SVMS Steam Quality
Dryness Value

The purpose of the Steam Dryness Value Test is to ensure that an acceptable amount of moisture is present in the steam supply. If too little moisture were present, superheating of the steam may occur. Too little moisture may prevent sterilization conditions within the load, particularly because moisture is important in breaking down the cell structure of sporing organisms. If too much moisture is present, the load may not be able to be dried by completion of the cycle. Under the correct conditions wrapped loads are able to be stored for considerable periods in a sterile state. This is only true however where the wrapping material maintains its integrity by providing a microbiological barrier. If the load and its wrapping are damp when removed from the sterilizer this barrier is broken and can provide a path for re-contamination.

The method employed is the heat balance using a stainless steel vacuum flask.

The principal is that the flask is primed with a known mass of water at a known temperature. Steam is condensed in the flask thus raising the water temperature. The final mass and temperature of the water are then measured and placed into a calculation. If the final water temperature was lower or the final mass was greater, the steam would be 'wetter' (having a lower value).

Whilst the method is not regarded as a truly accurate measurement of moisture in the steam, it can be used to demonstrate acceptable dryness for sterilization purposes. A dryness value of 1.0 is equivalent to Dry Saturated Steam. For sterilization purposes, a factor of 0.9 is acceptable for nonmetal sterilizer loads. For loads containing metal, a factor of 0.95 is considered to be acceptable.

As the flask has to be connected within 0.5m of the sampling point, SVMS have incorporated a flask holder in the kit so that the flask can be mounted in a convenient position. This holder also serves as a measuring container to prime the flask.

For the engineers' convenience, the calculation can be performed manually or by the use of a computer spreadsheet. An electronic scientific calculator and CD containing all forms and calculations are supplied.


• Superheat
• Non-Condensable Gases
• Clean steam
• Back to SVMS Steam Quality Test Kits

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