Electric hydraulic pumps are devices that use an electric motor as a power source to drive a hydraulic pump. They convert the mechanical energy of the motor into the pressure energy of hydraulic oil. Through internal mechanical motion, they draw in and compress hydraulic oil, then deliver it to the system’s actuators, such as hydraulic cylinders or hydraulic motors, at a higher pressure. The article explains the working principle, main classifications, and selection considerations of electric hydraulic pumps.
A. Components of a Hydraulic System
Power Supply Unit: It converts mechanical energy to hydraulic energy, typically via a hydraulic pump.
Actuators: Convert hydraulic energy to mechanical energy, including linear and rotary motion devices.
Control and Regulation Devices: Manage system pressure, flow, and direction, including various valves.
Auxiliary Devices: Include oil tanks, filters, and hoses, supporting system operations.
Working Medium: Such as hydraulic oil, the fluid responsible for transmitting energy.
B. Working Principle
The working principle of an electric hydraulic pump is based on the principle of changing sealed volumes, converting the mechanical energy from a power unit, such as an electric motor or internal combustion engine, into hydraulic pressure energy.
Principle of Sealed Volume Change: The hydraulic pump changes the size of the sealed volume to achieve the oil intake and compression process. When the sealed volume increases, a partial vacuum is formed, allowing oil from the tank to enter the sealed volume under atmospheric pressure for oil intake. Conversely, when the sealed volume decreases, the oil filled is pressed out, achieving oil compression. This process continues continuously, converting the mechanical energy input by the power source into the pressure energy of the liquid.
This process involves several key steps:
Start-up Phase: The motor drives the rotor of the hydraulic pump to rotate through a coupling or belt.
Suction Process: As the rotor rotates, the volume of the pump’s suction chamber increases, creating a local vacuum that draws hydraulic oil in.
Compression Process: After the hydraulic oil is drawn in, it is transported to the compression area of the pump as the rotor continues to rotate. In this area, due to the interaction between the rotor and the pump casing, the liquid is compressed, its volume decreases, and the pressure increases.
Discharge Process: When the liquid is compressed to a sufficiently high pressure, it is transported to the discharge port of the pump. At this time, the pressure valve at the discharge port opens, allowing high-pressure liquid to enter the hydraulic system.
Continuous Cycle: The motor continues to operate, and the processes of intake, compression, and discharge of the pump cycle continuously, provide a constant supply of high-pressure liquid to the hydraulic system.
C. Classification Methods
Hydraulic Pumps can be classified according to their working principles as follows:
1. Gear Pumps
Compact, simple, and cost-effective, suitable for applications with moderate cleanliness requirements.
External gear pumps, as the gears rotate, create a vacuum in chamber A as the teeth disengage, gradually increasing the volume and drawing oil from the tank. As the gears rotate, the oil filled in the tooth slots is brought to chamber B, where the teeth mesh, the volume gradually decreases, and the hydraulic oil is expelled. The change in the enclosed volume formed by the teeth and the pump casing completes the function of the pump.
2. Vane Pumps
There are double-acting vane pumps and single-acting vane pumps. These pumps provide a uniform flow rate and smooth operation, suitable for systems that require high working pressure and volumetric efficiency. As the rotor rotates, the vanes, under the action of centrifugal force and pressure oil, press their tips against the inner surface of the stator.
The working volume formed by two vanes, the rotor, and the inner surface of the stator, first increases from small to large for oil intake and then decreases from large to small for oil discharge. As the vanes rotate a full circle, they complete two intakes and two discharges, using the volume change within the vane slots for the pump’s operation.
3. Classification by Flow Control Method
Constant Flow Pumps: The output flow remains stable during operation, unaffected by changes in system pressure.
Variable Flow Pumps: The output flow can be adjusted according to system requirements.
4. Classification by Drive Method
Direct Drive Pumps: The motor is directly connected to the pump shaft, driving the work of the pump.
Indirect Drive Pumps: The motor drives the work through belts, gears, or other transmission devices.
5. Classification by Structural Form
Internal Gear Pumps: Gears or rotors mesh inside the pump.
External Gear Pumps: Gears or rotors mesh outside the pump.
6. Classification by Sealing Method
Mechanical Seal Pumps: Use mechanical seals to prevent liquid leakage.
Packing Seal Pumps: use packing to seal the pump oil.
Each type of electric hydraulic pump has its specific application scenarios and advantages. In practical applications, the selection of the hydraulic pump needs to be based on the specific system requirements and working conditions.
D. Factors to Consider When Selecting an Electric Hydraulic Pump
When selecting an electric hydraulic pump, consider the flow rate, pressure requirements, efficiency, and structural compatibility with the hydraulic system’s installation space and operating conditions. The details are as follows:
1. Flow Rate: The flow rate is the primary consideration when selecting an electric hydraulic pump. It refers to the volume of hydraulic oil delivered by the pump per until of time. Flow rate selection should be based on the actual needs of the hydraulic system.
2. Pressure: It is another important factor in selecting an electric hydraulic pump. It refers to the pressure of the hydraulic oil output by the pump. The selection of pressure should be determined based on the highest working pressure of the hydraulic system. If the highest working pressure of the hydraulic system is low, gear pumps or vane pumps should be selected; if the highest working pressure of the hydraulic system is high, piston pumps should be selected.
3. Efficiency: It is an important indicator when selecting an electric hydraulic pump. It refers to the efficiency with which the pump converts the mechanical energy of the motor into the pressure energy of hydraulic oil. The higher the efficiency of the pump, the lower its energy consumption. When selecting an electric hydraulic pump, it is advisable to choose a pump with high efficiency whenever possible.
4. Structure: The structure of the electric hydraulic pump should be selected based on the installation space of the hydraulic system and the application scenario. For example, if the installation space of the hydraulic system is limited, a compact pump should be selected; if the working environment of the hydraulic system is harsh, a pump with corrosion resistance, dust-proof, and water-proof features should be chosen.
F. Safety Operation Procedures
1. Unauthorized personnel are prohibited from operating the electric hydraulic pump station.
2. Before pressurization, verify the electrical system and grounding are secure. The pressure gauge should be checked for appropriate range and accuracy. check whether the electrical system and grounding are normal. The hydraulic oil must meet the hydraulic test documentation requirements.
3. Pressure increase must be slow, and over-pressure is prohibited. After pressurization, hammering the cylinder or other pieces and connecting pipelines is forbidden. If defects are found in the cylinder and pipeline, the pressure should be lowered to zero before handling, and do not work under pressure.
4. Hydraulic test procedures and steps:
a. Set the relief valve of the hydraulic pump station to the “0” position, start the hydraulic pump station, and adjust the relief valve to increase pressure slowly.
b. Check for leaks in the cylinder and connecting pipelines.
c. Conduct pressure and hold pressure tests according to the requirements of the “Hydraulic Cylinder Hydraulic Test Process Document”.
d. After the pressure test is completed, close the hydraulic pump station, open the return oil discharge valve, and discharge the hydraulic oil in the cylinder and connecting pipelines.
e. Remove the connecting pipelines. Seal the ports of the cylinder, pump station, and pipelines with plastic plugs to prevent dust and impurities from entering.
f. Place the qualified area or unqualified test pieces in their respective designed areas.
g. After the pressure test is completed, it is strictly forbidden to disassemble the connecting pipelines under pressure.
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