Smiths Graseby 3200, Technical & Service Manual

Page: 34 / 117

Smiths Medical International Ltd.
3200 Service Manual Issue 5 (August 2004)
2 — 12
Occlusion thrust
Occlusion
measurements
Thrust
measurements
Syringe
stiction
The two most frequently used methods to measure the point at which an occlusion
occurs are the
thrust and pressure methods.
Currently, the occlusion is set in the factory by using a thrust measurement procedure.
This method measures the plunger clamp thrust by using a set of weights (see next page).
The occlusion pressure is obtained by measuring the pressure that occurs in the infusion
line. The in-line method requires the use of a new syringe and infusion line. Conversion
between the two is achieved using the formulae below, taking into consideration syringe
stiction.
The 3200 has the ability to measure in-line occlusion pressure, when using the dedicated
disposal. See page 3-2.
The internal occlusion sensing system within the pump is always active.
Translation of the thrust depends on the syringe diameter and the stiction of the syringe.
The formula for calculating the thrust is given below:
T = P x A +S
732 1
where: T = thrust in kg.
P = delivery pressure in mmHg.
A = cross sectional area of the syringe in cm 2 .
and S = syringe stiction in kg.
The occlusion thrust of the pump is factory set to be between two limits (i.e. a minimum
and a maximum tolerance). The customer may reset the thrust for their own particular
requirement. The thrust of a pump may, therefore, differ from the original factory set
levels.
The occlusion thrust of the 3200 pump is factory set to be between 3.5 kg and 4.2 kg (471
mmHg and 565 mmHg).
Stiction for a syringe varies from brand to brand as well as from batch to batch. Stiction
can be as low as 0.1 kg and as high as 2 kg. The stiction of some syringe brands has been
found to be particularly high.
Stiction can also vary along the plunger travel and is usually lowest in small diameter
syringes. Using a sample syringe and allowing for a safety margin for sticky syringes,
adjustments can be made by measuring the thrust generated. If the stiction characteristics
of a syringe are known then by using the formula given above the occlusion thrust can be
set.