The technology of moist-heat sterilization in counterpressure has been developed specifically for the terminal treatment of solutions in closed containers.

Its primary aim is to "neutralize" the effects of the overpressure which unavoidably forms inside containers when they are sterilized using conventional saturated-steam autoclaves.

This overpressure tends to make glass containers explode and to lift their stoppers, irreversibly deforms flexible -or rigid- plastic containers, expels the plungers of prefilled-syringes, etc.

The collateral but not at all secondary aim is to perform load cooling with a sterile fluid, either water or air, thus complying with the CGMP of the F.D.A. for LVP.

Counterpressure autoclaves currently in use belong to two types:
• superheated water spray autoclaves
• steam+air mixture autoclaves

To a certain extent, the two types are complementary and our company has built both for several years. They are also presented together in this brochure, highlighting as clearly as possible the relative advantages of the two types.

The figure above shows some typical products which can be sterilized with these autoclaves. This presentation is absolutely non-limitative, and new packages which require careful use of counterpressure sterilization are constantly being introduced in the market.

Our Customers should contact us during the development of their new products/packages, since often modest adaptations of these products/ packages allows optimisation of the results of the sterilization processes.
Our Research & Development Service is at the disposal of our Customers for this purpose.

FOW autoclaves are based on an extremely straightforward operating principle which is applied with a highly reliable and mechanically very simple unit.

When the program begins, after the load to be sterilized has been introduced, only the lower part of the chamber is filled with treated water of adequate microbiological quality. The chamber has a circular cross-section with a single wall, but has rectangular doors inscribed in the circle. The air inside the chamber is not removed.

The water, which is drawn from the bottom of the chamber by a sanitary-type centrifugal pump, is circulated through a moving-plate heat exchanger, also of the

sanitary type, which is indirectly heated in countercurrent with mains steam.
The water is then fed back into the upper part of the chamber and is distributed onto the load by a system of solid-cone spray nozzles.
Water redistribution onto the lower layers of the load is ensured by appropriate perforated supporting shelves.




Moving-plate heat exchanger made of stainless steel, sanitary type, double function (heating/cooling). Combines maximum efficiency and maximum safety. Plate cleaning is spontaneously ensured by the turbulence, speed and alternation of the circulation fluids (steam and cooling water).

Sanitary type centrifugal pumps ensure an extremely high water circulation speed, which is essential to obtain optimum temperature uniformity.

Heating of the circulation water and thus of the load is gradual but quite fast. The sterilization temperature of 121°C is reached within approximately 25-30 minutes inside 500 ml containers.
After the sterilization time (approximately 20 minutes) has elapsed, the circulation water, which by then is sterile as well, continues to circulate through the exchanger, which however in this step is supplied with top cold cooling water.

Within approximately 10 minutes, the temperature inside the containers (again assumed to have a 500 ml capacity) gradually drops to approximately 80° C, which is the ideal temperature to also obtain rapid and spontaneous drying of the load extracted from the autoclave.
The entire process therefore lasts approximately 60 minutes.

Throughout the process, an adequate counterpressure of sterile air is maintained inside the chamber in order to counterbalance, in the most appropriate and automatic manner, the overpressure which is present at most times within the containers.

FOA
AIR+STEAM MIXTURE AUTOCLAVES

FOA autoclaves have a chamber with a circular cross-section, generally with a single wall, and with rectangular doors inscribed in the circle. In these autoclaves, too, the air inside the chamber is not removed.
The program begins by introducing steam directly in the chamber by means of the sparger located in the lower circular sector.

One or more fans are located in the upper circular sector; their number depends on the depth of the chamber. The fans generally have a vertical axis: in case of particular

load requirements, it is also possible to install fans with a horizontal axis which are obviously placed in one of the lateral circular sectors of the chamber.

The action of the fans, combined with the action of the flow deflectors, generates a continuous and rapid homogenotion and circulation of the steam+air mixture which forms in the chamber, in the direction shown by the arrows in the functional diagram.

The internal impeller of the fan (the protection grid is removed): the vanes are made of a plastic material accepted by the F.D.A.; they reduce the weight of the impeller and ensure extremely high efficiency and perfect static and dynamic balancing.

The flow deflector ensures efficient and uniform circulation of the steam+air mixture during heating/sterilization and of the air during cooling.

The battery of stainless steel hollow plates for circulating the cooling water: these are definitely preferable to tube-nest exchangers, since they produce high turbulence in the circulating water and thus improving heat exchange. They are also easy to disassemble and inspect. The plates are hidden by the flow deflector.

At equal temperature and pressure conditions, air is in fact on the average 1.5 times denser than steam and would tend to stratify on the bottom of the chamber, producing unacceptable temperature gradients.

Once the heating and sterilization phases have ended, the cooling phase begins and develops as follows:
• the steam+air mixture present in the chamber is replaced with sterile compressed air at controlled pressure; this air continues to circulate by virtue of the action of the fans
• cold cooling water circulates in the batteries of cooling plates located in the two lateral circular sectors of the chamber.

However, the cooling rate is unavoidably much lower than in FOW autoclaves, since in this case it is based on two solid/gas heat exchanges, which notoriously have a low efficiency. Nonetheless, we try to improve their efficiency by keeping the air pressure in the chamber at a high value (within the limits set by the characteristics of the product) and by maintaining its circulation rate at a high level.

The chamber is cylindrical, usually single-wall, wich thick insulation and an aluminum-sheet outer casing. The construction material is class AISI 316 stainless steel.
Either one or two rectangular doors, inscribed in the circular cross-section.
These doors may be of two kinds:
• laterally sliding and fully automatic
• laterally hinged and semiautomatic; the doors engage and disengage their clamping devices with a transverse movement produced automatically by a geormotor, but the opening and closing action relative to the vertical hinges is manual.

In both cases, the gasket (made of solid silicone rubber) slides in a special slot formed by numeric-control milling in the frame of the chamber and it is activated by compressed air. The gasket and the slot have specially designed trapezoidal cross-sections to ensure perfect operation and tightness without requiring lubrication and vacuum for gasket retraction.

All valves and the entire hydraulic system are made of stainless steel.

AUTOMATIC LOADING/UNLOADING SYSTEMS

When it is necessary to sterilize large and heavy loads, it is sensible to resort to palletization systems featuring automatic handling.
The solution we have perfected for handling is extremely simple and efficient.
It consists of a loading bench located in front of the autoclave, where the train of pallets is prepared.
The bench has two rows of free rollers on which the pallets rest, and it is also provided with an underlying rod with a rack-like movement which pushes the pallets into the autoclave. The autoclave is also internally equipped with two rows of free rollers and therefore inside the chamber there are no sealed shafts, chains or gears: this means that all risks of leaks and all lubrication problems have been eliminated.
Usually, a second bench, arranged in front of the unloading door of the autoclave, removes the pallets by means of an extractor rack-roc

PROCESS CONTROL

As all the other sterilizers, also the counterpressure autoclaves are equipped with the Thema 3 process controller, specifically developed by our company for monitoring and controling sterilization processes. Please refer to the specific brochure for the desciption of this system.