# Hydraulic Pump

Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic. A hydraulic pump is a mechanical source of power that converts mechanical power into hydraulic energy ( hydrostatic energy i.e. flow, pressure). This pump generates flow with enough power to overcome the pressure induced by the load at the outlet. When a hydraulic pump operates, it creates a vacuum at the pump inlet, which transports liquid from the reservoir to the pump in the inlet line and by mechanical action drives this liquid to the pump outlet and forces it into the hydraulic system. . Hydrostatic pumps are positive displacement pumpsWhereas hydrodynamic pumps can be fixed displacement pumps, in which the displacement (flow through the pump per rotation of the pump) cannot be adjusted, or variable displacement pumps , which have a more complex construction that allows the displacement to be adjusted. Is. Hydrodynamic pumps are more frequent in day to day life. The different types of hydrostatic pumps all work on the principle of Pascal’s law .

## Hydraulic pump type

### Gear pump

Gear pumps (with external teeth) (fixed displacement) are simple and economical pumps. Gear pumps for hydraulics will have a sweep volume or displacement of approximately 1 to 200 ml. They have the lowest volumetric efficiency ( ) of all three basic pump types (gear, vane and piston pumps) [1]\eta_v \approximately 90 \%These pumps create pressure through the mesh of the gear’s teeth, which forces the fluid around the gear to build up pressure toward the outlet. Some gear pumps can be significantly noisier than other types, but modern gear pumps are highly reliable and more quiet than older models. This is partly due to designs incorporating split gears, helical gear teeth and higher precision/quality tooth profiles that mesh and unmesh more easily, reducing pressure ripple and associated damaging problems. Another positive feature of gear pumps is that catastrophic breakdowns are much less common than with other types of hydraulic pumps. This is because the gears slowly wear out the housing and/or the main bushings,

### Rotary vane pump

A rotary vane pump is a positive-displacement pump consisting of vanes mounted on a rotor that rotates inside a cavity. In some cases these vanes may have variable length and/or may be tensioned to maintain contact with the walls as the pump rotates. An important element in vane pump design is how the vanes are pushed into contact with the pump housing. is, and how the wen tips are mechanized to the point. A variety of “lip” designs are used, and the main purpose is to provide a tight seal between the inside of the housing and the vane, as well as reduce wear and metal-to-metal contact. Forcing the vane out of the rotating center and toward the pump housing is accomplished using spring-loaded vanes, or more traditionally, the vanes are loaded hydrodynamically (by means of pressurized system fluid).

### Screw pump

The screw pump (fixed displacement) consists of two Archimedes’ screws that are interconnected and enclosed within a single chamber. These pumps are used for high flows at relatively low pressures (up to 100 bar (10,000 kPa)). [ clarification needed ] They were used on board ships where a constant pressure hydraulic system extended through the entire ship, particularly for controlling ball valves [ clarification needed ] but also steering gear and other systems. To help you run. The advantage of screw pumps is the low noise level of these pumps; However, the efficiency is not high.

The major problem with screw pumps is that the hydraulic reaction force is transmitted in a direction that is axially opposite to the direction of flow.

There are two ways to solve this problem:

1. Insert a thrust bearing under each rotor;
2. Create hydraulic balance by directing hydraulic force to the piston at the bottom of the rotor.

Types of screw pumps:

1. single end
2. double end
3. single rotor
4. multi rotor timing
5. Multi rotor untimed.

### Bent axis pump

bent axis pump, axial piston pumps and motors using the bent axis principle, fixed or adjustable displacement, exist in two different basic designs. Thoma-principle (engineer Hans Thoma, Germany, patent 1935) with a maximum angle of 25 ° and Wahlmark-principle (Gunnar Axel Wahlmark, patent 1960) driveshaft with piston rod, piston ring and piston in one piece with max. 40 degrees between centerline and piston (Volvo Hydraulics Co.). These have the best efficiency of all the pumps. Although in general, the largest displacement is about one liter per revolution, a two-liter swept volume pump can be made if necessary. Often variable-displacement pumps are used so that the oil flow can be carefully adjusted. These pumps can normally operate in continuous operation with a working pressure of up to 350-420 bar.

### Inline axial piston pump

Using a variety of compensation techniques, the variable displacement types of these pumps meet consistent fluid discharge and load requirements per revolution, maximum pressure cut-off settings, horsepower/ratio control, and even fully electro proportional systems. Depending on the system pressure can change, requiring no other input than electrical signals. This provides potentially immense power savings compared to other constant flow pumps in systems where the prime mover/diesel/electric motor rotation speed is constant and the required fluid flow is not constant.

Radial piston pump is a form of hydraulic pump. Unlike axial piston pumps, the working pistons extend in the radial direction symmetrically around the drive shaft.

## Hydraulic pump, calculation formula

### Flow

{\displaystyle Q=n\cdot V_{\text{stroke}}\cdot \eta _{\text{vol}}}

where

• Q Flow(m3 / s)
• n Stroke Frequency (Hz)
• Vstroke stroke volume ( m3 )
• , volumetric efficiency

### Power

{\displaystyle P={n\cdot V_{\text{stroke}}\cdot \Delta p \over \eta _{\text{mech}}}}



where

• P, power (W)
• n Stroke Frequency (Hz)
• Vstroke stroke volume ( m3 )
• , pressure difference at the pump (Pa)
• Mechanical / hydraulic efficiency

### Mechanical efficiency

{\displaystyle n_{\text{mech}}={T_{\text{theoretical}} \over T_{\text{actual}}}\cdot 100\%}

where

• nmech mechanical pump efficiency percentage
• Ttheoretical theoretical torque to drive
• TActual Actual torque to drive

### Hydraulic efficiency

{\displaystyle n_{hydr}={Q_{real} \over Q_{theoretical}}\cdot 100\%}

where

• nhydr hydraulic pump efficiency
• QTheoretical Theoretical Flow Rate Output
• Qactual actual flow rate output