To determine the pipe diameter in potable water networks of buildings numerous principles of calculation are necessary.

The revised version of DIN 1988 provides a simplified and differentiated method of calculation. The simplified method is suitable for clearly arranged pipes i.e. in residential buildings.

The differentiated method includes all pipes and local resistances and offers the highest accuracy as well as the most accurate approximation of real operating conditions.

The determining of the pipe diameter requires the following data:

• Minimum gauge pressure of supply or pressure in flow direction behind pressure reducing or boosting valve

• Head variations

• Loss of pressure due to apparatus i.e. water meter, filter

• Coefficients of loss for fittings and pipe connections

Part 3 of the DIN 1988 (Technical Rules for Potable Water Installations) stipulates the calculation principles for the determining of the pipe diameter.

The determining of the pipe diameter is based on the calculation of the loss of pressure in pipes.

Beside the diameter the loss of pressure depends on the length of the pipe, the pipe material an on the flow rate, dependent on the quantity and size of the water points to which the pipe is connected. 

The basis for determining the maximum flow rate should be calculated on the desired flow rate of each water point.

The simultaneous use resp. the peak pressure of flow of an installation part has to be determined by taking the calculation values from DIN 1988 T 3 as a basis. 

A further criterion for the selection of the pipe diameter is the maximum permissible flow rate.

Because of sonic reasons and for the limitation of water hammer, the calculated flow rate may not exceed the values of the table below.

Section of the installation

max. calculated flow

rate at run

</= 15 min. m/s </b>

> 15 min. m/s

Connecting pipes 

2

2

Service pipes:

Parts with poor drag reducing passage armatures (<2.5)

5

2

Parts with passage armatures

with a higher correction value loss

2,5

2