Hospira LifeCare XL Series, Техническое и сервисное руководство

Страница: 41 / 278

SECTION 4 THEORY OF OPERATION
430-00587-008 (Rev. 2/05) 4 - 16 Plum XL Series
4.3
MECHANICAL OVERVIEW
The principal mechanical elements of the infusion system include the cassette and the
mechanism assembly. When a cassette is locked into the operating position and the control
knob is turned on, the infusion system performs a self test to verify the integrity of the
internal systems. The operation of the mechanism assembly moves a plunger, causing a
pumping action. A valve motor selects the primary or secondary valve, depending on the
command. An additional valve motor alternately opens and closes an inlet valve and outlet
valve to control fluid flow through the cassette pumping chamber.
The following sections detail the cassette and the mechanism assembly.
4.3.1
CASSETTE
The cassette operates on a fluid displacement principle to volumetrically deliver fluid
(see Figure 4-1, Major Elements of the Dual-Channel Cassette , and Figure 4-2, Fluid Path
in the Cassette) . Refer to the system operating manual for a description of the major
cassette functions.
The pumping cycle begins when the outlet valve is opened and the inlet valve is closed.
The plunger extends to deflect the cassette diaphragm and expel fluid. At the end of the
pumping stroke, the outlet valve closes, the inlet opens, the appropriate primary or
secondary valve opens, and the plunger retracts to allow fluid to refill the pumping
chamber. After the pumping chamber is filled, the inlet and outlet valves are reversed, the
primary and secondary valves are closed, and the cycle is repeated.
The cassette contains two chambers: an upper air trap chamber and a pumping chamber.
The two chambers are separated by an inlet valve
(see Figure 4-1 and Figure 4-2) and
operate together to detect air. The upper air-trap chamber receives fluid from the
intravenous (IV) container through either the primary or secondary valve. The upper
air-trap chamber collects air bubbles from the IV line and container to prevent them from
entering the pumping chamber; the chamber can collect a substantial amount of air. The
controller tracks the amount of air collected in the upper air-trap chamber. If a
predetermined air collection threshold is exceeded, the controller starts an infusion system
backprime and initiates a secondary display.
A proximal air-in-line sensor (bubble detector) is located between the primary/secondary
valves and the upper air-trap chamber. The proximal air-in-line sensor detects air entering
the upper air-trap chamber and initiates an audible alarm if the predetermined air
collection threshold is exceeded. Similarly, a second air-in-line sensor located distal to the
pumping chamber initiates an audible alarm if a predetermined amount of air is detected.
The pumping chamber receives fluid from the upper air-trap chamber through an inlet
valve. When the diaphragm covering the pumping chamber is deflected by the plunger,
the pumping chamber expels fluid through an outlet valve. A pressure sensor located distal
to the pumping chamber monitors pressure on the distal side of the cassette.
A flow regulator is incorporated into the cassette distal end. This flow regulator is used to
manually control flow when the cassette is not inserted in the pump. When the cassette
is properly inserted into the infusion system and the infusion system door is closed, a
mechanism opens the flow regulator to allow the infusion system to control fluid flow.
When the infusion system door is opened, the same mechanism closes the flow regulator
to disable fluid flow.