Advantages and disadvantages of hydraulic gear pumps

A hydraulic gear pump is a type of rotary pump that creates fluid flow and pressure by rotating two gears inside a housing. A gear is driven by an external power supply; The other is a pinion. The fluid enters through the suction created at an inlet port and is pressurized and moved by the rotation of the gears until it reaches the discharge port.


Hydraulic gear pumps basically consist of the two gears, a housing, end caps and a drive shaft. This is an advantage over the other two types of rotary hydraulic pumps, the type of vanes and the type of piston, which require complex rotating assemblies to pump fluid. With fewer moving parts, the gear pump is less susceptible to damage and wear, and therefore requires less maintenance.

Flow range

The hydraulic gear pump is a fixed positive displacement pump. This means that the flow is controlled by the speed of the rotation of the transmission shaft and therefore requires a variable speed motor to vary the flow. This can be a disadvantage compared to the vane and piston type pumps, in which the drive speed can be constant and the flow can be controlled by the vane regulation or the piston positions.

Types of fluids

A hydraulic gear pump is capable of handling fluids of almost any type and viscosity; This is one of its main advantages. Gear pumps move petroleum products, food, acids, other corrosive liquids, among others. They can handle fluids as thin as a lighter liquid and as thick as asphalt, as thin as acetic acid and as thick as chocolate, and as thin as whiskey and as thick as wood pulp. Vane and piston type pumps have disadvantages in many such uses due to the need for free movement of vanes and pistons. In addition, hydraulic gear pumps are better able to meet the sanitary requirements of the food industry and are easier to maintain.

Vane pump vs. gear pump

Based on the constructive form of the pumps and their design, we can classify the pumps in many different ways, but the most common is the classification into three large groups: Gear Pumps, Vane Pumps and Piston Pumps. In this blog post we are going to talk about the first two groups.

Gear Pumps

Gear pumps are compact, relatively inexpensive and have few moving parts. External gear pumps consist of two gears, generally of the same size, that engage each other inside a housing. The drive gear is an extension of the drive shaft. When it spins, it drags the second gear. When both gears rotate, they cause a partial vacuum in the inlet chamber and the fluid is introduced to the pump through the inlet port.

This fluid is trapped between the housing and the rotation teeth of the gears, moves around the housing and is pushed through the outlet hole. The pump generates flow and pressure, so that it transfers energy from the input source, which is mechanical, to a hydraulic power actuator. With the same principle of operation are internal gear pumps, lobe pumps and gerator pumps. The following figure shows the constructive form of this class of pumps.

Vane pumps

They are built by a circular section housing, with a ring fitted inside. A grooved rotor rotates eccentrically within this ring, in whose grooves a vane is housed that can move radially.

The rotor is connected to an electric motor by means of a shaft. When the rotor rotates, the vanes remain supported against the ring surface, since they tend to come out thanks to the centrifugal force and the pressure applied on the inside of them thanks to springs, forming a positive seal. The fluid enters the pump and fills the large volume area formed by the offset rotor. When the vanes push the fluid around the cam, the volume decreases and the fluid is pushed out through the outlet hole.

To understand the operation of this type of pumps during admission, the eccentricity must be used. Thanks to the eccentricity, an area is generated, using the vanes and the housing, which acts as a hermetic seal that prevents the oil from receding during pump operation. From that zone and product of the centrifugal force, the vanes leave the grooves of the rotor, adjusting to the inner surface of the ring, thus between each pair of vanes chambers are created that increase the volume and decrease the pressure, so that it is possible to ensure the continuous supply of oil. The oil is taken from these chambers and transferred to the discharge zone.