components: The sealed chamber volume gradually decreases, compressing the oil.
- Specific Pump Actions:
- Piston Pump: Cam or swashplate pushes pistons forward.
- Vane Pump: Eccentric rotor compresses the oil chamber.
- Check Valve Flow Control
- Inlet Check Valve Closes: Due to increased pressure, the inlet check valve closes automatically to prevent backflow.
- System Demand Pressure Achieved: Pressure continues to build up to the system demand level (e.g., oil compressed in the gear meshing area).
3. Discharge Stage (High-Pressure Output)
- High-Pressure Oil Delivery
- Outlet Check Valve Opens: Compressed high-pressure oil flows through the outlet check valve or fixed channel into the hydraulic system.
- Discharge Pressure Determinants: Discharge pressure is determined by the pump's structure (such as gear meshing precision, piston stroke) and drive speed.
- Power Transmission
- Actuator Drive: Oil pressure drives actuators (such as cylinders, motors) to perform mechanical actions.
- Specific Pump Characteristics:
- Gear Pump: Continuous discharge but noticeable pulsation.
- Piston Pump: Smooth discharge with adjustable pressure.
4. Unloading Stage (Pressure Release and Recirculation)
- Pressure Equalization and Oil Return
- Residual Pressure Release: After discharge, the pump chamber connects with the oil tank via internal channels or external circuits, releasing residual pressure.
- Oil Returns to Tank: Some systems have return paths allowing oil to flow back to the tank to complete the cycle.
- Sealing Assurance
- Sealing Methods: Gear pumps rely on tooth flank clearance for sealing; vane pumps use vanes contacting the stator to prevent high-pressure oil leakage.
Key Influencing Factors
- Volumetric Efficiency: Depends on the tightness of the sealed chamber; excessive leakage reduces output pressure.
- Drive Method: Electric motors/internal combustion engines provide constant speeds, while manual pumps depend on operator force frequency.
- Oil Properties: High viscosity causes suction difficulties, while low viscosity can lead to internal leakage.
Comparison of Typical Pump Types：
| Type | Suction Action | Discharge Action | Pressure Characteristics |
|---|---|---|---|
| Gear Pump | Gear disengagement side expands for suction | Gear meshing side compresses for discharge | Medium-low pressure, noticeable pulsation |
| Vane Pump | Centrifugal force extends vanes forming suction chamber | Vanes retract, compressing oil chamber for discharge | Medium pressure, uniform flow |
| Piston Pump | Pistons retract to draw in oil | Pistons advance, compressing oil | High pressure, adjustable flow |
