Biomedical Engineering Reference
In-Depth Information
FIGURE 8-71
Schematic diagram
of a peristaltic pump.
8.7.2.3 Peristaltic Pumps
Peristaltic pumps are based on an elastomeric tube through which the fluid is forced by
the action of a number of lobes or rollers that progressively squeeze along its length, as
illustrated in Figure 8-71. The tube should be closed by at least one lobe/roller at all times
throughout the pumping cycle. The squeezing items are generally located on the rotating
support, which is driven by a variable speed drive. This mechanism includes no glands
and is very smooth operating.
The flow rate of the pump is related directly to the diameter of the tube and the speed
of rotation of the drive. The pump duty is limited by the tube material used in construction.
The suction capability is related to the tube's ability to rapidly expand after the compression
cycle. This pump type can generate heads of up to5matflowsofupto10m
3
/hr.
8.7.3 Reciprocating Pump Characteristics
The two primary forms of reciprocating pumps used in medical applications are piston
and diaphragm pumps.
8.7.3.1 Reciprocating Piston Pumps
In a reciprocating piston pump, a motor-driven cam pulls the piston back and forth in the
pump head, as shown in Figure 8-72. A flexible seal around the periphery of the piston
prevents leakage of the liquid from the back of the pump. Check valves mounted in the
head open and close in response to small changes in pressure to maintain a one-way flow
of the liquid.
During the intake stroke, reciprocating cylinder pumps increase the volume of the
pump cavity, which reduces the pressure and draws the liquid in through an inlet valve.
FIGURE 8-72
Schematic diagram
of a reciprocating
piston pump.
