Graseby 3000/500, Manual

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5 — 1 1
G r a s e b y M e d i c a l L t d .
5
3 0 0 0 / 3 1 0 0 a n d 5 0 0 / 5 0 5 S e r v i c e M a n u a l I s s u e A ( A p r i l 2 0 0 2 )
V o l u m e t r i c I n f u s i o n P u m p s
Photo sensor
The pump systems include a photo sensor device used to monitor
ambient light levels and adjust the LED display intensities
accordingly. The photo sensor is a photoconductive cell which has a
cell resistance that varies inversely with illuminance. The cell
resistance varies from approximately 10K ohms to approximately 1M
ohms. The cell is designed into one leg of a resistor divider network
and the voltage generated across the cell is read by the display board
micro-processor via the 8-bit analog to digital converter.
Over pressure valve and swing arm
The over pressure valve (item 24, Fig. 5.3) is located directly below
the over pressure piston (item 22). The swing arm (item 2) is attached
to the cam housing at the rear of the over pressure valve shaft. The
toothed section of the swing arm engages the motor coupler and is
held in ready position by a torsion spring. The swing arm rides on the
toothed surface of the motor coupler while the pump is running.
When the motor backs off, the swing arm catches on the motor
coupler and forces the over pressure valve outward, occluding the
fluid pathway. In this way, reverse fluid flow is prevented whenever
the pumping mechanism backs off.
In the event an administration set is loaded improperly, excess
pressure can build up in the cassette. If this happens the pump
alarms and remains on hold. During this period, the excess pressure
within the cassette pushes the pressure plate away from the cassette
housing. In this situation the pressure spring, mounted on the over
pressure valve shaft, forces the valve outward, keeping it in contact
with the pressure plate and preventing free flow.
Back pressure regulation
Proper performance of the pump depends on constant conformity of
the fluid filled cassette to the cassette housing and pistons during the
pumping cycle. A small amount of pressure within the cassette is
therefore needed to maintain proper cassette form. The over
pressure valve (item 24, Fig. 5.3) and the over pressure piston (item
22) function together to create a resistance to the fluid flow for the
purpose of providing this needed pressure. Internal cassette pressure
must be great enough to maintain cassette form, yet kept below the
threshold of the Low Occlusion Alarm Setting.
The over pressure valve restricts fluid flow during operation which
results in internal cassette pressure. The position of the over
pressure valve and resulting pressure is influenced by the over
pressure piston.
The over pressure piston and valve are coupled by a vertical connect
shaft (item 23). The over pressure piston is slotted where it joins the
connect shaft. This slot allows semi-independent movement between
the valve and piston.