How does a hydraulic pump work?

How does a hydraulic pump work?

How does a hydraulic pump work?
A hydraulic pump is a mechanical device that converts mechanical power into hydraulic energy. It produces flow of sufficient strength to overcome the pressure caused by the load.

A hydraulic pump performs two functions in operation. First, its mechanical action creates a vacuum at the pump inlet, then allows atmospheric pressure to push the liquid out of the chamber and then pump the liquid into the pump's inlet line. Second, its mechanical action transmits this fluid to the pump outlet and forces it into the hydraulic system.

What are the most common hydraulic pumps?
The three most common hydraulic pump designs are: vane pump, gear pump and radial piston pump. All are well suited for common hydraulic uses, but piston design is recommended for higher pressures.

Most of the pumps used in hydraulic systems are positive displacement pumps. This means that the pumping element replaces (supplies) the same amount of fluid for each return cycle. The distribution per cycle remains nearly constant regardless of changes in pressure.

Positive displacement pumps are grouped into fixed or variable displacement. The output of a fixed displacement pump remains constant during each pumping cycle and at a given pump speed. Changing the geometry of the displacement chamber changes the output of the variable displacement pump.

Fixed displacement pumps (or screw pumps) make very little noise, so they are perfect for use in theaters and opera houses, for example. On the other hand, variable displacement pumps are particularly well suited in circuits where hydraulic motors are used and variable speeds or the ability to reverse are required.

Learn more about Piston Pumps
A piston pump works flawlessly with large flows at high hydraulic system pressures.

Applications that commonly use a piston pump include: marine utility power, machine tools, mobile and construction equipment, metal forming, and oilfield equipment.

As the name suggests, a piston pump works via pistons that move back and forth in cylinders connected to the hydraulic pump. A piston pump also has excellent sealing properties.

A hydraulic piston pump can operate in large volumes thanks to its low oil leakage. Some pistons require valves on the intake and pressure ports, while others require valves on the inlet and outlet channels. Valves (and sealing properties) at the end of reciprocating pumps will further improve performance at higher pressures.

What are the features of the axial piston pump?
The axial piston pump is probably the most widely used variable displacement pump. It is used in everything from heavy industry to mobile applications. Different balancing techniques will continually change the pump's fluid discharge per revolution. Also, change the system pressure according to load requirements, maximum pressure cut-off settings, and ratio control. This means significant power savings.

There are two principles that characterize the axial piston pump. First the swash plate or bent axis design and second the system parameters. System parameters include the decision whether to use the pump in open or closed circuit.

The return line in the closed loop circuit is under constant pressure. This must be taken into account when designing an axial piston pump used in a closed circuit. It is also very important that a variable displacement volume pump is installed and working in addition to the axial piston pump in the systems. Axial piston pumps can alternate between a pump and a motor in some fixed displacement configurations.

How does an inclined axial piston pump work?
Twisted axis pumps are the most efficient of all pumps.

The angle of rotation determines the displacement volume of the bent axis pump. The pistons in the cylinder bore move when the shaft rotates. The swash plate in the swash plate design supports the rotating pistons. Also, the angle of the swash plate decides the piston stroke.

Twisted axis principle, fixed or adjustable displacement, available in two different designs. The first design was the Thoma principle with a maximum angle of 25 degrees, designed by the German engineer Hans Thoma and patented in 1935. The second design is under the name of the Wahlmark principle, named after Gunnar Axel Wahlmark (patent 1960). The latter has spherical shaped pistons in one piece with piston rod and piston rings. Also, a maximum of 40 degrees between the driveshaft centerline and the pistons.

In general, the largest displacements are about one liter per revolution. However, if necessary, a two-liter scavenging pump can be made. Variable displacement pumps are often used to carefully adjust the oil flow. These pumps generally operate in continuous operation with an operating pressure of up to 350–420 bar.