What is a hydraulic pump? What is its principle? What is its structure? How is it classified?

What is a hydraulic pump? What is its principle? What is its structure? How is it classified?

Today, Anhui Shengshi Datang Chemical Equipment Co., Ltd. is here to provide an interpretation for everyone. A hydraulic pump is the power component of a hydraulic system. It is driven by an engine or motor, draws oil from the hydraulic tank, forms pressurized oil, and discharges it to the actuators. Hydraulic pumps are classified by structure into gear pumps, piston pumps, vane pumps, and screw pumps.

I. Working Principle of Hydraulic Pumps

The working principle of a hydraulic pump is that motion causes changes in the volume of the pump chamber, thereby compressing the fluid to give it pressure energy. The essential condition is that the pump chamber must have a sealed volume change.

A hydraulic pump is a type of pump that provides pressurized fluid for hydraulic transmission. Its function is to convert the mechanical energy of a power source (such as an electric motor or internal combustion engine) into the pressure energy of a liquid. Its cam is rotated by an electric motor. When the cam pushes the piston upward, the sealed volume formed by the piston and the cylinder decreases, forcing the oil out of the sealed volume and discharging it through a check valve to where it is needed. When the cam rotates to the descending part of the curve, the spring forces the piston downward, creating a certain vacuum. The oil in the tank enters the sealed volume under atmospheric pressure. As the cam continuously moves the piston up and down, the sealed volume periodically decreases and increases, allowing the pump to continuously suck in and discharge oil.

Many factors affect the service life of a hydraulic pump. In addition to the pump's own design and manufacturing factors, the selection of components related to the pump's use (such as couplings, oil filters, etc.) and the operation during trial runs also play a role.

II. Components of a Hydraulic Pump

A hydraulic pump consists of three parts: a coupling, a hydraulic tank, and an oil filter.

 1.Coupling:

The drive shaft of a hydraulic pump cannot withstand radial or axial forces. Therefore, it is not allowed to directly install pulleys, gears, or sprockets on the shaft end. Typically, a coupling is used to connect the drive shaft and the pump transmission shaft. If, due to manufacturing reasons, the coaxiality between the pump and the coupling exceeds the standard and there is an assembly deviation, the centrifugal force increases as the pump speed rises, deforming the coupling. The deformation, in turn, increases the centrifugal force, creating a vicious cycle. This results in vibration and noise, thereby affecting the pump's service life. Other influencing factors include loose coupling pins not being tightened in time and worn rubber rings not being replaced promptly.

 2.Hydraulic Tank:

The main functions of the hydraulic tank in a hydraulic system are to store oil, dissipate heat, separate air from the oil, and eliminate foam. When selecting a tank, its capacity must first be considered. Generally, mobile equipment requires 2–3 times the maximum flow rate of the pump, while stationary equipment requires 3–4 times. Next, the oil level of the tank must be considered. When all hydraulic cylinders of the system are extended, the oil level in the tank must not fall below the minimum level. When the cylinders retract, the oil level must not exceed the maximum level. Finally, the structure of the tank must be considered. The partition plates in traditional tanks do not serve to settle dirt. A vertical partition plate should be installed along the longitudinal axis of the tank. A gap should be left between one end of this partition plate and the tank end plate to connect the spaces on both sides of the partition. The inlet and outlet ports of the hydraulic pump should be arranged on the disconnected side of the partition plate, ensuring the farthest distance between the inlet and return oil ports. This allows the hydraulic tank to play a greater role in heat dissipation.

 3.Oil Filter:

Generally, contaminants with a particle size below 10μm have a negligible impact on the pump, while those larger than 10μm, especially above 40μm, significantly affect the pump's service life. Solid contaminant particles in hydraulic oil can easily accelerate the wear of the relative moving parts inside the pump. Therefore, an oil filter must be installed to reduce the degree of oil contamination. The required filtration accuracy is 10–15μm for axial piston pumps, 25μm for vane pumps, and 40μm for gear pumps. This can control the contamination wear of the pump within acceptable limits. Currently, high-precision oil filters are increasingly used, greatly extending the service life of hydraulic pumps.

III. Classification of Hydraulic Pumps

Common types of hydraulic pumps:

 1.Based on whether the flow rate can be adjusted, they are classified into variable pumps and fixed pumps. Those whose output flow rate can be adjusted as needed are called variable pumps, while those whose flow rate cannot be adjusted are called fixed pumps.

 2.Based on the structure commonly used in hydraulic systems, they are classified into three types: gear pumps, vane pumps, and piston pumps.

  a.Gear Pump: Compact size, relatively simple structure, less stringent requirements for oil cleanliness, and relatively low cost. However, the pump shaft is subjected to unbalanced forces, resulting in severe wear and significant leakage.

  b.Vane Pump: Divided into double-acting vane pumps and single-acting vane pumps. These pumps provide uniform flow, smooth operation, low noise, higher operating pressure, and volumetric efficiency compared to gear pumps. However, their structure is more complex than that of gear pumps.

  c.Piston Pump: High volumetric efficiency, minimal leakage, capable of operating under high pressure, and mostly used in high-power hydraulic systems. However, they have a complex structure, require high-quality materials and machining precision, are expensive, and demand high oil cleanliness.

Generally, piston pumps are used only when gear pumps and vane pumps cannot meet the requirements. There are other forms of hydraulic pumps, such as screw pumps, but they are less commonly used compared to the three types mentioned above.