Calculation Method Tab

Owned by Steve Peregrine
Last updated: Jun 20, 2020
3 min read

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Calculation Method Tab

In the ‘Calculation Method’ tab, we have the option to change the way that the data is presented from the ‘WinCan’ method (is the default method) to the SV-P91 method (formerly known as VAV-P50):

SV-P91 modelling display.

The SV-P91 system is a Swedish building (SV = Svensk Vaten or Swedish Water) standard specification for newly built sewers which describes acceptable limits for the ‘straightness’ of a pipe when its inclination is measured. There is no other standard like this in the world and it used by many countries in the absence of any alternative.

As mentioned, the specification is for newly built sewers, so it may not be considered appropriate to use it on old pipes that are maybe 100 years old, but the tolerance values can be adjusted by the engineer if they wish to use the same logic but soften (or harden) the bands for a ‘good’ pipe.

When this option is activated, there are 3 sets of tramlines activated on the graph, in pairs either side of the lower brown line (the ‘perfect’ invert line of the sewer). These are tolerance bands for good (Class A), medium (Class B) and bad (Class C) and are defined in millimetres. The values for these classes are defined in SV-P91 and are dependent on the measured inclination of the pipe from the GPS data and the pipe diameter, so good GPS data is essential for this type of output.

Checking the boxes in the ‘Out A', ‘Out B’ and ‘Out C’ boxes activates the thick coloured parts of the thick blue line where the curve crosses the tolerance line so that the engineer can see very quickly if the pipe inclination test is confirming that the installation is a Class A, B or C. These classes are very tight as defined in the standard.

By default, the classes are set to the SV-P91 values, but by clicking on the ‘Class’ button, we can modify the values to suit our own needs or maybe contractual definitions for other countries.

Different Values in these Pages

You may be asking why the inclination and delta height values shown in the image at the top of this page do not match with the manually calculated values in the section ?

In the other section we calculated:

  • Fall = -0.223 m

  • Gradient = -0.97 %

But in the WinCan inclination panel we are seeing:

  • Fall = -0.22 m

  • Gradient = -1.03 %

The reason for these differences are:

  • The difference between -0.223 and -0.22 is simply a decimal place rounding to 2 rather than 3 decimal places.

  • The difference in the gradient is because the other page takes the actual measured values for the entire 23 m of the pipe but the inclination test only considers 21.75 m as has been discussed previously. So, if we use the measurement test difference of 21.75 m then we get (−0.223 × 100) ÷ 21.75 = −1.03 % which is what is displayed on the VX panel.