How To Solve The Problem Of Wet Packs in Steam Autoclaves and Sterilizers.

As a manufacturer of steam autoclaves, we at Medi-Clave frequently hear feedback from current and prospective customers alike, regarding condensate issues (wet loads) in their chamber, post-sterilization, impeding satisfactory processing results. In fact, it could very well be the single leading technical issue we have run into over the past 15+ years of manufacturing sterilizers! To understand why, you really have to understand the myriad of potential causes, to appreciate the complexity of solving this simple problem.

When helping our clients identify the source of the issue, we begin by evaluation of the most common suspects first. Foremost among those suspects is the steam supply. Frequently we find that steam quality is the culprit in leading to excessive condensate formation within the autoclave. Our first recommendation to clients is to determine if you are placing excessive demand on the boiler. Next, examine the steam circuit/supply and look for potential areas of condensate formation such as dead legs or improperly trapped or insulated piping. The duty of a steam trap is to discharge condensate while not allowing the escape of live steam. The further away the steam line is from the heating source/medium, the more likely condensate is to form, and require removal from the system. One should consider proper insulation for piping,the further away the steam line is, the more the need for insulation. Lastly, have your sterilizer service people check the jacket steam trap and check valve at the drain port to be sure they are clear and functioning properly.

If you or your staff have no experience with proper steam supply design/piping, we would recommend that you contact Autoclave experts or Steam Sterilizer expertsfor an evaluation.

If the water content of the steam is 5% by mass, then the steam is said to be 95% dry and has a dryness fraction of 0.95.satisfactory dryness fraction is .97) Once you have established that the steam supply is not the source (of excess condensate), it is time to look more closely at what is being loaded into the vessel, the design of the sterilizer itself and perhaps the operation of the autoclave.

Another common cause of wet loads is the load itself. However tempting it may be to pack the chamber full of product, in order to keep up with demand, (dense packing) is frequently a cause of excessive condensation which cannot then be completely flashed off by subsequent steam injections. Large quantities of hard goods or even complex packaging can make proper steam circulation a challenge.  

Steam enters the chamber and contacts the product, it is essential that the steam collapse (condense) on the product in-order for the heat to be released to the load. But ultimately the water formation must be discharged through condensate management or re- vaporized in order to prevent contamination of the product. Removal of the excess water is crucial to prevention of insulating the load from the steam. That said, too much steam, at too fast a rate can result in excessive water formation which might overwhelm or swamp steam traps. Be sure that your steam traps are properly sized.

To dry the load after the fact, many users are tempted to employ excessively long deep vacuums at the end of the cycle. Because the chamber is heated (via the jacket) and the fact that water will flash off into steam at a lower temperature under vacuum, this is relatively successful. But what ultimately results is an unnecessarily long cycle time, and potentially a non-sterile load as water can collect in areas, and insulate the intended product from achieving temperature. Deep long post-sterilization vacuum drying phases are like closing the barn door after the horses have escaped.

When we are asked to assist under these conditions, we typically look to prevent (or greatly reduce) the formation of condensate by making sure that the load itself is brought up to a certain temperature prior to the introduction of steam. One simple way this can be accomplished is by defining a proper pre conditioning phase at the beginning of the cycle.

In Summary: Check the quality of your Facility Steam, including possible excessive demands on your boiler.
Check piping insulation from your steam source, to the autoclave. Check the way you pack your loads and do not over pack the chamber! Check the size and operation of the steam-traps and the drain globe valves leaking through. Check for clogged drains pipes and drain ports. Check your vacuum drying phase program settings and operation. Check or add a controlled pre-conditioning phase at the beginning of the cycle.

As an alternative you might wish to consider simply increasing the jacket temperature set-point, as long as it does not interfere with maintaining the temperature uniformity within the chamber during the sterilize dwell phase. A word of caution, merely increasing the jacket temperature could result in the super-heating of the steam, in the case that your condensate issue is not particularly bad, so use this strategy cautiously.

There are some unique approaches that can be causes, or solutions, to the condensate formation issue.

These include: Charge Rate Control (CRC). Many autoclaves are not equipped with a proportional control valve, or the necessary control system capability, to control the ramp up or charge rate of steam injection during the cycle. If a chamber does not have some means of valve configuration, or software limitations to control the rate that steam is added to the chamber, the result could be a flooding of the chamber with steam that results in instant condensate formation (this is a common problem found in South African Hospitals and can be effectively rectified  by adapting to the right approach) . If the steam injection were to be ramped up more slowly, the amount of steam and subsequent condensate can be more easily controlled.

There are many causes for condensate formation, in fact, condensing of steam is essential in heat transfer and hence sterilization, but too much condensate is detrimental. If you are experiencing such problems, try some of the above in identifying the cause, or contact Medi-Clave for assistance.

By: Johann Hoffman for Medi-Clave(Pty)Ltd South Africa