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Ensuring efficient steam temperature control

12 September 2021

Kieran Bennett explains how to select the right valve for steam temperature control. 

Temperature control using steam is utilised across various applications in the food and beverage sector. Combined with a temperature sensor and a controller, a control valve is key to a steam system, to regulate the flow.

Excessively large valves are often specified so ensuring that the right size control valve is chosen for a particular application can offer cost savings. The larger the valve, the higher its cost, and operating expenses can also increase, requiring greater resources for actuation. The challenge of using over-sized valves can apply to new projects as well as existing installations, where often it's incorrectly assumed that like-for-like replacement is the correct requirement.

On a recent project, one Burkert customer requested a replacement for a 40mm valve for steam control. On initial enquiry, it emerged that the required valve was to fit 40mm pipework. Unlike fluid control, the size requirement of a steam control valve will nearly always be a smaller diameter than its adjoining pipework. Further, advances in technology since the original valve was installed over 15 years ago, means that today in all likelihood a smaller valve could be used to achieve the flow and actuation requirements demanded for this application.

Further investigation of the application took into account the volume of product to be temperature controlled, the available pressure and the timeframe within which the product needed to be heated. Aspects such as the surface area of heat transfer were also considered.

Data returned from the calculations showed that a maximum valve size of 25 mm was required for the application. For new applications, or the higher the number of existing valves to be replaced at a production facility, the greater the cost saving that can be achieved by correctly specifying valve size.

Failure to correctly specify the size of valve for steam control can also impact accuracy and performance. For applications such as pasteurised milk production, accurate control is essential to ensure the right temperatures are met. 

If the configuration is too small, the valve has an inadequate flow reserve, recommended to be a minimum of 10%, and therefore cannot offer the required control reliability or flexibility. Ultimately, if the valve is too small, it might not be possible to provide the desired flow rate and achieve the required temperature change.

Alternatively, if the valve size is too large, the system can face challenges maintaining the set temperature. With an over-sized valve, during heating it is nearly fully open, but to stop increasing the temperature and maintain the level, it has to be nearly fully closed. This way, an over-sized valve is too large to achieve the required precision, and temperature fluctuations result with an oscillating effect as the valve repeatedly attempts to compensate.

Choosing a valve 
Where precision control of steam is required, a globe valve will provide the greatest accuracy. While allowing a moderate flow of 13m3/hr, a globe valve ensures control accuracy to +/- 0.5 - 1.0°C. In combination, Bürkert's piston actuators can provide positional accuracy to within 0.1%, ensuring optimum control for steam and wider application types.

For some applications, this level of accuracy is not required. For example, in one dairy, steam is used in cheese production. The condensate from the boiling process is used to heat a secondary water supply for a staff washroom. The required temperature is approximately 60°C, but a difference of several degrees either way is not significant.

In a case like this, to save costs, a ball or butterfly valve can be specified. Offering accuracy of +/- 5°C, which may be sufficient for more general temperature control purposes, a ball or butterfly valve provides full flow of 48m3/hr.

For hygienic applications however, where there is a requirement for the media to be separated, a diaphragm valve should always be used. 

Regardless of the valve, actuator or positioner used, to optimise efficiency and performance in steam temperature control, the application has to be specified correctly at the outset. 

Kieran Bennett is field segment manager, Hygienic-Food & Beverage at Bürkert.


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