Biomedical Engineering Reference
In-Depth Information
to peristaltic systems, more pump heads are required to dose at the same rate
as the equivalent piston, time pressure, or rolling diaphragm systems.
The current single-use, presterilized dosing systems are based on scal-
ing-up technologies designed and used for small-scale filling operations.
However, a better approach is to convert existing high-speed dosing tech-
nology to single-use. The three most common commercial systems are piston
pumps, rolling diaphragm pumps, and time pressure dosing. All three of
these systems require significant technical improvements and modifications
to be converted to disposable use.
Piston pumps rely on a precise physical tolerance between the pump body
and piston to provide dosing accuracy and to ensure the product does not
leak during use. Pump bodies and pistons are commonly matched when they
are fabricated to ensure they do not gall during use. Existing piston pumps
for pharmaceutical dosing can be made using stainless steel or ceramic com-
ponents. Neither material can be used to make a disposable pump due to the
high cost of manufacture. Plastic components are an alternative but cannot
be fabricated to the correct tolerances to ensure accuracy. Excessive wear and
leaking would also be issues. A catastrophic loss of function will likely result
without the use of o-rings, a lubricant, or both to separate the moving plastic
surfaces. Plastic particles, elastomeric particles in the case of o-ring use, or
lubricant will also be shed by the pump and introduced into the product
stream (see
Figure 9.1
).
The rolling diaphragm pump, originally developed by TL Systems (now
part of Bosch), comprises a stainless steel pump with a diaphragm. A head-
piece and diaphragm make up the liquid chamber. Dosing occurs by actu-
ating a piston that is attached to the diaphragm. It is very similar to piston
dosing, only the diaphragm keeps the product from contact with the piston
and other internal components. The only stainless steel part in contact with
the product is the headpiece (see
Figure 9.2
). Unlike the piston pump, how-
ever, these surfaces are separated from the fluid path by the diaphragm, so
contamination of the product stream will not be an issue. The tolerances
for each part are not as critical as with piston pumps, as dose accuracy is
related to accurate piston stroke while at the same time maintaining consis-
tent dimensions in the fluid chamber.
Time pressure systems are designed to dispense using a pressurized prod-
uct supply and timed valve openings (see
Figure 9.3
). A portion of the product
path from the product supply manifold to the filling nozzles is made of elas-
tomeric tubing. This tubing is used in association with an automatic tubing
pinch mechanism to create the valve. The use of disposable tubing seems to
make the system a good candidate for a single-use system. However, this is
not the case. These systems often use a small surge tank for the product sup-
ply, and this tank must be pressurized up to 10 psig or more for the system
to function. Replacing this tank with a bag would require that the bag be
pressurized beyond its normal design pressure. There is currently no good
