What Is Gear Pump ? – Construction, Design & Working

Gear Pump Working Explained

What is gear pump? A gear pump is a type of positive displacement constant delivery rotary pump. What it means is that it generate a constant amount It converts mechanical energy into fluid energy creating void suction with the help of its gear meshing. The space left between these gear meshing suck in the high viscous fluids displacing it along the walls of the casing and then towards the output.

A gear pump is well suited for high viscous fluid such as oil as it does not require priming; do not mix or emulsify the fluid, is efficient and have high pressure head with tolerance to small particles. This might rise doubts and questions in your mind ” Whether a gear pump be used for Water ? “.

Can Gear Pump Be Used For Water?

In theory ” YES ” a gear pump can be used to pump water as long as the suction is filled with liquid water. A gear pump is not preferred for water application; as water does not holds lubricating property and thus leads to erosion of gear teeth. Furthermore, gear pumps have a tendency to slip with low viscous fluids such as water affecting the final output pressure.

Slip is the phenomenon of recirculating parts of the output back to the suction via the internal clearance in the gear pump. An increase in slip decrease the overall efficiency of the pump making it uneconomical for water applications.

Gear Pump Design and Construction

A gear pump contains two or more rotating gears inside a casing with high tolerance in between casing and the gears. Inlet and outlet points are made in pump casing for proper fluid transfer. Based on its design a gear pump can be of external or internal gear type.

In external gear pump identical gears are positioned side by side to each other; with one connected to the motor; which then drive the other gear. On other hand a small idler or driven gear is positioned within the large rotor gear in internal gear pumps.

The external gear types are the most common gear pumps used due to their low cost and good performance under high pressure. They can be either unidirectional or bi-directional based on the design; have low noise level, compact design, excellent performance and better reliability.

Generally helical gear pump is preferred over spur gear pump; due to better working behavior of one over another. However spur gear pump are constructionally simpler and cheaper than their counterpart; So correct gear type is chosen based on the required parameters. For gear pumps the fluid displacement per gear teeth rotation is calculated by:-

Q = 0zt0Vndt

And,

Flow fluctuation ( η ) = Vmax  VminVav

Here,

Q = Fluid Displacement

Z = Number of teeth Associated

Vn = Volume flow rate of liquid.

t0 = Time per teeth rotation.

Vmax = Maximum volume flow rate

Vmin = Minimum volume flow rate

Vav = Average flow rate.

Gear Pump

How Do Gear Pump Work?

When two toothed wheel rotate inside a closed casing air is trapped between the two teeth and along the teeth and casing making vacuum. This results in a positive upward lift of fluid towards the suction port of the pump. the pump will continue to suck in air as long as it starts to get continues supply of fluid at its inlet side.

The fluid will be sucked in at atmospheric pressure; before being trapped in-between the teeth of the two wheels. Slowly the viscous fluid will be dragged towards the output and pumped outwards. The pump works well even in idle condition but performs even better when already primmed. On ship these pumps are used as lube oil pump, fuel oil transfer pump and boiler fuel oil pump.

Additional safety in form of relief valve are installed in gear type rotatory pump to avoid any damage to the pump or the pipeline. The relief valve will reduce excessive pressure in event of fault or emergency; protecting equipment and the surroundings.

What is Backlash in Gear Pump And Its Use?

A backlash is the small gap left after the teeth to teeth meeting with one another during normal operation of the pump. It can be both desirable as well as undesirable based on the situation. For example a backlash restricts quick and easy reversing of gear pumps; on other hands it also allow for proper lubrication preventing jamming or seizure of gear teeth. This also plays a key role in maintaining proper bearing life and avoid overheating.

The main advantages of having appropriate backlash in between gear is:-

  1. Reduced Noise
  2. Better Lubrication
  3. Avoid Over heating
  4. Smooth Operation
  5. No need to construct pumps with high accuracy.

Gear Pump Working Animation

Advantages and Disadvantages of Gear Pump

Gear pumps can be used for a variety of application but is preferred and limited to high viscous fluids. The main advantages and disadvantages of these pumps are:-

Advantage

  • Cheap / Economical
  • High R.P.M
  • Reliable
  • Reversible
  • Simple Design
  • Controlled Output
  • Self Primmed
  • Less Susceptible to cavitation.
  • Works for a large variety of viscous fluids.

Disadvantages

  • Can become inefficient due to cavitation or erosion
  • Can be noisy
  • Don’t work well with large amount of abrasive particles.
  • Do not work well for water and other low viscous fluids.

Difference Between Gear Pump And Centrifugal Pump

 

Gear Pump
Centrifugal Pump
It is a type of positive displacement pump
It is a dynamic pressure pump
These pumps are used mainly for high viscous fluids such as oil.
These pumps are used for low viscous fluids such as water
Gear pumps are used for high head low flow application.
Centrifugal pump are used for low head high flow application.
High Efficiency
Low efficiency
Cheap and simple
Simple but relatively costly
Less Prone to cavitation
High prone to cavitation
Self primed
Require primming
It use gear teeth to transfer fluid.
Use impeller to transfer fluid.
Require close clearance and precision of parts
Does not require such close clearance and precision of parts.
Can be reversed without adverse effects.
Can not be reversed without adverse effects.

Maintenance

Proper maintenance and housekeeping is the most important aspect of smooth operation of gear pump. A proper records of past maintenance / repairs, performance and replacement will help determine the performance of pump in the future. Check for the working of pressure regulating valve to ensure safety in case of over pressure.

Flow switch if installed must be checked for working to avoid dry running of the pumps. A gear pump when run dry leads to localized overheating and  wearing of gear teeth. Bearings of pump must be replaced in each major overhaul; bearings are susceptible to most damage leading to misalignment and imbalance of gear pump.

Check for the condition of bearings on each maintenance and change if necessary or in each major overhaul. Any abnormal noise or sudden increase in pump noise is a clear indication of bearing failure by worn out or damaged; and need to replaced.

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