Off-cenered internal gear pump
The drive gear is attached directly to the drive shaft of the pump and is placed off-center in relation to the internal gear. The two gear mesh on one side of the pump, between the suction (inlet) and discharge ports. On the opposite side of the chamber, a crescent-shaped form fitted to a close tolerance fills the space between the two gears. The rotation of the center gear by the drive shaft causes the outside gear to rotate, since the two are meshed. Everything in the chamber rotates except the crescent. This causes liquid to be trapped in the gear spaces as they pass the crescent. The liquid is carried from the suction port to the discharge port where it is forced out of the pump by the meshing of the gears. The size of the crescent that separates the internal and external gears determines the volume delivery of the pump. A small crescent allows more volume of liquid per revolution than a larger crescent.
IV. Answer the following questions to the text:
1. What is the difference between the helical gear pump and the spur gear pump?
2. How are the pumping gears driven?
3. What can you say about the operation of off-centered internal gear pump?
VI.Give a short summary of Text 6
UNIT 7
Translate the text with a dictionary in written form
LOBE PUMP
The lobe operation as pump uses the same principle of the external gear pump described previously. The lobes are considerably larger than gear teeth, but there are only two or three lobes on each rotor. The two elements are rotated, one directly driven by the source of power, and the other through timing gears. As the elements rotate, liquid is trapped between two lobes of each rotor and the walls of the pump chamber and carried around from the suction side to the discharge side of the pump. As liquid leaves the suction chamber, the pressure in the suction chamber is lowered, and additional liquid is forced into the chamber from the reservoir. The lobes are constructed so there is a continuous seal at the points where they meet at the center of the pump. The lobes of the pump are fitted with small vanes at the outer edge to improve the seal of the pump. Although these vanes are mechanically held in there slots, they are, to some extent, free to move outward. Centrifugal force keeps the vanes snug against the chamber and the other rotating members.
UNIT 8
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