We know that most of the hydraulic applications use hydraulic pumps for converting mechanical energy to hydraulic energy. Both mobile and industrial hydraulic machinery uses hydraulic pumps. Forestry equipment, construction equipment, mining machinery, excavators, dump trucks, cranes, graders, loaders, vacuum trucks, tractors, etc.. use hydraulic pumps to maximize performance. Hydraulic pumps play an integral role in maintaining the precision and efficiency of the entire system.

Plastics, synthetic rubbers, and steel alloys are used as a material for fabrication. The fabricating materials are selected depending on the exposed temperature and pressure of these pumps. Titanium alloys and polymers are high strength materials used for high-pressure applications. The fire resistance and corrosion free properties of hydraulic system paved a way for continued growth in the industry.

In the previous article “Hydraulic Pumps the Ultimate Guide for Beginners” we have discussed all basic details like the introduction, working principle of hydraulic pumps, selection criteria, the difference between hydraulic pumps and motors, etc. In this article, you can learn details on hydraulic pump types and working principle.

Hydraulic Pump Working

The principle behind the working of all pumps is similar. They operate based on the displacement principle. In the previous article, we discussed that the vacuum created at the inlet of the pump will push atmospheric pressure into the pump inlet. Then, this fluid is transferred to the outlet of the pump using mechanical power.

A hydraulic pump contains two check valves, one at the inlet and another one at the outlet. The first check valve allows fluid to enter only through it and the second one allows fluid to discharge through it.

When the piston is pulled,  a vacuum is created inside the cylinder. The vacuum created will close the outlet check valve and atmospheric pressure will push fluid through the inlet valve. When the cylinder is partially filled, the piston is pushed and the fluid molecules will come closer to each other. This will close the inlet valve and opens the outlet valve. The fluid will flow towards the hydraulic system through it. 

Also  Read: How Hydraulic Pump Work

Hydraulic Pump Types

Hydraulic pumps are manufactured to satisfy specific system requirements like temperature, pressure, and type of drive. They are primarily categorized into three:

Hydraulic Gear Pumps

Straight spur, helical, or herringbone gears are used in these pumps. Straight spur gears are commonly used and helical or herringbone gears are much expensive and run quietly. 

In gear pumps, the fluid is carried in between the two meshing gears. A shaft is used to drive the one gear and turns the other one idle. The pump housing and side plates will enclose the chambers formed between the gears.

Gear pumps can withstand pressure around 210 bar and will work at a high speed of 3000-6000 rpm. External gear pumps, internal gear pumps, screw pumps, and ring pump are the different classifications of gear pumps.

External Gear Pumps

Both industrial and mobile systems utilize these pumps for various applications as lubricating pumps in machine tools, fluid power transfer units and oil pumps in engines. Here, to interlock the teeth of gear pumps, one wheel is connected with the drive and another one will rotate in the opposite direction. Bearing block will help to position the wheels for a minimum clearance during teeth interlock. A lobe pump is a type of external gear pump that operates both lobes using drives situated outside the chamber. 

Internal Gear Pumps

Internal gear pumps are versatile and can handle thick hydraulic fluids like asphalt, chocolate, and adhesives. They are used for applications like plastics and machine tools, presses, electric fork-lift, etc. These pumps can handle high viscosity and temperature ranges. Internal gear pumps can operate dry for short periods and are self-priming, non-pulsating and bi-directional. These gear pumps are reliable, easy to maintain and operate because of minimum moving parts. 

Screw Pumps

These pumps are commonly used in theaters and opera houses because of low operating noise. Among the gear pumps, screw pumps have high displacement volume. These pumps contain two or three worm gears inside the pump housing. So, they are also called worm gear pumps. Single-screw, two-screw, and three-screw are the three classifications of screw pumps. These pumps have axial flow in the direction of the power rotor and the fluids will flow linearly.

Ring Pump

These pumps are commonly used in hydraulic power steering systems as a pressure lubrication system. The rotor of the ring pump is directly built inside the housing of a high-pressure pump like a radial piston pump.

Hydraulic Vane Pumps

Vane pumps will operate efficiently on low viscous fluids such as ammonia, solvents, alcohol, fuel oils, gasoline, and refrigerants. The absence of metal to metal contact inside these pumps will eliminate wear associated with it. They have properties like low noise, dry priming, ease of maintenance, and good suction characteristics. Vane pumps provide constant flow by maintaining a high speed up to 3000rpm. 

The operating pressure doesn’t exceed more than 180-210 bar. Some vane pumps with constant pressure or constant power can adjust the center of the vane body. Sliding vane (left), flexible vane, swinging vane, rolling vane, and external vane are different types of vane pumps.  Among these, external vane pumps can handle large solids and flexible vane pumps can handle small solids but they create a good vacuum. For short periods of time, sliding vane pumps can operate dry.

 In unbalanced vane pumps, all pumping action occurs at one side of the rotor and shaft. Unbalanced vane pumps have circular casing and balanced vane pumps have an elliptical casing with different pumping areas on both side of the rotor. Balanced vane pump uses fixed displacement design whereas, unbalanced uses both fixed and variable. 

Hydraulic Piston Pumps

This is a rotary unit that produces fluid flow using the principle of a reciprocating pump. These types of pumps use a combination of many piston-cylinder combinations. Piston pumps can maintain a large fluid flow at high temperature. Efficiency, reliability and compact size are the features of hydraulic piston pumps. These pumps control fluid leakages through efficient sealing practices. Axial-piston pumps and radial piston pumps are the two classifications of the piston pumps. In axial piston pumps, the rotary motion is converted into axial reciprocating motion. In the case of a radial piston pump, the pistons are arranged radially.