What's a gear pump?

ani_pump_medium.gif (17013 bytes) title-gear_pumps.jpg (3149 bytes) ani_pump_medium.gif (17013 bytes) TITLE: How A Gear Pump Works AUTHOR: Martin L. Culpepper COURSE:2 YEAR: G MAIN FUNCTIONAL REQUIREMENT: Convert mechanical power into fluid power. DESIGN PARAMETER: Pump (a gear pump is one type of pump which can satisfy this functional requirement) GEOMETRY/STRUCTURE AND PARTS: real_pump_front_view.jpg (8010 bytes) real_gear_pump_exploded.jpg (30840 bytes) EXPLANATION OF HOW IT WORKS: flow_thru_gear_pump.gif (7137 bytes) One shaft is driven by a motor or some other means The gear mounted to this shaft (driving gear) engages the other gear (driven gear) Fluid on the inlet side flows into and is trapped between the rotating gear teeth and the housing The fluid is carried around the outside of the gears to the outlet side of the pump As the fluid can not seep back along the path it came, nor between the engaged gear teeth (they create a seal,) it must exit the outlet port. In some gear pumps, there are side plates usually made of brass which can be replaced or re-ground when the gap between the face of the gear and the end housing becomes too large DOMINANT PHYSICS: Variable Description Metric Units English Units Pin Power input to shaft Watts Horsepower Pout Power output to fluid system Watts Horsepower Ploss Power loss (i.e. to coloumb friction and viscous dissipation) Watts Horsepower w Shaft rotational speed rad/s RPM Dp Pressure increase between inlet and outlet Pascals psi Q Flow rate through the pump liters3/s in3/s hm Mechanical efficiency --- --- The pump takes power from a rotating shaft: Pin = T x w A portion of this power is dissipated in the pump through coloumb friction and viscous dissipation. This is not easily quantified theoretically and is often determined experimentally. This power will be denoted at Ploss. Ploss = f(friction, viscous effects......) Some fluid will seep through the gap between the sides of the gears and the endplates (see figure below.) This gap must be small in order to maintain the pressure increase across the pump. Increasing the gap diminishes the pumps ability to hold a pressure difference between the inlet and outlet. The gap is typically around0.0005 inches. gear_pump_gear_face_leakage.gif (8072 bytes) The power which can then be derived from the fluid which comes out of the pump is: Pout = (Dp x Q) = Pin - Ploss = T x w - Ploss This can also be expressed using the efficiency: Pout = hm x Pin LIMITING PHYSICS The performance/use of the pump is limited by its: Efficiency hm=of a pump is Pout/Pin. This is a function of the fluid viscosity, clearance between internal components, friction between mating components, and other variables. Typically, gear pumps have efficiencies around85%. Bearings Many external gear pumps use journal bearings to support the rotating shafts. In order for these bearings to work, a minimum speed is required (depends upon pressure of the pump.) In addition to imposing limits on the operational speed, in many cases, the bearings determine the maximum pressure the pump can operate at. Should the pressure drop across the pump be too large, the journal bearings will not be able to support the loads on the shafts (which come mainly from the pressure difference.) IF NEEDED, PLOTS/GRAPHS/TABLES: None to include here WHERE YOU CAN FIND GEAR PUMPS: These pumps have few moving parts, making them inexpensive. These pumps are typically used where low to medium pressure (about2500 -4000 psi) is needed and mechanical efficiency is not extremely important (typical efficiency is about85%.) You can find gear pumps on the following machines: Usually your car's oil pump Hydraulically driven lawn care equipment Some hydraulically driven log splitters Hydraulic power units on trucks and construction equipment Metering applications (gear pumps are good at controlling volume flow rate)

A gear pump uses the meshing of gears to pump fluid by displacement. They are one of the most common types of pumps for hydraulic fluid power applications. Gear pumps are also widely used in chemical installations to pump high viscosity fluids.

A gear pump uses the meshing of gears to pump fluid by displacement. They are one of the most common types of pumps for hydraulic fluid power applications. 

1. Gear pumps are positive displacement (or fixed displacement), meaning they pump a constant amount of fluid for each revolution. Some gear pumps are designed to function as either a motor or a pump.
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