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Demystifying Hydraulic Pump: Types, Selection, and Applications
A hydraulic pump is a mechanical device used in hydraulic systems for converting mechanical power to hydraulic energy. They work by pushing large amounts of hydraulic fluid through a cylinder or motor. Different types of hydraulic pumps are capable of generating different types of liquid pressure.
Hydraulics is a flexible and efficient form of energy transfer. Many modern machines and devices make use of innovative hydraulic pump technology as their source of power.
There are several types of hydraulic pumps that are used in various kinds of equipment and machinery. The three most common types of hydraulic pumps are gear pumps, piston pumps, and vane pumps. However, there are other kinds of pumps as well. They are hydraulic pumps with a clutch, hydraulic pumps with a dump valve, and hydraulic pumps used for refuse vehicles such as dry valve pumps.
In this article, we’ll look into the different types of hydraulic pumps their features, and their applications.
Working principle of hydraulic pumps
The principle of operation of the hydraulic pump is based on the method of displacement which involves the use of mechanically sealed chambers to transport fluid from the inlet or suction port to the outlet or pressure port.
Types of Hydraulic Pumps
There are generally 3 categories of hydraulic pumps – Positive Displacement Pumps, Dynamic Pumps, and Hybrid Pumps.
Positive Displacement Pumps
Positive displacement pumps are a type of hydraulic pump that operates by trapping a fixed amount of fluid and forcing it into the hydraulic system. Positive displacement pumps are known for their ability to maintain a constant flow rate regardless of changes in pressure or viscosity. There are three types of positive displacement pumps:
- Gear pumps,
- Vane pumps, and
- Piston pumps.
Dynamic Pumps
Dynamic pumps are a type of hydraulic pump that operates by imparting kinetic energy to the fluid and then converting that energy into hydraulic energy. Dynamic pumps are known for their high flow rates and low cost, but they are not suitable for applications that require a constant flow rate. There are three types of dynamic pumps:
- Centrifugal pumps,
- Axial flow pumps, and
- Mixed flow pumps.
Hybrid Pumps
Hybrid pumps are a type of hydraulic pump that combines the features of positive displacement and dynamic pumps. Hybrid pumps are known for their high efficiency, high-pressure capability, and variable flow rate. There are two types of hybrid pumps:
- Screw pumps and
- Lobe pumps.
Gear pumps
Gear pumps, the most commonly used type of positive displacement pump, are comprised of two gears rotating in opposite directions. This rotation creates a vacuum, which then pulls fluid into the pump. As the gears continue to rotate, they capture the fluid in the gaps between the teeth and the pump casing and ultimately push it into the hydraulic system. Despite being uncomplicated, dependable, and economical, gear pumps are not optimal for high-pressure applications.
The prevalence of gear pumps within hydraulic systems can be attributed to their simple design and ease of accessibility. These pumps are classified as fixed displacement or positive displacement pumps and only possess a few moving components. Gear pumps have the capability to operate at pressures of up to 210 bar, and their chambers are formed through the movement of the gear wheel and the housing of the hydraulic pump. With each rotation of the pump’s shaft, a consistent volume of flow is produced.
Different types of gear pumps available include:
- External gear pumps
- Internal gear pump
- Screw spindle jump
- Gear ring pump.
Applications: The gear pumps most commonly used in open-center hydraulic systems are the gear pump, the vane pump, and the lobe pump. Gear pumps come in a wide range of sizes. The smaller ones will be used in engine systems with low pressures and low horsepower needs. The larger sizes are used in high-pressure applications.
Vane pumps
Vane pumps are another classification of positive displacement pumps that function through the incarceration of fluid within a rotor and stator. The rotor is composed of vanes that sway in and out of the rotor slots, thus forming compartments that ensnare the fluid and convey it through the pump.
Within the housing, the vane pump contains a cartridge. The input shaft of the pump is annexed to the back of the cartridge while the output shaft is connected to the front. The spinning motion of the input shaft forces oil to be pumped. The greater the rotation of the input shaft, the greater the amount of oil expelled from the pump. In a vane pump, the vanes are situated on the cartridge. Consequently, as the input shaft rotates, the vanes alter the area of the cartridge.
Vane pumps are hydraulic pumps with low-flow pulsations. They are notably noiseless and have lower pressure capabilities. At a hydraulic pressure of 300ba, vane pumps can achieve speeds of up to 3,600rpm.
