Hello good morning;

I am modeling a surge tank to protect a pipe for transient event.

When I dont consider headloss coefficient ( Headloss coefficient = 0) tthe system works normally but when I consider a headloss coefficient different to 0 (always positive), HAMMMER dont compute. 

Additional Surge Tank input data:

• Operating Range type: elevation
• Elevation (Base): 726.91
• Elevation (Minimum): 726.91
• Elevation initial:731
• Elevation (Maximum):734

• Elevation (physical): 726.46
• Volume(inactive): 0
• Section: Circular
• Diameter (m): 0.10 (it is a 4" stand pipe)
• Treat as Juction: True

• Surge Tank Type: Simple
• Has check valve: False
• Weir coefficient:1.84
• Weir Length: 0.5 m
• Diamter orifice (mm): 100
• Ratios of losses:2.5
• Headloss coefficient: ?

• The pipe is a 450 mm diameter ductil Iron (lenght 6100m) with a flow of 100 l/s 
• Reservoir elevation: 731.23m
• Valve close time:120 seg.

Where do you think is the error? Maybe the little diameter of the onlet and surge tank (4"=0.1m = 100mm) 

Thank you very much for your support

Kind regards.