Internal Gear Pumps

Internal gear pumps are not gear pumps that go inside machinery. They are pumps with a ring gear and an internal gear that revolves around inside this ring gear. So the fluid is contained internally between the ring gear and the driven gear. There are two types of internal gear pump. The normal gerotor type, sometimes called gerolor, shown in Figure 2, and the spur gear type pump which uses a different type of gears. Internal Gerotor Gear Pump Figure 1 shows the inside view of a basic gerotor gear pump. The name is derived from the words Generated Rotor, coined by the father of the gerotor design, Myron F. Hill who spent many years developing the geometric theory in the early 1900’s. These pumps work similar to the spur type gear pump but without the crescent between the rotor (the internal drive gear) and the idler (the external driven gear). The driven gear has one extra tooth than the drive gear and the drive shaft attached to the drive gear is offset just enough to allow the gears to mesh neatly at the top. As you can see, these are not spur gears but are designed so that they seal together continuously as they rotate. This rotation causes a vacuum to be created on the inlet side so that fluid is sucked into the cavity between the gears. The cavity gets bigger as the tooth approaches the botttom point then gradually gets smaller. The smaller the cavity gets the more pressure is placed onto the fluid which forces it out the outlet to travel through the circuit. Gerotor pumps are widely used today, and are manufactured in a variety of shapes and sizes by many companies like EATON, Parker, Bosch Rexroth etc. Uses Gerotor pumps are used in a variety of applications like, oil pumps, fuel pumps, high speed gas compressors and can even function as a pistonless rotary engine. They are suitable for clean, low pressure applications such as lubrication systems or hot oil filtration systems, but can also be found in low to moderate pressure hydraulic applications. Advantages The advantages of using a gerotor pump are: High speed operation, they have fewer moving parts, there is constant and even discharge regardless of pressure (they are a positive displacement pump), they operate equally well in either direction and they are quiet in operation. Disadvantages The disadvantages of using a gerotor pump are: They have medium pressure limitations, they have fixed clearances, they do not handle solids very well and the shaft bearing has to handle an overhanging load. Applications Gerotor pumps are used to pump: Light fuel oils, lube oils, cooking oils and hydraulic fluid. Remember, at Central Qld Hydraulics, we take any old pumps and motors that are preserved well, replace their damaged parts to make them go on doing their outstanding work as new pumps and motors.

A description of how a gerotor pump works

CENTRAL QUEENSLAND HYDRAULICS