Technical Data for Expansion Tanks

This dialog allows you to dimension diaphragm expansion tanks according to EN 12828.

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Name, Manufacturer, Order number

These fields are freely editable. This data is displayed in parts lists.

Calculation of Expansion Volume

To calculate the expansion volume V_e of the expansion tank at maximum operating temperature, enter the partial volume of system, the filling temperature and the maximum operating temperature of the system. Expansion is calculated using the medium table and is thus correctly adjusted when using a medium different from water.

The Partial volume of system is calculated by the pipe network calculation and consists of the fluid content of the calculated pipe network: the content of the drawn and possibly edited pipes, radiators, tanks, potable water heaters, general consumers and partial network ends. If more than one expansion tank exists in the system and the tank is to be dimensioned for only part of the system or if the actual system volume deviates from the calculated value you may edit this value. Activate the checkbox and enter the desired value. Deactivating the field resets it to the calculated value.

Water temperature at the time of filling is suggested to be 12 °C but can be edited.

Maximum operating temperature is taken from the supply water temperature of the system’s heat generator. Activate the checkbox in case this value needs to be changed. Deactivating the field resets it to the original value.

Safety Relief Valve

Relief pressure of the safety relief valve p_sv is suggested to be 2.5 bar. Enter the relief pressure of the safety relief valve used. From this value the dimensioning end pressure of the system p_e is calculated. If p_sv is smaller or equal to 3.0 bar, p_e is reduced by 0.5 bar. If p_sv is larger than 3.0 bar, p_e is reduced by 10 % bar.

Pre pressure calculation

The system height above vessel is taken from the model. The static pressure of the system is calculated using this value. Activate the checkbox to change this value. Deactivating the field resets it to the calculated value. Enter the cut-off temperature for the safety temperature limiter from the heat generator in the field Temperature limit (STL). A maximum value of 105 °C is suggested for the scope of DIN EN 12828. From these values, the pre pressure p₀ required when installing the expansion tank is calculated.

Expansion vessel volume

The values for Compensational water V_c and Expansion volume V_e are calculated and can not be edited. The compensational water comprises 0.5 % of the partial volume of the system, or at least 3 L.

The nominal volume V_n of the expansion tank is derived from that value. The calculated value relates to the minimum tank size, where start pressures ps min and ps max are equal. When filling the system, exactly this pressure has to be set.

The calculated nominal volume usually is not a commercially available size. Activate the checkbox Nominal volume and select the next greater commercially available size for the expansion tank. As a result, a difference between ps_a,min and ps_a,max emerges. The start pressure when filling the system should be set within those limits. As soon as the difference between ps_a,min and ps_a,max is equal or greater than 0.2 bar for the selected nominal volume, the note displayed will confirm that the nominal volume selected is sufficient.