Vane pumps come in different types:
- Variable displacement
- Fixed displacement
- Single dension vane pump
- Double dension vane pump and
- Triple dension vane pump.
Applications: Vane pumps are known for their smooth operation, low noise level, and high efficiency, but they are more complex and expensive than gear pumps. They have usually used injection molding and die-casting machines applied by several industries as well as land and road construction companies.
Piston pumps
Hydraulic piston pumps are the most intricate kind when it comes to positive displacement pumps. They are made up of a cylinder block, a piston, and a swash plate. The piston moves back and forth within the cylinder block to create a vacuum that pulls fluid into the pump. As the piston moves, it forces the fluid through the pump and into the hydraulic system. High efficiency, high-pressure capacity, and variable flow rate are among the advantages of piston pumps. However, of the three types of positive displacement pumps, they are the most expensive and necessitate the most maintenance.
The use of hydraulic piston pumps is prevalent when it comes to high operating pressures, as they are designed to handle more pressure than gear pumps with the same displacement. To generate suction and flow discharge, reciprocating pistons are used alternately. However, the acquisition cost of this type of pump is higher, and it is typically vulnerable to contamination. There are vane pump designs that can achieve an efficiency of 95 percent. Piston pumps are intended to withstand greater pressure than gear or vane pumps.
There are two types of piston pumps:
- Axial piston pump and
- Radial piston pump.
Applications: Piston pumps are widely used in hydraulic systems where high-pressure and high-flow-rate capabilities are required. They are commonly used in heavy-duty applications such as construction equipment, mining machinery, and oil rigs. Piston pumps are also used in automotive power steering systems and in various industrial applications such as metal forming, plastic injection molding, and food processing. Due to their ability to handle a wide range of viscosities, piston pumps are ideal for applications that require precise flow control, such as chemical processing and metering systems.
Centrifugal pumps
Hydraulic centrifugal pumps work by using the centrifugal force generated by the spinning impeller to push the fluid outwards and into the hydraulic system. The impeller’s rotation creates a low-pressure zone near the center, which draws fluid into the pump through the inlet. The fluid is then accelerated by the impeller’s blades and forced through the pump’s discharge outlet. The pump’s casing or volute helps to convert the kinetic energy of the fluid into pressure energy, which helps move the fluid through the hydraulic system. This process is continuous, and the pump can continue to move fluid as long as it is powered. Overall, hydraulic centrifugal pumps are efficient and effective in many fluid-handling applications due to their straightforward design and operation.
Hydraulic centrifugal pumps can be classified into several categories based on their design, construction, and application. Some of the most common classifications include:
- Single-stage and multi-stage centrifugal pumps,
- Axial-flow and radial-flow centrifugal pumps,
- Self-priming and non-self-priming centrifugal pumps, and
- End-suction and split-case centrifugal pumps.
Applications: Hydraulic centrifugal pumps are highly versatile and widely used across various industries for their reliability and cost-effectiveness. They are used in water supply and irrigation systems to distribute water, industrial processes to move fluids, HVAC systems to circulate fluids, power generation systems for cooling, and marine applications for ballast and cooling systems. Overall, centrifugal pumps are an essential component of many fluid-handling applications due to their efficiency and effectiveness.
Axial flow pumps
Axial flow pumps are another type of dynamic pump that operates by propelling the fluid parallel to the axis of the pump. Axial flow pumps are known for their high flow rate and low head, but they are not suitable for high-pressure applications.
Hydraulic axial flow pumps work by using a rotating propeller-like impeller to draw fluid into the pump and then push it out through the outlet in the same direction as the impeller’s rotation. As the impeller rotates, it propels the fluid parallel to the axis of the pump, creating a flow pattern that gives axial flow pumps their name. The pump’s design ensures that the fluid flows with minimal turbulence, resulting in high flow rates and low head. Axial flow pumps are ideal for applications that require moving large volumes of fluid, such as irrigation, drainage, and flood control systems. They are also commonly used in cooling systems for power generation plants, where large quantities of water need to be circulated to remove heat from the equipment. However, their low-pressure capabilities make them unsuitable for applications that require high-pressure pumpings, such as fire suppression systems or high-pressure water jet cutting.
