Smiths Graseby 3200, Technical & Service Manual

Page: 39 / 117

Smiths Medical International Ltd.
3200 Service Manual Issue 5 (August 2004)
3 — 2
When the plunger clamp is pulled down, the half nut/super nut engages with the leadscrew
and the clamp engages with the end of the syringe.
The syringe plunger slots into place behind a slotted pair of lips. These lips prevent the
syringe plunger from moving forward in the event of negative pressure on the syringe.
Two small push-buttons on the edge of the plunger clamp make contact with the top of the
syringe plunger. These push-buttons control the operation of a lever which protrudes from
the plunger clamp.
When the push-buttons are pressed in, by coming into contact with the top of the syringe,
the lever becomes free and is able to retract into the plunger clamp. This retraction takes
place when the plunger clamp is physically swung into its down operating position.
If the push-buttons are not pressed ‘in’, the lever is locked in its protruding position thus
preventing the plunger clamp from being pulled down. This in turn prevents the half nut
from engaging on the leadscrew.
This push-button safety system prevents the leadscrew from being engaged unless the
top of the syringe is correctly positioned in the plunger clamp.
If the plunger clamp is accidentally dislodged during an infusion, the pump will automatically
and safely stop infusing. The alarm will sound.
Plunger clamp
An occlusion sensing assembly located at the left hand end of the leadscrew ( Figure 7.1 )
causes the rotating leadscrew to turn a slotted disc. The rotation of this disc is detected
by an opto-sensor.
A spring mechanism at the right hand end of the leadscrew provides the pressure that is
required in order to overcome any slight resistance from the syringe plunger.
If an occlusion occurs in the syringe line and the occlusion pressure is sufficient to over-
come the spring pressure, the leadscrew moves slightly to the right, thus losing contact
with the clutch. The slotted disc stops rotating. This non-rotation of the slotted disc is
detected by the opto sensor and an occlusion alarm is generated.
This method of occlusion detection is extremely sensitive as it is the lack of pressure on
the clutch that generates the alarm, rather than a detection of the movement of the
leadscrew, as used in traditional designs (UK patent no. 2249497).
Internal occlusion system
The method of directly measuring the pressure in the infusion line allows a more accurate
measurement of the lower occlusion pressures to be made, thereby making the pump
ideally suited for neonatal infusions.
The infusate flows through a disposable pressure sensing disc which is part of the pres-
sure sensing assembly (
Figure 7.1 ).
The sensing disc has a chamber which is covered by an elastic membrane. As the pres-
sure in the infusion line increases, the pressure exerted on the membrane also increases.
The membrane in turn presses against a pressure transducer mounted on the side of the
pump. The pressure transducer is covered by an insulating film to prevent the ingress of
foreign particles.
(contd.)
In-line occlusion system
Occlusion system