Hydraulic Pump: Types, Working Principle & Flow Rate
Hydraulic Pump: Types, Working Principle & Flow Rate
What Is a Hydraulic Pump?
A hydraulic pump is a hydraulic component that converts mechanical energy into hydraulic energy. It draws hydraulic oil from a reservoir and transfers it into the hydraulic circuit at a specific flow rate and pressure. The mechanical energy required to drive the pump is typically supplied by an electric motor or an internal combustion engine.
Hydraulic pumps convert mechanical energy into hydraulic energy by creating fluid flow. Pressure is generated when the flow produced by the pump encounters resistance within the hydraulic system. Therefore, the hydraulic pump must provide sufficient flow and pressure to meet the requirements of the components and functions connected to the hydraulic circuit, including combined operations.
Hydraulic pumps are available in different designs and configurations. The most common types of hydraulic pumpsinclude:
- Gear pumps
- Vane pumps
- Piston pumps
Gear pumps transfer hydraulic fluid through the rotation of meshing gears. Vane pumps use vanes mounted in a rotor to move hydraulic fluid from the inlet to the outlet. Piston pumps use reciprocating pistons to draw in and discharge hydraulic fluid.
Hydraulic pumps are widely used in industrial machinery, construction equipment, agricultural machinery, material handling equipment, automotive systems, hydraulic presses, power steering systems, and mobile hydraulic applications.
What Is Hydraulic Pump Displacement and Delivery Volume?
Hydraulic pump delivery volume refers to the amount of hydraulic fluid that a pump can deliver over a specific period of time. In hydraulic systems, this is generally expressed as flow rate, such as liters per minute (L/min) or gallons per minute (GPM).
Pump flow rate depends on several factors, including pump displacement, rotational speed, pump efficiency, and operating conditions.
Hydraulic pump displacement refers to the theoretical volume of fluid displaced by the pump during one revolution. When pump displacement and rotational speed are known, the theoretical flow rate can be calculated.
The relationship between displacement and flow rate is important when selecting a hydraulic pump because the pump must provide the required flow for the desired actuator speed and system performance.
What Are the Main Types of Hydraulic Pumps?
There are three major types of hydraulic pumps commonly used in hydraulic systems: gear pumps, vane pumps, and piston pumps.
- Gear Pumps
Gear pumps are among the most widely used hydraulic pumps because of their simple construction, reliability, and relatively low cost.
During operation, hydraulic oil enters the pump through the suction port. Rotating gears carry the hydraulic fluid through the spaces between the gear teeth and the pump housing from the inlet side to the outlet side. The meshing gears prevent the fluid from flowing directly back toward the inlet, allowing the pump to transfer hydraulic oil and generate flow.
Gear Pump Types
Common gear pump designs include:
- External gear pumps
- Internal gear pumps
- Screw pumps
Gear pumps are frequently used in industrial equipment, agricultural machinery, construction equipment, lubrication systems, and mobile hydraulic systems.
- Vane Pumps
Vane pumps use vanes mounted around a rotating rotor to transfer hydraulic fluid.
The rotor is positioned inside the pump housing, and the vanes move in and out as the rotor rotates. Because the rotor is generally positioned eccentrically within the housing, the volume between the vanes changes during rotation.
As the volume increases, hydraulic oil is drawn into the pump through the inlet port. As the volume decreases, the hydraulic fluid is pushed toward the outlet port.
Vane Pump Types
Vane pumps are generally available in:
- Fixed-displacement vane pumps
- Variable-displacement vane pumps
Vane pumps are commonly selected for applications requiring relatively smooth and consistent hydraulic flow.
- Piston Pumps
Piston pumps use pistons arranged around or along a rotating shaft to draw hydraulic fluid from the reservoir and deliver it to the hydraulic circuit.
As the pump shaft rotates, the pistons move according to the design of the pump. In axial piston pumps, piston movement is controlled by a swash plate or angled plate. In radial piston pumps, the pistons are arranged radially around the drive shaft or cylinder block.
When a piston moves through the suction portion of the pump cycle, hydraulic oil enters the pumping chamber. As the piston moves through the discharge portion of the cycle, the oil is compressed and delivered to the hydraulic circuit.