Hydraulic axial flow pumps can be classified into several categories based on their design, construction, and application. Some of the most common classifications include:
- Propeller and mixed-flow axial flow pumps,
- Fixed-pitch and adjustable-pitch axial flow pumps, and
- Single-stage and multi-stage axial flow pumps.
Applications: Hydraulic axial flow pumps are versatile devices used in various industries for their high flow rate and low head. They are classified based on their design and construction and find applications in irrigation systems, flood control, water treatment, cooling systems, and hydroelectric power generation. Axial flow pumps are commonly used to move large volumes of water from a source to a distribution network, circulate water or other fluids through cooling systems, and generate electricity in hydroelectric power plants.
Mixed flow pumps
Mixed flow pumps are a hybrid of centrifugal and axial flow pumps. They operate by combining the centrifugal force of the impeller with the axial flow of the fluid, resulting in a higher head and flow rate than centrifugal pumps. Mixed flow pumps are suitable for a wide range of applications, including irrigation, water treatment, and HVAC systems.
Screw pump
Screw pumps, which comprise multiple intermeshing screws that rotate in opposite directions, generate chambers that confine and transfer fluid through the pump. These pumps are renowned for their low noise levels, high efficacy, and ability to process fluids with high viscosity. However, compared to other pump variants, screw pumps are intricate and costly.
Screw pumps are categorized as fixed displacement pumps and have two screws that interconnect and are contained within a single compartment. Hydraulic systems aboard ships commonly use these pumps, particularly for high flows at comparatively low pressures. Their purpose is to control ball valves and assist in the operation of steering and other mechanisms. These pumps operate with low sound levels but have suboptimal efficiency levels. Hydraulic transition is usually transmitted in a direction opposite to that of the flow.
Lobe pumps
Lobe pumps are another type of hybrid pump that operates by trapping the fluid between two or more rotating lobes. Lobe pumps are known for their gentle handling of the fluid, high efficiency, and low pulsation, but they are not suitable for high-pressure applications.
Pump Selection
When selecting a hydraulic pump, there are several factors to consider, including flow rate, pressure, viscosity, temperature, and environment. It is important to choose a pump that is designed for the specific application to ensure optimal performance and longevity. Common mistakes to avoid when selecting a hydraulic pump include underestimating the flow rate and pressure requirements, ignoring the fluid viscosity, and not considering environmental factors.
Maintenance and Troubleshooting
Regular maintenance is essential to ensure the optimal performance and longevity of hydraulic pumps. Common maintenance procedures include checking for leaks, replacing worn parts, and changing the fluid and filters. It is also important to troubleshoot any issues with the hydraulic system as soon as possible to prevent further damage.
FAQs
Which is the most efficient hydraulic pump?
A piston pump that works at almost 95% efficiency is widely regarded as the most efficient hydraulic pump. It has high efficiency in converting input mechanical energy into hydraulic energy. The overall efficiency of a hydraulic pump is obtained by multiplying the volumetric efficiency by the mechanical efficiency. A piston pump does on not only deliver a highly efficient pump but also gives off less waste heat
What is a 2-stage hydraulic pump?
A 2-stage hydraulic pump is a hydraulic pump that essentially contains 2 pump sections. It has an internal pressure-sensing valve that cuts over between the two pump sections. One section of the pump helps to generate flow at lower pressure while the other section helps to generate higher pressure at a lower pressure. 2-stage hydraulic pumps are usually employed in log splitters for retracting the piston into the cylinder.
What is the advantage of hydraulic pumps over other types of pumps?
Hydraulics is more advantageous than electric and gas pumps in that they have lower weight and high capabilities. Hydraulic units are generally powered by a significantly smaller motor that weighs less than the motors used in electric machines. Hydraulic pumps usually come with better system designs, modern technological components, and greater augmentation for the energy efficiency of machines. Also, the design of the hydraulic pumps functions in a more energy-efficient manner. This makes them the choice of use in many commercial industries.
Conclusion
Hydraulic pumps are now widely used in different industries to maximize performance, due to their high efficiency. There are several types of hydraulic pumps, with vane pumps, piston pumps, gear pumps, and screw pumps dominating the market. Hydraulic pumps play an integral role in maintaining precision and required force for most systems. Some of their areas of application include the manufacturing of construction equipment, cranes, trucks, tractors, hand tools, and so on.
