Waterhammer
ARTS can analyse waterhammer problems caused by sudden pump trip-out, with or without air vessel surge protection.

The first step is to draw the pump/rising main system on the design sheet and edit the relevant properties using the property pages.

Specialised features for waterhammer inlcude the ability to include the vertical profile of the rising main, so that ARTS can check gauge pressure fluctuation along the entire length of the rising main. The analysis procedure is iterative, based on the method of characteristics. The user can set several parameters relating to the accuracy and duration of the modeling, as well as the point at which the transient pressure fluctuation will be plotted.

A pump/rising main system and the set of output results generated for the system by execution of the Unsteady Flow command on the Analysis menu is illustrated above. The results are presented in 4 output windows, which present

• a textual summary of the system data, analysis settings and analytical results,
  

• a plot of the pump/system curve for steady flow conditions,
  

• a plot of the pressure fluctuation at the selected point on the rising main (the pump end node in this example) and
  

• plots of
  
  (a) the maximum and minimum pressure envelopes for the rising main,
  (b) the vapour pressure limit line,
  (c) the vertical profile of the rising main, and
  (d) the steady flow hydraulic grade line.
  

The pressure head parameter in the latter output window is plotted as potential head relative to the system datum, so that the gauge pressure at any point is represented by the vertical distance between the rising main and the pressure envelope curve at that point.

Where the pressure fluctuation caused by pump trip-out is excessive, its magnitude can be regulated by the use of an air vessel or, in the case of negative pressures, by the use of air valves. ARTS caters for pump/rising main systems, which include these devices. The air vessel is usually connected to the rising main at the upstream end by a short throttle pipe. The air vessel Main property page is shown here.