Piston Pump Types
The two main piston pump configurations are:
- Radial piston pumps
- Axial piston pumps
Piston pumps are widely used in high-pressure hydraulic systems, including industrial machinery, injection molding machines, construction equipment, mobile hydraulics, hydraulic presses, and other demanding applications.
What Is the Working Principle of a Hydraulic Pump?
The working principle of a hydraulic pump is based on positive displacement.
The pump creates a low-pressure area at the suction port, allowing atmospheric pressure or reservoir pressure to push hydraulic fluid into the pump. The pump then mechanically transports a defined volume of hydraulic fluid toward the discharge port.
The hydraulic pump itself primarily creates fluid flow rather than pressure. Pressure develops when the flow encounters resistance within the hydraulic circuit.
For example, when a hydraulic pump supplies fluid to a hydraulic cylinder and the cylinder encounters a load, resistance to the fluid flow causes system pressure to increase.
This makes the hydraulic pump the primary source of hydraulic power transmission within the circuit.
Hydraulic Pump Flow Rate and Power
The flow rate of a hydraulic pump is related to the cross-sectional area through which the fluid moves and the fluid velocity.
If the cross-sectional area is represented by A and the fluid velocity by v, volumetric flow rate can be expressed as:
Q = A × v
Where:
- Q = volumetric flow rate
- A = cross-sectional area
- v = fluid velocity
The force applied to the hydraulic fluid can be expressed as:
F = p × A
Where:
- F = force
- p = hydraulic pressure
- A = cross-sectional area
Hydraulic power can therefore be expressed as:
P = F × v
Combining these relationships gives the commonly used hydraulic power relationship:
P = p × Q
In practical hydraulic systems, pump efficiency must also be considered when determining the required input power.
How to Select a Hydraulic Pump
Selecting the correct hydraulic pump is critical for achieving the required performance, efficiency, reliability, and service life of a hydraulic system.
The pump should be selected according to the application requirements, operating pressure, required flow rate, drive speed, hydraulic fluid, temperature, and installation conditions.
Important factors to consider when choosing a hydraulic pump include:
- Hydraulic fluid properties
- Required working pressure
- Required flow rate
- Pump displacement
- Rotational speed
- Operating temperature range
- Pump drive method
- Maintenance requirements
- Expected service life
- Pump dimensions and installation requirements
- Initial and operating costs
- Advantages and disadvantages of the selected pump design
- Required flow direction
- System duty cycle
- Noise and efficiency requirements
The correct pump should provide the required flow and pressure without being unnecessarily oversized. Proper sizing can help improve system efficiency, reduce energy consumption, and increase component service life.
What Is Hydraulic Pump Flow Rate?
Hydraulic pump flow rate is the volume of hydraulic fluid delivered by the pump per unit of time. It is one of the most important parameters when designing and selecting a hydraulic system.
Flow rate is commonly expressed in:
- Liters per minute (L/min)
- Gallons per minute (GPM)
- Cubic meters per hour (m³/h)
Hydraulic flow rate directly affects actuator speed. For example, increasing the flow supplied to a hydraulic cylinder generally increases the cylinder's extension or retraction speed, assuming other operating conditions remain constant.
Flow rate is determined by factors such as pump displacement, rotational speed, volumetric efficiency, and operating conditions.
For a hydraulic system operating with the same volumetric flow rate, the relationship between flow area and fluid velocity can be expressed as:
Q = A₁ × v₁ = A₂ × v₂ = ... = Aₙ × vₙ
This means that when the flow rate remains constant, fluid velocity changes inversely with the cross-sectional area.
When the available flow area decreases, fluid velocity increases. When the flow area increases, fluid velocity decreases.
Why Is Hydraulic Pump Selection Important?
A hydraulic pump is one of the most important components in a hydraulic power system. Incorrect pump selection can lead to insufficient actuator speed, excessive pressure, energy losses, overheating, premature component wear, or unreliable system operation.
For this reason, hydraulic pump selection and sizing should be based on the actual operating requirements of the hydraulic circuit.
The required flow rate should be calculated according to the desired actuator speed, while the required pressure should be determined according to the force or torque requirements of the application.
When more than one hydraulic pump is used in a hydraulic system, the pumps may be designed to operate simultaneously or according to a specific sequence, depending on the system architecture.
A properly selected hydraulic pump provides the hydraulic circuit with the required flow, pressure, and power, helping the system operate efficiently, reliably, and safely.