112 Module 9 • Pumps Vane-type pumps
Te pump consists of a cylindrical housing in which a rotor is fitted eccentrically so that it almost touches the inside of the housing at a point between the ports. In the rotor, there are sliding slots into which two or more vanes are fitted. Tey are held apart by a spring so that the tips of the vanes are always in contact with the housing. Inlet and outlet ports are cut into the housing.
rebound spring sliding groove
trapped fluid
rotor seal vane casing/housing
moving vanes/ blades
outlet port
seal Figure 9.8 A vane pump
intlet port
Vane pumps are efficient at speeds over 600 rpm, which corresponds to a maximum sealing of the vanes against the cavity due to centrifugal load. Below this speed, leakage is high. Te rotor is driven by a shaſt which, in turn, is driven by the camshaſt.
Operation
• When one of the vanes moves past the inlet port, the space between this vane, the rotor and the housing increases gradually.
• Tis causes a vacuum in the space, which causes oil to be drawn from the sump.
• When the next vane moves past the inlet port, the oil is trapped and is carried along by the rotating rotor.
• Due to the eccentric rotor, the space now decreases and the oil is pressurised. • Te first vane now moves past the outlet port while the space still decreases.
• Te decreasing space and the next vane force the oil through the outlet port to the oil channels.
Flexible impeller pumps
Tis type of pump is basically the same as a vane pump in that the rotor with flexible vanes is mounted concentrically in a circular housing which has a flattened area on the one side. Tis flattened side provides the eccentric path for the impeller.
outlet/ discharge
offset cam flat side inlet
volume contracting (pressure)
base flexible impellers/vanes Figure 9.9 A Flexible impeller pump
volume expanding (suction)
direction of rotation
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