Introduction

The gear pump was invented by Johannes Kepler in around 1600. Gear pump is considered as one of the most important type of pump among all hydraulic fluid transfer pumps. These types of pumps use gear mechanism for transportation of fluids. Gear pumps fall under the category of positive displacement pumps (rotatory pumps). In general gear pump encloses a fixed volume of fluid by the help of interlocking cogs or by meshing of gears and applies mechanical force/pressure energy on that entrapped volume. The pumping action is a continuous cyclic process which helps to transport the fluid which makes it a non-pulsating or pulse-free flow pump. Even though the pump is considered to be high pressure pump, its size is relatively small compared to other hydraulic pumps. It is used to enhance the pressure of the fluid from inlet to outlet. The outlet pressure in gear pump is further increases by providing casing .

Parts of a Gear Pump


Driver Gear
The driver gear is connected to the prime mover. It rotates using power from the prime mover.

Driven Gear or Idle Gear
The driven gear is forged with the drive gear, and the driver rotates the gear.

Casing
Both the driver gear & the driven gear are packed inside the casing of the gear pumps. It prevents the splashing of the fluid to the surroundings and helps to discharge the fluid. Casing plays an important as the clearance between the teeth of the gears and casing wall decides the discharge pressure. Clearnce may be of the order of 10 microns.It also acts as a safeguard in the case of an accident.

Inlet or suction Side
This is the section in the gear pump through which fluid enters the gear pump. The low-pressure liquid enters the pump from the inlet section.

Outlet or Discharge Side
This is the section in the gear pump through which pressurized fluid is transported to the required area. High-pressure liquid flows from the pump to the outlet section.

Prime Mover
In gear pumps, prime movers are used to providing power to the shaft in which the driver gear is mounted. It can be an electrical motor or an I.C. engine, or it can be manual labor

Safety Valve
A safety valve or release valves are installed on the discharge side so that the pump can be protected from being damaged if additional pressure arises when it is released.

Working of a Gear Pump:


A gear pump belongs to the positive displacement pump category with a continuous delivery rotary pump. At the inlet side a zero suction is created by converting mechanical energy into fluid energy with the help of gear meshings. The space between the gear meshing, carries viscous liquids towards the surface of the wall and which is then pushed to the outlet. Gear pumps are commonly used for pumping high viscosity fluids such as oil, paints, resins or foodstuffs. They are preferred in any application where accurate dosing or high pressure output is required.

As shown in Fig. 3, Gear pump functions in three steps to pump viscous liquid which are described as follows:

1. As the gear rotate in opposite direction, a separation of liquid takes place at the inlet port of the pump
   
2. The separation of liquid creates voids and suction which gets filled by liquid
   
3. With help of rotating mechanism of gears, only displacement of liquid takes place and fluid gets discharged
   
   

Types of Gear Pump
There are mainly two types of gear Pumps classified on basis of their design:

1. Internal Gear Pump
   
2. External Gear Pump
   
   Internal Gear Pump
   
   
   
   As depicted in Fig. 4, the inner gear is smaller and has outer teeth and the outer gear is the larger gear and has inner teeth. As the two gear teeth mesh together a vacuum is created causing liquid to enter between the gap. The trapped fluid then travels to the outlet to be discharged.
   
   External Gear Pump
   
   
   Fig. 5, depicts an External gear pump where meshing of a pair of helical or spur gears whose external teeth are meshed with each other and placed inside a casing. One of the two gears is the driving gear and the other one is driven gear. When the driver gear is rotating, the driven gear also rotates as the teeth are meshed together. The rotation of the gears produces a partial vacuum which creates enough suction at the inlet to let liquid enter the pump. At the discharge side a high pressure is produced to discharge the liquid through the outlet.