This is a type of Rotary Force Pump. Gear pumps are extremely simple and reliable.
Depending on the number of teeth, the “idler” gear might be driven directly by the “drive” gear. Generally with six or more teeth this is possible. In other cases an extra gear external to the pump drives the secondary gear at the same rate.
The teeth on Gear Pumps can be spur (straight), helical (slanted), herringbone, etc. There can be two, or more teeth on each gear — twenty is not uncommon. The diameter of the gears and their thickness varies widely.
The many variations have different effects on the efficiency, strength, smoothness and other areas of operation.
This pump will pump in the reverse direction if you reverse the direction of rotation of the gears. Two pairs of valves can be added to make this a Reversing Gear Pump, which pumps in the same direction regardless of which direction the gears rotate
Gear Pump, Balanced
This is a modification of a regular Gear Pump and all the variations in that pump (number of teeth, size, shape, etc.) are possible here too.
The tubing around the edges of this pump returns pressure — not liquid — to opposite sides of the shafts. Very little fluid is transferred anywhere by these extra tubes.
By equalizing pressure on each side of the shafts, friction and wear are both reduced in comparison to the standard gear pump.
Other types of pumps, such as Vane Pumps, sometimes are balanced in similar ways.
Gear Pump, 2-lobe
This type of gear pump has two lobes on each shaft. The lobes nearly touch each other in the center forming a fairly tight seal.
They also nearly touch the casing and when they revolve they carry fluid around the outer edge to the outlet, at the top in this drawing.
This type of gear pump, or a three-lobe version, is often used as a supercharger for diesel engines, forcing air (not liquid) into the power cylinder.
Gear Pump, 3-Lobe
This is a basically a type of Gear Pump but with lobes instead of gears.
The three-lobe gear pump, like the two-lobe version, is commonly used to force high-pressure air into combustion compartments of a diesel engine.
The output of these pumps is more pulsed than the output of a gear pump because there are fewer teeth. The fluid is delivered in comparatively larger packets.
Gases are compressible (whereas liquids basically are not), therefore the three lobe and two lobe gear pumps work particularly well with gases, since the compressibility helps smooth the flow.
Gear Pump, Reversing
This type of rotary gear pump moves liquid in the same direction regardless of the direction the gears turn.
The valves are forced open and closed by the difference in pressure on the input and output sides.
In this drawing, fluid in the higher-pressure output side is shown in light blue while fluid in the lower-pressure input side is dark blue.
Notice that when the green gear starts moving clockwise, the fluid in the outer circular tubes changes pressure but stops flowing, and fluid flows more or less straight up.
When the red gear is moving clockwise, fluid travels in a sideways ‘S’ shape through the outer circular tubes.
The pump in this drawing reverses direction about every 8 seconds.