Autoclave water quality and limescale protection

Autoclave water quality and limescale protection

Hard water, if untreated, will quickly reduce the efficiency and appearance of your autoclave. Thankfully we have a simple and cost effective solution available to fix it.

Much of the United Kingdom is serviced by water that is classified as ‘hard’. Hard water contains dissolved magnesium and calcium ions. When heated, limescale (a solid containing calcium carbonate) is produced. If left untreated limescale sticks the outside of heating elements, autoclave chamber walls, water level sensors, reduces pipe size and even blocks pipes which can cause serious damage and reduced efficiency. Heaters coated with scale require more energy to heat the water, which increases running costs and can lead to premature failures. Hard water will also leave residue on the product(s) being sterilized, especially glassware and media. 


To illustrate, some examples of autoclave internals affected by untreated hard water are shown below.

Picture 1: The inside of a sterilization chamber where limescale has formed on the heating elements, causing the heaters to eventually fail. Similarly, the water cooling coils were virtually useless.

Picture 2: The base tray and water level sensor in the chamber of the same machine.

Pictures 1 and 2 were of an autoclave less than a year old. The build-up of scale caused an unexpected failure and cost to the customer. We always recommend a water softener and/or minimum water quality requirements to prevent or eliminate scale accumulation.

Picture 3: The inside of a steam generator. Here the scale had to be chipped off manually during an insurance inspection. Again the unit was not much more than one year old.


The damaging effect that hard water can have means it is always beneficial to ‘soften’ the water before it enters the autoclave or steam generator. Astell recommends fitment of a Water Softener system to reduce the build-up of limescale on heaters, valves and pipework in laboratories affected by hard water. It is especially important for units supplied with integral steam generators to include some form of water treatment in order to safeguard the long-term performance.

As an example, Astell can supply a Water Softener that includes a separate brine tank, allowing installation in difficult or restricted positions. The unit works automatically to soften the water before it enters the sterilizer. The only ongoing requirement is to periodically top it up with salt.
Full details, including service requirements are available upon request. Quote option ref. AAW002.

Most sterilizers with in-chamber heating rely on H2O having conductivity to sense the presence of water. Astell can produce sterilizers and steam generators with float switches to sense the water level, so you can use clean water to produce steam which will not leave any limescale or residue.

Note: Autoclave failures caused by hard water may not be covered by Astell’s equipment warranty. It is the user’s responsibility to inform and take precaution against hard water damage. To check if you are in a hard water area it is usually best to visit the website of your local provider. For help identifying this in the UK click here.

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