Crescent Pump (from Internet Glossary of Pumps)
Crescent Pump
This pump consists of two rotating gears; an Internal Gear with the teeth on the outside, and an External gear with the teeth on the inside. The External Gear is larger and has more teeth, but the teeth are the same size.

As the teeth separate (lower left side in this drawing) they pass over the intake hole (shown behind the gears in black on the left). They "suck" in fluid, then the gears are separated by a Crescent Seal (shown in brown.)

When the teeth start to come together again (upper right here) they squeeze the fluid through the outlet hole (shown in black at the top center of this drawing.)

Normally the inner gear is attached to a drive shaft and the outer gear is turned by the inner gear at the point of contact (upper left area of this drawing.)

Advantages of the crescent pump include its simple design and low maintenance requirements. The crescent pump is common in many applications including automatic transmissions.

(This is a 20-frame animation, converted to animated GIF format and then super-compressed for Internet transmission. (Note: On some Internet browsers it may be displayed much less smoothly than the CD-ROM version, where the frames are timed to a thousandth of a second.))

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Last modified February, 2002
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