What Is a Hydraulic Pump?
Hydraulic pumps generate mechanical energy by operating an electric motor. When a hydraulic pump is driven, oil circulates and converts mechanical energy into fluid energy. Fluid energy is sometimes referred to as hydraulic energy. This fluid energy combines the pressure and flow required by the hydraulic actuator. The pressure would only push the fluid if either of these energies were not being generated. When oil enters the hydraulic actuator, fluid energy is converted to mechanical energy. The converted mechanical energy becomes linear or rotational motion that powers the pump.
Types of hydraulic pumps include general positive displacement pumps, constant displacement pumps, and variable displacement pumps.
Uses of Hydraulic Pumps
Structural products that use hydraulic pressure use a series of operating mechanisms called hydraulic units, which vary slightly in construction type, but all of them have hydraulic pumps built in. Since hydraulic power is a combination of pressure and flow rate, doubling the pressure without changing the flow rate doubles the horsepower. Changing the flow rate by a factor of 2 without changing the pressure will also approximately double the horsepower.
In general, hydraulic pressure is used in many situations where large external power is required, especially in heavy equipment such as excavators and cranes used at construction sites. It is also often used in equipment that is small but requires large torque. For example, they are widely applied in the transportation industry represented by airplanes, ships, and automobiles.
Other pumps that utilize natural forces also exist. A specific example is the use of devices that pump water on farms. Such pumps are used in conjunction with sensors that detect water levels, as they require continuous operation. Windmills are another example. Windmills use hydraulic pumps to pump water out of the ground with the force of the wind.
How to select Hydraulic Pumps
Two types of power use fluids: pneumatic and hydraulic. Both are structured to convert a small force into a large force by applying Pascal’s principle. However, their features are somewhat different.
The pneumatic type is inexpensive and has a simple structure. It is more dependent on the environment, such as ambient temperature, and has lower responsiveness. However, if the appropriate type of hydraulic oil is selected, it can be used in all weather conditions. When large forces that cannot be achieved with the pneumatic type are required, it is advisable to select a hydraulic-type unit and appropriate hydraulic pumps to accompany it.
Principles of Hydraulic Pumps
All pumps are available in positive displacement and non-positive displacement types. Since most hydraulic systems use positive displacement pumps, the principle of positive displacement pumps is discussed here.
A positive displacement pump is divided into two parts: one filled with hydraulic fluid and the other, called a positive displacement chamber, which contains only gas. In a positive displacement pump, an intake valve draws fluid into the pump chamber and an exhaust valve discharges the fluid.
First, when an external driving force is applied to cause piston motion, a negative pressure is generated on the volume chamber side, resulting in suction pressure. This is called the expansion process.
Next, the suction process begins. When this pressure exceeds a certain value, the difference in atmospheric pressure between the hydraulic oil chamber and the oil tank to which it is connected causes the hydraulic oil to be sucked in through the intake valve. At this time, the exhaust valve is closed.
The pressure difference is reversed when the volume chamber side becomes positive pressure. This process is called the compression process.
Finally, the discharge process takes place. Oil is discharged from the exhaust valve by the force of the hydraulic oil being pushed outward. When the oil is pushed out, the intake valve closes and the exhaust valve is released.
These four processes are repeated indefinitely as one cycle to keep pumping the hydraulic oil in a constant direction.
The suction and discharge sides of the oil tank are each equipped with a check valve in one direction, so that when pressure is generated on either side, one side is pulled closed by the pressure and there is no backflow.
Structure of Hydraulic Pumps
Hydraulic systems, including hydraulic pumps, are widely used in industry because they provide large power with little power. First, the system is powered by a prime mover that boosts hydraulic oil pressure via hydraulic pumps. Next, hydraulic oil is fed to the hydraulic actuators by controlling the pressure with hydraulic valves. It is then converted into mechanical energy such as rotational motion. Among these, the hydraulic pumps are the most important equipment to ensure the necessary mechanical power by boosting the pressure of the hydraulic oil.
Hydraulic pumps are mainly divided into “gear type,” “vane type,” and “plunger type”.
Gear pumps boost hydraulic oil pressure by meshing gears in the casing.
Vane pumps have a rotor built into the vane inside the casing, which rotates the vane to raise the pressure of the hydraulic oil. These blades are called vanes.
In a plunger pump, a reciprocating piston or plunger adds pressure to the hydraulic oil to boost pressure.
Both pumps still boost the pressure of the hydraulic oil, but if a leak of hydraulic oil occurs, it contaminates the environment and is time-consuming to deal with. Sealing performance is of a high standard due to advances in technology. However, since leakage will never be zero, installed pump units must be installed inside an oil embankment, for example. In addition, transportable pump units must have good sealing to prevent leakage since the entire unit will be moved. Even if hydraulic oil should leak outside, an oil tank or similar facility can be installed to prevent oil leakage.
Power for Hydraulic Pumps
There are two types of hydraulic pumps: electric and manual. The electric type is mainly used in industry and experimental facilities, and the pump is powered by electricity. On the other hand, the manual type is powered by the force applied by a person. Mainly, the manual type uses a piston in the path to generate power. Hydraulic fluid is pumped into the piston by operating the handle with human power. The piston, under the pressure of the hydraulic fluid, provides power to the outside world. The advantage of using a manual type is that the mechanism is simple and easy to maintain. In addition, the slow transmission of force when transmitting power allows for fine adjustments. This results in risk assessment.
A commonly used hydraulic jack is the hydraulic jack used to change a car tire. This is a manually operated hydraulic pump that transmits power by sending hydraulic oil to the power to lift the car.
The electric type is mostly used in industrial applications, as this pump is used when a greater workload needs to be given. The electric type is more complex in structure than the manual type, so a wide variety of types are prepared according to the performance required. However, pumps with simple structures are also manufactured, making them inexpensive and easy to install. They can also be used on land or water where large amounts of power are required.
Thus, the electric and manual types differ not only in the power source but also in the scale of the application for which they are used.