All You Need To Know About Gear Pumps And Their Types

A pump is equipment used to take fluid from one place to another from lower to higher position. 

The gear pump is a type of hydraulic pump. It is used to develop high pressure and is also called a fixed displacement pump because it removes the limited quantity of fluid during the rotation of the shaft. PTO gear pumps are one of the best gear pumps, which are also known as Power take-offs gear pumps.

Since gear pumps are positive displacement pumps, you cannot use them without safety devices. If a pump has two sides that are in and out, more pressure will be created in the side of out then it can lead to the burst of pump or rupture of the pump due to its constant working load. It is necessary to use a safety relief valve to not lead to any damage in the pump area.

The first thing when we think about the gear pumps comes to our mind about the gears. The gears used can be of three types as Helical gear, Spur gear, and Herringbone gear. These are the different designs. The most expensive among gear pumps are PTO gear pumps.

These gear pumps use two different gears. One is driven gear and driving gear. If it starts rotating, the pressure will be created at the pump's inlet, and it will get into the pump, and the fixed volume of liquid will be pressurized. 

The cavities between the teeth of the rotating gears so that particular fluid will be pressurized. Delivers from the outlet through the discharge pipe. Works on close tolerances. 

To generate the higher pressure, if there are no tolerances between two gears, we won't generate the required pressure at the pump's outlet. So there is a need to maintain the closed tolerances between the gear pumps.

Types of gear pumps

● External gear pump 

● Internal gear pump.

External gear pumps and their working

External gear pumps are frequently used in large industries. At the inlet of the external gear pump, which is continuously meshing with each other at the inlet side, they come out of the meshing, and the expanded volume gets created at the inlet side of the pump.

Due to the expanded volume, the liquid enters the pump, and suction will get created. The pressure difference will get created over the sides. The liquid will move from the teeth side of the pump, and it will move alongside the casing. 

As the gears continue to rotate against the pump casing, the liquid gets forcefully pressurized at the pump's outlet. So, the trapped fluid will move around the casing from the inlet to the outlet, which will ultimately increase the pressure in the fluid. 

At the discharge side, the two gears will again interlock with each other than the expanded volume that we will be getting at the inlet side, and on the opposite side, the volume will get reduced.

 And due to that reduction in volume, the fluid will then be pressurized then the fluid will be forcefully pushed out of the casing from the discharge pipe. Ultimately you will be getting the pressure at the discharge side also.

Due to the continuously rotating action of the gears, the fluid will get entrapped into the casing, and it will move against the casing, so this will also increase the pressure in the fluid itself, and the liquid is thrown out with a higher velocity and higher pressure. 

Once the fluid is transferred from the suction side to the discharge side, the fluid cannot go back to the suction side. So, all these functions make this type of pump a positive displacement type pump.

Internal gear pumps and their working

Internal gear pumps are specialized arrangements of the gear. They work on the same principle as that of the external gear pump, but it has a different design from external gear.

In the internal gear pump case, the two different gears are the internal gear that is the driven gear. This particular internal gear will have the teeth projecting inside the second gear. 

The driven gear, that particular driven gear, is like continuously meshing with the internal gear. That particular, driven gear is placed eccentrically, and a void is created. To avoid that particular void, a spacer is used. The spacer is fitted in the internal gear pump. 

The primary function of this spacer is to reduce the area to occupy that space and increase the pressure in the fluid to maintain a close tolerance. In any of the gear pumps, the close tolerances are always essential to create a pressurized fluid.

As the internal gear pump starts rotating, the gears will come out of the machine, creating the expanded volume. The pressure difference gets created; the liquid will flow inside the internal gear pump. 

The liquid is forcefully rotated between the meshing of the gear and between the spacer. There is a small clearance between the gear and the spacer so that the liquid will flow from the cavities in the clearance. 

Then the liquid is forcefully thrown out of the discharge outlet. So on the discharge side, the gears will interlock with each other, and the area will get reduced.

Features of the gear pump

● The gear pump has a compact and simple design.

● It has fewer moving parts.

● The pressure developed in the gear pump is less than that of the reciprocating pump but more than a centrifugal pump.

● The flow rate will be less than that of the centrifugal pump but more than the reciprocating pump.

● It can create a pressure of upto 210 bars that is equivalent to 3000 psi.

● The material of the construction used in the gear pump is cast iron or else stainless steel.

● It is also suitable for corrosive liquids like sulphuric acid, sodium hydrochloride, ferric chloride, and sodium hydroxide.

Conclusion

Gear pumps are positive displacement type pumps. They are of two types that work according to the aggressiveness of the liquid. The gear pump is mainly suited for aggressive liquids and also for liquids with higher viscosities.