Biomedical Engineering Reference
In-Depth Information
FIGURE 8-69
Schematic diagram
showing gear pump
construction.
The gear pump has moderate efficiency, and it not recommended for handling sus-
pended solids. Because the gears are in contact, the fluid can be highly sheared as it is
transferred. These pumps can transfer fluids at reasonable flow rates at developed heads
of up to 200 bar if designed correctly.
8.7.2.2 Lobe Pumps
Lobe pumps are based on two parallel rotors located within a shaped case, as illustrated
in Figure 8-70. The rotors include a number of lobes that are arranged so that as the rotors
turn they contain spaces that increase and reduce in volume. Fluid enters these spaces
through the inlet connection and is trapped as the rotors turn until it is discharged through
the outlet port. The rotors are synchronized by external gears, and therefore the internal
contact between the lobes is a sealing contact and not a driving contact.
Various shapes of rotor are used, with the trilobe rotor being the most popular. The
lower the number of lobes the better the pump is for handling viscous and solids-laden
fluids. The rotor can be made from a wide range of materials including steel and reinforced
rubber. When soft rotors are used this type of pump can achieve high levels of volumetic
efficiency.
Lobe pumps generate relatively low internal fluid velocities with low level of shear
and are therefore suitable for blood pumps. The resulting flow includes some pulsation.
The pump can also run dry without damage, subject to the design of the bearings. It is
also self-priming if the rotors are wetted. As the pump has clean internal surface with few
crevices it can be used for hygiene-related applications.
FIGURE 8-70
Lobe pump
schematic diagram.
